101 Amazing Earth Facts
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1. What is the hottest place on Earth?
Count one wrong if you guessed Death Valley in California. True enough on many days. But El Azizia in Libya recorded a temperature of 136 degrees Fahrenheit (57.8 Celsius) on Sept. 13, 1922 -- the hottest ever measured. In Death Valley, it got up to 134 Fahrenheit on July 10, 1913.
2. And the coldest place around here?
Far and away, the coldest temperature ever measured on Earth was -129 Fahrenheit (-89 Celsius) at Vostok, Antarctica, on July 21, 1983.
3. What makes thunder?
If you thought, "Lightning!" then hats off to you. But I had a more illuminating answer in mind. The air around a lightning bolt is superheated to about five times the temperature of the Sun. This sudden heating causes the air to expand faster than the speed of sound, which compresses the air and forms a shock wave; we hear it as thunder.
4. Can rocks float?
In a volcanic eruption, the violent separation of gas from lava produces a "frothy" rock called pumice, loaded with gas bubbles. Some of it can float, geologists say. I've never seen this happen, and I'm thankful for that.
5. Can rocks grow?
Yes, but observing the process is less interesting than watching paint dry. Rocks called iron-manganese crusts grow on mountains under the sea. The crusts precipitate material slowly from seawater, growing about 1 millimeter every million years. Your fingernails grow about the same amount every two weeks.
6. How much space dust falls to Earth each year?
Estimates vary, but the USGS says at least 1,000 million grams, or roughly 1,000 tons of material enters the atmosphere every year and makes its way to Earths surface. One group of scientists claims microbes rain down from space, too, and that extraterrestrial organisms are responsible for flu epidemics. There's been no proof of this, and I'm not holding my breath.
7. How far does regular dust blow in the wind?
A 1999 study showed that African dust finds its way to Florida and can help push parts of the state over the prescribed air quality limit for particulate matter set by the U.S. Environmental Protection Agency. The dust is kicked up by high winds in North Africa and carried as high as 20,000 feet (6,100 meters), where it's caught up in the trade winds and carried across the sea. Dust from China makes its way to North America, too.
8. Where is the worlds highest waterfall?
The water of Angel Falls in Venezuela drops 3,212 feet (979 meters).
9. What two great American cities are destined to merge?
The San Andreas fault, which runs north-south, is slipping at a rate of about 2 inches (5 centimeters) per year, causing Los Angeles to move towards San Francisco. Scientists forecast LA will be a suburb of the City by the Bay in about 15 million years.
10. Is Earth a sphere?
Because the planet rotates and is more flexible than you might imagine, it bulges at the midsection, creating a sort of pumpkin shape. The bulge was lessening for centuries but now, suddenly, it is growing, a recent study showed. Accelerated melting of Earth's glaciers is taking the blame for the gain in equatorial girth. -
11. What would a 100-pound person weigh on Mars?
The gravity on Mars is 38 percent of that found on Earth at sea level. So a 100-pound person on Earth would weigh 38 pounds on Mars. Based on NASA's present plans, it'll be decades before this assumption can be observationally proved, however.
12. How long is a Martian year?
It's a year long, if you're from Mars. To an earthling, it's nearly twice as long. The red planet takes 687 Earth-days to go around the Sun -- compared to 365 days for Earth. Taking into account Mars' different rotational time (see #13 below) calendars on Mars would be about 670 days long with some leap days needed to keep things square. If you find one, please mail it to me. I'm curious how they worked out the months, given they have two moons. [The initial publication of this fact mistakenly said a Mars calendar would have 687 days.]
13. How long is the average Martian day?
A Martian can sleep (or work) and extra half-hour every day compared to you. Mars days are 24 hours and 37 minutes long, compared to 23 hours, 56 minutes on Earth. A day on any planet in our solar system is determined by how long it takes the world to spin once on its axis, making the Sun appear to rise in the morning and sending it down in the evening.
14. What is the largest volcano?
The Mauna Loa volcano in Hawaii holds the title here on Earth. It rises more than 50,000 feet (9.5 miles or 15.2 kilometers) above its base, which sits under the surface of the sea. But that's all volcanic chump change. Olympus Mons on Mars rises 16 miles (26 kilometers) into the Martian sky. Its base would almost cover the entire state of Arizona.
15. What was the deadliest known earthquake?
The worldÂ’s deadliest recorded earthquake occurred in 1557 in central China. It struck a region where most people lived in caves carved from soft rock. The dwellings collapsed, killing an estimated 830,000 people. In 1976 another deadly temblor struck Tangshan, China. More than 250,000 people were killed.
16. What was the strongest earthquake in recent times?
A 1960 Chilean earthquake, which occurred off the coast, had a magnitude of 9.6 and broke a fault more than 1,000 miles (1,600 kilometers) long. An earthquake like that under a major city would challenge the best construction techniques.
17. Which earthquake was more catastrophic: Kobe, Japan or Northridge, California?
The 1994 Northridge earthquake had a magnitude of 6.7 was responsible for approximately 60 deaths, 9,000 injuries, and more than $40 billion in damage. The Kobe earthquake of 1995 was magnitude 6.8 and killed 5,530 people. There were some 37,000 injuries and more than $100 billion in economic loss.
18. How far is it to the center of the Earth?
The distance from the surface of Earth to the center is about 3,963 miles (6,378 kilometers). Much of Earth is fluid. The mostly solid skin of the planet is only 41 miles (66 kilometers) thick -- thinner than the skin of an apple, relatively speaking.
19. What is the highest mountain?
Climbers who brave Mt. Everest in the Nepal-Tibet section of the Himalayas reach 29,035 feet (nearly 9 kilometers) above sea level. Its height was revised upward by 7 feet based on measurements made in 1999 using the satellite-based Global Positioning System.
20. Has the Moon always been so close?
It used to be much closer! A billion years ago, the Moon was in a tighter orbit, taking just 20 days to go around us and make a month. A day on Earth back then was only 18 hours long. The Moon is still moving away -- about 1.6 inches (4 centimeters) a year. Meanwhile, Earth's rotation is slowing down, lengthening our days. In the distant future, a day will be 960 hours long! -
20. Has the Moon always been so close?
Question: Why?
It used to be much closer! A billion years ago, the Moon was in a tighter orbit, taking just 20 days to go around us and make a month. A day on Earth back then was only 18 hours long. The Moon is still moving away -- about 1.6 inches (4 centimeters) a year. Meanwhile, Earth's rotation is slowing down, lengthening our days. In the distant future, a day will be 960 hours long!
Answer: A billion years ago, the Moon was much closer to Earth than it will be tonight. Its tighter orbit meant it needed just 20 days to go around us, to make a lunar month. Other things were noticeably different, too. A day on Earth back then was only 18 hours long. People were probably wishing, "If only I had 24 hours in a day"
Okay, there were no people then, but the critters of the time eventually got their wish. In the intervening eons, the Moon has been drifting away. Each year, it moves about 1.6 inches (4 centimeters) farther into space.
It is a coincidence of orbital and species evolution that we humans are on this planet during an era when we can work 24/7, should that be demanded.
Also by coincidence, we're here when the Moon's apparent size in the sky is equal to that of the Sun, so that a total solar eclipse is possible. Furthermore, we arrived comfortably after the pockmarked satellite began showing just one face to Earth, providing that immutable and unchanging beacon we call a full Moon, cosmic governor of terrestrial love and a lot of loony ideas.
Or, one could argue, none of this is coincidence at all. If not for the Moon, some say, love as we know it would never have happened and we wouldn't be here to contemplate Earth's orbiting treasure.
The Moon has had dramatic effects on our planet and the life that inhabits it, researchers believe. The Moon stabilizes Earth's rotation, for example, preventing otherwise dramatic movements of the poles that would fuel climate swings that some scientists figure might have doomed any chance for life to form, let alone evolve.
And biologists speculate that tides, generated mostly by the Moon, would have been a logical place for life to originate. Sea creatures might have then used tidal regions as experimental sites for testing the habitability of land, and therefore as an excuse to develop lungs. Put short, your gilled ancestors might have used the Moon like a gravitational guiding light to the first non-aquatic procreation.
In that sense, the only coincidence in all this is the fact that the Moon ever came to exist in the first place. For there was a brief time in the early history of our planet, likely 100 million years or less, when there was no Moon in the sky.
4.5 billion years ago
The Earth has recently been forged out of the detritus of star formation, assembled from dust that became rock, then boulders that collided and grew. Other planetary hopefuls roam the solar system. Impacts are frequent. The scene is hectic.
A large rock, about the size of Mars, is doomed. It's heading toward Earth, destined for a slightly off-center impact that will set everything that isn't already rotating into a frenzy of spin.
Upon impact, material from the incoming object and from the new Earth is cast into space. A ring of debris orbits the planet, and in an amazingly short amount of time -- about one day -- it begins to coalesce into a satellite. It takes somewhere between 1 and 100 years for the Moon to gather most of the stuff into a ball.
There are other theories for how the Moon was born, but this one is widely accepted as the most plausible.
Earth may or may not have been rotating before the impact, but it certainly was afterward. Importantly, the orbital and rotational mechanics of this new Earth-Moon system were then planned out for all time. The impact imparted angular moment on the system, a spin that could never be destroyed, the laws of physics tell us. Curiously, the specific relationships would change over time -- dramatically -- and the shifts continue today.
The face of change
During the past 4.5 billion years, Earth's overwhelming gravity has slowed the Moon's rotation down and pushed the satellite away. The cause is complex, involving tides, which we'll discuss below. One amazing result, for now, is a readily observable set of very interesting facts: It takes the Moon 29.5 days to make one revolution about its axis. All the while, of course, the Moon is also going around the Earth. This orbit also takes 29.5 days.
Because the Moon's orbit and rotation times are the same, the satellite always shows the same face to Earth. We see that face because sunlight reflects off it (the Moon does not make its own light).
On the Moon, all this means that the Sun rises every four weeks, roughly. It also means there is no "dark side" of the Moon, at least not to someone living in any hypothetical Lunaville. The side of the Moon we cannot see from Earth gets its full share of sunshine periodically, when the Moon is between Earth and the Sun. In this configuration, the Moon is said to be new, and it reflects no sunlight our way.
There was a time, however, when the timing was much different.
Shifting tides
Gravity is said to be the weakest of all the fundamental forces. But one aspect of it is very consequential: Gravity never goes away. It weakens with distance, but it is always at work. This fact is the primary driver of tides. The side of Earth nearest the Moon always gets tugged more than the other side, by about 6 percent.
Hey, you might say, there are two high tides on this planet at any given moment. True. And another far more complex set of phenomena explains this.
The Moon does not just go around the Earth. In reality, the two objects orbit about a common gravitational midpoint, called a barycenter. The mass of each object and the distance between them dictates that this barycenter is inside Earth, about three-fourths of the way out from the center.
So picture this: The center of the Earth actually orbits around this barycenter, once a month. The effect of this is very important. Think, for a second, of a spacecraft orbiting Earth. Its astronauts experience zero gravity. That's not because there's no gravity up there. It's because the ship and its occupants are constantly falling toward Earth while also moving sideways around the planet. This sets up a perpetual freefall, or zero-g.
Like the orbiting spaceship, the center of the Earth is in free-fall around the barycenter of the Earth-Moon system.
Here's the kicker: On the side of Earth opposite the Moon, the force of the Moon's gravity is less than at the center of the Earth, because of the greater distance. It can actually be thought of as a negative force, in essence, pulling water away from the Moon and away from Earth's surface -- a second high tide.
Our planet rotates under these constantly shifting tides, which is why high and low tides are always moving about, rolling in and rolling out as far as observers on the shore are concerned.
The Sun, too, has a tidal effect on Earth, but because of its great distance it is responsible for only about one-third of the range in tides. When the Earth, Moon and Sun are aligned (at full or new Moon), tides can be unusually dramatic, on both the high and low ends. When the Moon is at a 90-degree angle to the Sun in our sky (at first quarter or last quarter) tides tend to be mellower.
Effect on orbits
Earlier, we said tides are at the root of alterations in the entire Earth-Moon orbital system. Here's how: Earth spins once a day, while the Moon goes around the planet at a more plodding pace, once a month. So the planet is always trying to drag tides along, and it succeeds a bit.
The high-tide bulges are pulled just ahead of an imaginary line connecting the centers of Earth and the Moon. It might seem rather amazing, but a terrestrial bulge of water has enough mass to tug at the Moon from yet another angle. The effect is to constantly prod the Moon into a higher orbit, which explains why it is moving away from us.
The Moon, meanwhile, is yanking back on the tidal bulges. So the water, down where it meets the ocean floor, rubs against Earth. This slows the planet down, explaining why there are 24 hours in a day instead of the mere 18 of a billion years ago.
Finally, we need to bring up another factor that helped all these opposing dynamics reach an agreement of sorts:
More than just water is pulled up by tides. Earth's solid self actually stretches, too. And Earth's gravity lifts tides on the Moon, raising relatively small bulges in the seemingly solid satellite. (Similarly, Jupiter's gravity raises tides on its icy moons in the frigid outer region of the solar system, stretching some so dramatically that the action generates enough heat to maintain liquid oceans under their frozen shells, scientists believe.)
Back to our Moon: Continual tugging on the lunar bulges reduced the Moon's rotation rate over time. When the rotation had slowed to the point that it equaled the time it took for the Moon to go around the Earth, the lunar bulges lined up with our planet, and the slowdown stopped. At that moment, one face of the Moon became forever locked in our direction.
A moment in time
Things continue to change, of course.
Earth's rotation rate is still slowing down -- our days are getting longer and longer. Eventually, our planet's tidal bulges will be assemble along that imaginary line running through the centers of both Earth and the Moon, and our planetary rotational change will pretty much cease. Earth's day will be a month long. When this happens, billions of years from now, the terrestrial month will be longer -- about 40 of our current days -- because during all this time the Moon will continue moving away.
In this future picture, any lunar colonists would then henceforth see just one face of Earth. You can imagine this setup by stretching your arm out and looking at your palm. Now twirl around. You're face and your palm stare at each other the whole time. If the United States happens to be on the back of your head, well, just think what people there do not see. -
21. Where is the lowest dry point on Earth?
The shore of the Dead Sea in the Middle East is about 1,300 feet (400 meters) below sea level. Not even a close second is Bad Water in Death Valley, California, at a mere 282 feet below sea level.
22. Good thing California isn't sinking further, right?
Actually parts of it are, which is so interesting that I snuck this non-question onto the list. In a problem repeated elsewhere in the country, the pumping of natural underground water reservoirs in California is causing the ground to sink up to 4 inches (11 centimeters) per year in places. Water and sewage systems may soon be threatened.
23. What is the longest river?
The Nile River in Africa is 4,160 miles (6,695 kilometers) long.
24. What is the most earthquake-prone state in the United States?
Alaska experiences a magnitude 7 earthquake almost every year, and a magnitude 8 or greater earthquake on average every 14 years. Florida and North Dakota get the fewest earthquakes in the states, even fewer than New York.
25. What's the driest place on Earth?
A place called Arica, in Chile, gets just 0.03 inches (0.76 millimeters) of rain per year. At that rate, it would take a century to fill a coffee cup.
26. What causes a landslide?
Intense rainfall over a short period of time can trigger shallow, fast-moving mud and debris flows. Slow, steady rainfall over a long period of time may trigger deeper, slow-moving landslides. Different materials behave differently, too. Every year as much as $2 billion in landslide damage occurs in the United States. In a record-breaking storm in the San Francisco area in January 1982, some 18,000 debris flows were triggered during a single night! Property damage was over $66 million, and 25 people died.
27. How fast can mud flow?
Debris flows are like mud avalanches that can move at speeds in excess of 100 mph (160 kph).
28. Do things inside Earth flow?
You bet. In fact, scientists found in 1999 that molten material in and around Earth's core moves in vortices, swirling pockets whose dynamics are similar to tornadoes and hurricanes. And as you'll learn later in this list, the planet's core moves in other strange ways, too.
29. What is the wettest place on Earth?
Lloro, Colombia averages 523.6 inches of rainfall a year, or more than 40 feet (13 meters). That's about 10 times more than fairly wet major cities in Europe or the United States.
30. Does Earth go through phases, like the Moon?
From Mars, Earth would be seen to go through distinct phases (just as we see Venus change phases). Earth is inside the orbit of Mars, and as the two planets travel around the Sun, sunlight would strike our home planet from different angles during the year. Earth phases can be seen in recent photographs taken by Mars Global Surveyor and the European Mars Express. -
31. What is the largest canyon?
The Grand Canyon is billed as the world's largest canyon system. Its main branch is 277 miles (446 kilometers) long. But let's compare. Valles Marineris on Mars extends for about 3,000 miles (4,800 kilometers). If added it to a U.S. map, it would stretch from New York City to Los Angeles. In places this vast scar on the Martian surface is 5 miles (8 kilometers) deep.
32. What is the deepest canyon in the United States?
Over the eons, the Snake River dug HellÂ’s Canyon along the Oregon-Idaho border. It is more than 8,000 feet (2.4 kilometers) deep. In contrast, the Grand Canyon is less than 6,000 feet deep -- a bit more than a mile.
33. Is Earth the largest rocky planet in the solar system?
Just barely! Earth's diameter at the equator is 7,926 miles (12,756 kilometers). Venus is 7,521 miles (12,104 kilometers) wide. Mercury and Mars, the other two inner rocky planets, are much smaller. Pluto is rocky, too, but it's comparatively tiny (and some say it is not a planet at all).
34. How many of EarthÂ’s volcanoes are known to have erupted in historic time?
About 540 volcanoes on land are known. No one knows how many undersea volcanoes have erupted through history.
35. Is air mostly oxygen?
Earth's atmosphere is actually about 80 percent nitrogen. Most of the rest is oxygen, with tiny amounts of other stuff thrown in.
36. What is the highest waterfall in the United States?
Yosemite Falls in California is 2,425 feet (739 meters).
37. What percentage of the worldÂ’s water is in the oceans?
About 97 percent. Oceans make up about two-thirds of Earth's surface, which means that when the next asteroid hits the planet, odds are good it will splash down.
38. Which two landmasses contain the vast majority of the EarthÂ’s fresh water supply?
Nearly 70 percent of the Earth's fresh-water supply is locked up in the icecaps of Antarctica and Greenland. The remaining fresh-water supply exists in the atmosphere, streams, lakes, or groundwater and accounts for a mere 1 percent of the Earth's total.
39. Which of the EarthÂ’s oceans is the largest?
The Pacific Ocean covers 64 million square miles (165 million square kilometers). It is more than two times the size of the Atlantic. It has an average depth of 2.4 miles (3.9 kilometers).
40. Why is Earth mostly crater-free compared to the pockmarked Moon?
Earth is more active, in terms of both geology and weather. Much of our planet's geologic history was long ago folded back inside. Some of that is regurgitated by volcanoes, but the results are pretty hard to study. Even more recent events evident on the surface -- craters that can by millions of years old -- get overgrown by vegetation, weathered by wind and rain, and modified by earthquakes and landslides. The Moon, meanwhile, is geologically quiet and has almost no weather; its craters tell a billions-year-long tale of catastrophic collisions. Interestingly, some of the oldest Earth rocks might be awaiting discovery on the Moon, having been blasted there billions of years ago by the very asteroid impacts that rattle both worlds. -
41. How much surface area does Earth contain?
There are 196,950,711 square miles (510,100,000 square kilometers).
42. What is the largest lake in the world?
By size and volume it is the Caspian Sea, located between southeast Europe and west Asia.
43. Where do most earthquakes and volcanic eruptions occur on Earth?
The majority occur along boundaries of the dozen or so major plates that more or less float on the surface of Earth. One of the most active plate boundaries where earthquakes and eruptions are frequent, for example, is around the massive Pacific Plate commonly referred to as the Pacific Ring of Fire. It fuels shaking and baking from Japan to Alaska to South America.
44. How hot are the planet's innards?
The temperature of Earth increases about 36 degrees Fahrenheit (20 degrees Celsius) for every kilometer (about 0.62 miles) you go down. Near the center, its thought to be at least 7,000 degrees Fahrenheit (3,870 Celsius).
45. What three countries have the greatest number of historically active volcanoes?
The top three countries are Indonesia, Japan, and the United States in descending order of activity.
46. How many people worldwide are at risk from volcanoes?
As of the year 2000, USGS scientists estimated that volcanoes posed a tangible risk to at least 500 million people. This is comparable to the entire population of the world at the beginning of the seventeenth century!
47. Which of the following sources stores the greatest volume of fresh water worldwide: lakes, streams or ground water?
Groundwater comprises a 30 times greater volume than all freshwater lakes, and more than 3,000 times what's in the worldÂ’s streams and rivers at any given time. Groundwater is housed in natural underground aquifers, in which the water typically runs around and through the stone and other material.
48. Which earthquake was larger, the 1906 San Francisco earthquake or the 1964 Anchorage, Alaska, temblor?
The Anchorage earthquake had a magnitude of 9.2, whereas the San Francisco earthquake was a magnitude 7.8. This difference in magnitude equates to 125 times more energy being released in the 1964 quake and accounts for why the Anchorage earthquake was felt over an area of almost 500,000 square miles (1,295,000 square kilometers).
49. Which earthquake was more destructive in terms of loss of life and relative damage costs, the 1906 San Francisco earthquake or the 1964 Anchorage earthquake?
The 1906 San Francisco earthquake tops this category. It was responsible for 700 deaths versus 114 from the Anchorage earthquake. Property damage in San Francisco was also greater in relative terms due to the destructive fires that destroyed mostly wooden structures of the time.
50. Is Earth's core solid?
The inner portion of the core is thought to be solid. But the outer portion of the core appears molten. We've never been there though, so scientists aren't sure of the exact composition. A radical Hollywood-like idea was recently put forth to blow a crack in the planet and send a probe down there to learn more. An interesting bit of recent evidence shows Mars' core may be similarly squishy. Scientists figured this out by studying tides on Mars. -
Scientists figured this out by studying tides on Mars.
A new study concludes that the core of Mars is the consistency of the syrupy goop found inside chocolate-covered fruit candy.
The inference was made simply by noting minor changes in the position of a Mars-orbiting spacecraft, caused by tides.
Yes, tides on Mars. While one commonly thinks of tides having to do with oceans on Earth, and being generated only by the Moon, the inner parts of heavenly bodies endure tides, too. On Earth, gravity from both the Moon and the Sun fuel ocean tides and simultaneously stretch and pull the entire planet by less noticeable amounts.
Mars, too, is tidally tweaked by the Sun.
Scientists have not until now had any firm evidence whether the core of Mars was solid or liquid, though they had suspected it would be at least partly liquid, and they knew it was mostly iron. The new study finds that at least the outer portion of the core is indeed molten, making it similar to the cores of Earth and Venus. The conclusion is based on three years worth of data showing changes in the orbital characteristics of the Mars Global Surveyor.
The study was led by Charles Yoder at NASA's Jet Propulsion Laboratory and was published today in the online version of the journal Science.
Yoder and his colleagues tracked a radio signal emitted by the spacecraft to monitor the craft as its orbital plane tilted gradually. This shift is caused by the planet's tidal bulge -- the extent to which the Sun physically distorts the planet. A continually moving "tidal bulge" on Mars exerts an ever-changing gravitational influence on the spacecraft.
The spacecraft's movements, in turn, revealed the extent of the bulge.
Knowlege of the amplitude of the tidal bulge was compared with models of Mars' tidal deformation assuming a liquid or a solid core, explained Alex Konopliv, a JPL scientist who did data analysis for the study. A smaller bulge would indicate a solid core whereas a larger bulge would suggest a more flexible planet and, thus, a liquid core.
"The amplitude is consistent with a fluid core, not a solid core," at least in the outer portion, Konopliv said.
Additional information for the study came from previous measurements of the precession of Mars' rotation. Like Earth, the Red Planet's axis of rotation is not steady, but instead proscribes an imaginary cone-shaped feature in space as it shifts over time.
It takes 170,000 years for the Martian axis to make one revolution, Konopliv said, effectively drawing a circle on some imaginary plane above the pole. "The precession rate indicates how much the mass of Mars is concentrated toward the center. A faster precession rate indicates a larger dense core compared."
In addition to iron, the new study indicates there is also some lighter element in the core, possibly sulfur, Yoder told SPACE.com. The study also pinned the core's radius down to between 945 and 1,143 miles (1,520 and 1,840 kilometers).
The average radius of Mars is 2,106 miles (3,390 kilometers), just more than half that of Earth. But Mars is less dense -- containing only 11 percent as much mass as Earth.
More study is needed, the researchers said, to understand how the apparently liquid core might have affected evolution, size and composition of the core as well as higher layers of the planet's innards. -
51. Does all of Earth spin at the same rate?
The solid inner core -- a mass of iron comparable to the size of the Moon -- spins faster than the outer portion of the iron core, which is liquid. A study in 1996 showed that over the previous century, the extra speed caused the inner core to gain a quarter-turn on the planet as a whole. So the inner core makes a complete revolution with respect to the rest of Earth in about 400 years. Immense pressure keeps it solid.
52. How many people have been killed by volcanoes during the last 500 years?
At least 300,000. Between 1980 and 1990, volcanic activity killed at least 26,000 people.
53. How much of the EarthÂ’s surface consists of volcanic rock?
Scientists estimate that more than three-quarters of EarthÂ’s surface is of volcanic origin-- that is, rocks either erupted by volcanoes or molten rock that cooled below ground and has subsequently been exposed at the surface. Most of EarthÂ’s volcanic rocks are found on the sea floor.
54. Can an earthquake cause a tsunami?
If the earthquake originates under the ocean, yes. Near the earthquakeÂ’s epicenter, the sea floor rises and falls, pushing all the water above it up and down. This motion produces a wave that travels outward in all directions. A tsunami can be massive but remain relatively low in height in deep water. Upon nearing the shore, it is forced up and can reach the height of tall buildings. One in 1964 was triggered in Alaska and swamped the small northern California town of Crescent City, moving train cars several blocks and killing several people there. Asteroids can cause tsunami, too.
55. Are all tsunamis high waves when they strike a coastline?
No, contrary to many artistic images of tsunamis, most do not result in giant breaking waves. Rather, most tsunamis come onshore more like very strong and fast tides. The water can rise higher than anyone along a given shore area has ever seen, however. [Model of an East Coast tsunami]
56. How much of the EarthÂ’s land surface is desert?
About one-third.
57. What's the deepest place in the ocean?
The greatest known depth is 36,198 feet (6.9 miles or 11 kilometers) at the Mariana Trench, in the Pacific Ocean well south of Japan near the Mariana Islands.
58. What is the fastest surface wind ever recorded?
The fastest "regular" wind that's widely agreed upon was 231 mph (372 kph), recorded at Mount Washington, New Hampshire, on April 12, 1934. But during a May 1999 tornado in Oklahoma, researchers clocked the wind at 318 mph (513 kph). For comparison, Neptune's winds can rage to 900 mph (1,448 kph).
59. How much fresh water is stored in the Earth?
More than two million cubic miles of fresh water is stored in the planet, nearly half of it within a half-mile of the surface. Mars, too, appears to have a lot of water near its surface, but what's been detected so far is locked up as ice; nobody has estimated how much might be there.
60. How old is Earth?
Our planet is more than 4.5 billion years old, just a shade younger than the Sun. Recent evidence actually shows that Earth was formed much earlier than previously believed, just 10 million years after the birth of the Sun, a stellar event typically put at 4.6 billion years ago. -
Asteroids can cause tsunami, too.
Question: Why?
Answer: Big asteroids can be extra deadly when they strike the ocean, carving aquaticcraters and sending huge waves in all directions. These tsunami can wreakdestruction on shores thousands of miles away. Bad news for people livingin coastal areas, but it could be a lucky break for the rest of mankind:The same impact on land would throw dust high into the atmosphere and couldblock sunlight for many months, possibly causing global starvation andmass extinctions.
Dangerous waves
The surface of water is verygood at transferring energy, in the form of waves, across great distances.In 1960, for example, an earthquake near Chile created a series of wavesthat crossed the Pacific Ocean and killed several hundred people 10,000miles away in Japan.
These waves, which are generatedfrom a major disturbance to the water surface, are known as tsunami. (Mostscientists don't like the popular name "tidal wave" because tsunami havenothing to do with the tides. However, tsunami sometimes surge ashore likea huge, fast-moving tide rather than breaking like a classic surfing wave.)
Tsunamican travel at around 400 mph in deep water. When they reach shallow waterthey slow down, and that's when the real danger begins. The front of thewave slows first and the effect is like a pile-up on a freeway, with therear of the wave catching up to the front. The wave increases in heightfrom this bunching effect. The final height of the wave depends on severalfactors, but the shape of the sea floor has the greatest impact. Estuaries,harbours, cliffs, reefs, and the topography of the continental shelf allplay a role.
For a typical shoreline,the final tsunami height is usually about three times its height in deepwater, but in some locations the ratio (known as "run-up factor") reaches40. In other words, a 1-foot wave in deepwater can amplify to a 40-footwave at a shoreline that is exceptionally vulnerable to tsunami, as aresome parts of Hawaii.Tsunamican travel at around 400 mph in deep water. When they reach shallow waterthey slow down, and that's when the real danger begins. The front of thewave slows first and the effect is like a pile-up on a freeway, with therear of the wave catching up to the front. The wave increases in heightfrom this bunching effect. The final height of the wave depends on severalfactors, but the shape of the sea floor has the greatest impact. Estuaries,harbours, cliffs, reefs, and the topography of the continental shelf allplay a role.
For a typical shoreline,the final tsunami height is usually about three times its height in deepwater, but in some locations the ratio (known as "run-up factor") reaches40. In other words, a 1-foot wave in deepwater can amplify to a 40-footwave at a shoreline that is exceptionally vulnerable to tsunami, as aresome parts of Hawaii.
Splashdown
If an asteroid collides with the Earth there is a good chance it will hitan ocean, simply because two-thirds of the Earth's surface is covered bywater. A gigantic explosion occurs and the asteroid is pulverised and vaporised,along with a huge volume of water. This creates a crater in the water surfacethat quickly fills. The filling process generates a series of tsunami thatradiate across the ocean. The effect is similar to a pebble thrown intoa pond, though with a 50,000-mph impact, we're not talking ripples here.
Based on NASA estimates,about once every 2,000 years an asteroid with a diameter of about 100 yardscan be expected to hit one of Earth's oceans. Larger asteroids collidewith the Earth much less frequently -- a 500-yard rock from space mighthit an ocean once every 80,000 years and a 1,000-yard (1 k) asteroid perhapsonce every 200,000 years.
Atomic bombs and oceanimpacts
The largest aboveground H-bombtest by the United States was like a firecracker compared to an asteroidimpact. That "Bravo" explosion at Bikini Atoll in 1954 was equivalent tofifteen megatons (million tons) of TNT but was only about one-thousandthof the energy of a 500-yard asteroid moving at 50,000 mph.
The Bikini Atoll H-bomb testsenabled scientists to develop computer models of the destructive effects(on shipping) of explosions at the water surface. In the early 1990s thesemodels were applied to asteroid impacts. Initial results suggested thateven relatively small impacts could pose a grave tsunami threat over largeareas of ocean.
More recent modelling indicatesthat the tsunami generated by an asteroid impact tend to dissipate, ordie out, rapidly (the computer program, developed by Sandia National Laboratories,accurately predicted the consequences of the plummet of Comet Shoemaker-Levy9 into Jupiter in 1994).
According to this work, a500-yard-diameter asteroid is predicted to generate a water crater nearly3 miles in diameter. At a distance of 10 miles from "ground zero" the resultingdeepwater tsunami will be about 200 yards high, but by the time the wavehas travelled 100 miles it will be reduced to a height of about 14 yards.After 1,000 miles it will have dropped to less than 1 yard in height. Dueto the amplification in shallow water, however, this size tsunami couldstill become a 120-foot wave at a vulnerable shore.
Extra hazard to coastal areas
Due to the extra hazard of tsunami,locations such as Hawaii are at much greater risk from asteroid impactsthan inland areas. Rough calculations suggest that a coastal location witha typical tsunami run-up factor of three has about three times the riskof devastation from an asteroid-generated tsunami than the risk of a directblast to an inland location. Locations with an extreme tsunami run-up factorof 40 have about 70 times the risk compared with an inland location.
People in these vulnerablelocations need not lose sleep, however, because the odds of a major asteroid-generatedtsunami in any one year are about one in 200,000. On the other hand, asastronomer Duncan Steel has pointed out, asteroid impacts don't run toa timetable like busses.
The estimate of impact tsunamirisk is based on the limited search for Near Earth Asteroids carried outso far and assumes that impacts are randomly distributed in time. Thereis some evidence that impacts may come in clusters (some busses seem todo the same). If this is the case, then it is well worth finding out ifwe are approaching the next barrage so that coastal areas can be betterprepared.
Climate disruption
The comparison between coastaland inland locations is not entirely fair because the biggest danger froman asteroid impact is not from the direct blast but from the after-effects.In particular, the temporary cooling of the Earth due to huge quantitiesof dust released into the atmosphere from a land impact can disrupt cropproduction and lead to global starvation.
The giant plumes from theJupiter impact of Comet Shoemaker-Levy 9 clearly showed how a comet orasteroid tunnels through the atmosphere and creates a temporary chimney.This draws the impact debris into the upper atmosphere. Scientists areonly beginning to understand this effect in the case of an impact intoEarth's oceans.
An ocean impact by a 500-yard-diameterasteroid will vaporise about 20 cubic miles of water. At first sight thisappears to be insignificant since it is less than one tenth of the totalamount of water that evaporates from the world's oceans every day (assuming1 inch of rain over 10 percent of the Earth's surface each day).
Scientists caution, however,that an ocean impact would send the water vapour high into the atmosphere,compared with the lower atmosphere, or troposphere, in the case of evaporation.The upper stratosphere is normally extremely dry and the effects of a suddeninjection of a large quantity of water vapour are simply unknown. Othereffects of concern are greenhouse warming (water vapour is a strong greenhousegas) and ozone depletion. Unlike evaporation, an ocean impact would sendsalt (sodium chloride) into the air. The chlorine in the salt may affectupper atmosphere ozone levels in the same way as chlorofluorocarbons.
The same impact on land wouldpulverise an equivalent amount of rock (20 cubic miles -- about 1,000 timesthe volume of the asteroid) and send much of it into the upper atmosphere,where it would circulate around the globe and disrupt agriculture for manymonths.
A lesson from violent volcanoes
In 1815 a volcano on the Indonesianisland of Tambora exploded and produced a crater similar in size to thatfrom a 500-yard asteroid. About 20 cubic miles of ejecta was released (forcomparison, the Mount St. Helens explosion in 1980 released about a quarterof a cubic mile of ejecta).
In the case of Tambora, ithas been estimated that 10,000 people died directly from the explosionand 80,000 more died in the region from indirect effects, such as starvation.In addition, the ash is thought to have caused the "year without a summer"in 1816, when there were widespread crop failures across North America.The final death toll was probably in the hundreds of thousands. A similarevent today might kill millions.
Because of the chimney effect,an asteroid impact is much more efficient at sending dust into the upperatmosphere than a volcanic explosion, and the climatic disruption is probablymuch greater with an asteroid impact. Even so, the events of 1815 serveas a clear warning of the global danger from land impacts by asteroids.
With much less dust releasedinto the atmosphere, an ocean impact will have very different, and perhapsless damaging, effects than a land impact. If an asteroid struck thickice formations, such as Antarctica or the extensive ice sheets of the lastIce Age, the result would likely be similar to a water impact.
It's possible that our specieshas been saved from extinction several times because a large asteroid hitthe ocean or ice rather than the land. Every million years or so it canbe expected that a mile-wide asteroid will hit the Earth. A land impactwould probably cause severe climatic disruption and regional extinctions.Ifthe global effects of an ocean/ice impact are less severe than one on land,then the impact by a mile-wide asteroid into the ocean might not be ashazardous to life.
Evidence of ocean impacts
Past impacts with water or iceare very difficult to detect, because they leave very little evidence.One such impact is known to have occurred in the South Pacific Ocean, nearChile, about 2 million years ago. This event -- known as "Eltanin" afterthe ship that discovered the deposits -- involved an asteroid between 1and 3 miles in diameter that would have created a water crater at least40 miles across. Tsunami would have swamped coasts around the Pacific andwould even have reached some Atlantic coastlines. Assuming a typical run-upfactor of three, the coast of Chile would have been inundated by 250-yard-hightsunami. Likely results for other locations: Hawaii 90-yard tsunami (probablyhigher due to the greater run-up factor); California, 60 yards; Japan andAustralia, 25 yards; New Zealand; 120 yards.
Despite this presumed destructionto coastal areas, there is no evidence of global climate change or regionalextinctions around this time, when our early ancestors, Australopithecus,were roaming Africa. We don't know whether they would have been wiped outif the Eltanin asteroid had struck land in South America or Africa, insteadof splashing into the ocean. To solve that puzzle, to understand whichtype of impact most threatens our existence, we need a much better understandingof the consequences of asteroid impacts. -
61. What is the worldÂ’s largest desert?
The Sahara Desert in northern Africa is more than 23 times the size of southern CaliforniaÂ’s Mojave Desert. [Several readers have e-mailed to suggest that arid Antarctica technically tops this category; true, some researchers put it there, but most lists of deserts don't include it.]
62. Which planet has more moons, Earth or Mars?
Mars has two satellites, Phobos and Deimos. The Earth has only one natural satellite, but it's the Moon. The outer planets have lots of Moon, most of them found fairly recently and leading to the possibility that scientists might one day need to redefine what it means to be a moon.
63. What is the worldÂ’s deepest lake?
Lake Baikal in the south central part of Siberia is 5,712 feet (1.7 kilometers) deep. It's about 20 million years old and contains 20 percent of Earth's fresh liquid water.
64. What is the origin of the word "volcano"?
It derives from Vulcan, the Roman god of fire.
65. How many minerals are known to exist?
There are roughly 4,000 known minerals, although only about 200 are of major importance. Approximately 50-100 new minerals are described each year.
66. What is the total water supply of the world?
The total water supply of the world is 326 million cubic miles (1 cubic mile of water equals more than 1 trillion gallons).
67. What is the worldÂ’s largest island?
Greenland covers 840,000 square miles (2,176,000 square kilometers). Continents are typically defined as landmasses made of low-density rock that essentially floats on the molten material below. Greenland fits this description, but it's only about one-third the size of Australia. Some scientists call Greenland an island, others say it's a continent.
68. Where are most of EarthÂ’s volcanoes?
The most prominent topographic feature on Earth is the immense volcanic mountain chain that encircles the planet beneath the sea -- the chain is more than 30,000 miles (48,000 kilometers) long and rises an average of 18,000 feet (5.5 kilometers) above the seafloor. It is called the mid-ocean ridge and is where Earth's plates spread apart as new crust bubbles up -- volcanic activity. There are more volcanoes here than on land. The spreading, however, leads to scrunching when these plates slam into the continents. The result: More volcanoes and earthquakes in places like California and Japan.
69. What volcano killed the most people?
The eruption of Tambora volcano in Indonesia in 1815 is estimated to have killed 90,000 people. Most died from starvation after the eruption, though, because of widespread crop destruction, and from water contamination and disease.
70. Were Earth and the Moon separated at birth?
Not quite. But leading theory holds that our favorite satellite was carved partly from Earth shortly after the Earth formed. A Mars-sized object slammed into our fledgling planet. The impactor was destroyed. Stuff flew everywhere and a lot of it went into orbit around Earth. The Moon gathered itself together out of the largely vaporized remains of the collision, while Earth hung in there pretty much intact. -
redefine what it means to be a moon.
In the old days of astronomy, before Galileo, there was just the Moon. Then scientists had to accept the clear and visible evidence of four objects orbiting Jupiter, satellites the master saw through a crude telescope in 1610.
Things have only grown more complex, especially of late.
With a spate of discoveries in the past three years, the number of known moons in the solar system has jumped to 118 as of this writing. That figure won't stand long. Astronomers expect the tally to double, at least, in the next few years. Most won't be surprised if it eventually triples. And that's not counting the small stuff -- boulders the size of football stadiums and countless smaller rocks that are surely trapped in orbit around the big outer planets.
Meanwhile, the complexity of moon types and behavior grows with the tally, and astronomers are struggling to sort out what it all means.
Several interviews with moon hunters and top theorists reveal that the definition of a moon is not clear and that there has been almost no discussion, professional or casual, about whether there should be any lower size limits set to separate real moons from miniature imposters. And nobody is in a rush to do anything about it.
Orbiting rocks and atoms
Last month, astronomers announced they'd found the smallest known satellite, a moon just 0.62 miles (1 kilometer) in diameter orbiting Jupiter. It is one of dozens of small moons that behave strangely. Most go backwards compared to the orbits of the larger Galilean moons. Some take long, elliptical paths and stray far above and below the planet's plane of rotation. Few are round.
Saturn, Uranus and Neptune all have similar satellites.
Other configurations are more complex. Saturn's rings contain myriad chunks of ice and rocks that scientists don't consider moons. Yet embedded in the rings are distinct moons. Size -- and the ability to be noticed -- has so far played a role in being designated a moon.
Yet some moon-like objects are so small they are invisible. Hydrogen atoms at the outer fringes of Earth's atmosphere orbit the planet in an arguably moon-like manner.
"We don't call those satellites," says Alan Stern of the Southwest Research Institute (SwRI), making a firm delineation between moon and non-moon at least at the very lower end of the size spectrum. Dust grains, too, are out, Stern says. From there on up, however, nobody has thought much about where to draw the line, if at all, on what constitutes a moon.
"There is no accepted definition," Stern said.
So what would Stern call a 6-inch rock orbiting a planet? "I would call it a 6-inch rock." But, he acknowledges, "It's technically a satellite."
By that strict definition, there could be thousands of moons in our solar system, or millions if you count the debris in Saturn's rings. Nobody is proposing such an approach. Stern thinks it might be useful to create a separate category called "minor moons" to distinguish the small stuff from what is conventionally thought of as a moon.
Stern's suggestion was made to this reporter and is not an official proposal, but someone might need to propose something official pretty soon. NASA's Cassini spacecraft, due to arrive at Saturn next year, may force the issue.
For now, the smallest known satellite of Saturn is Pan, at 12.4 miles (20 kilometers) wide. Pan sits within Saturn's rings and was spotted in photos taken by the Voyager spacecraft.
The Voyager survey was incomplete, says Joe Burns, a Cornell University mathematical theorist and astronomer who is on the Cassini imaging team. Cassini will probably find much smaller moon-sized rocks in Saturn's rings, Burns said, and "no jury has voted" on whether to call these imminent discoveries moons or not.
"I think we'll have to confront that," he said.
Rich vernacular
When humans first put hunks of fabricated metal into orbit around Earth a few decades ago, astronomers needed to differentiate them from stuff that was already in space, so the term natural satellite came into use. In hindsight, it might not have been an overly inspired choice of words.
"I believe that the public is often confused when the term 'satellite' is used," said Matthew Holman, an astronomer at the Harvard-Smithsonian Center for Astrophysics who is a co-discoverer of three moons around Neptune. "The public normally equates 'satellite' with artificial satellite.'"
From a lay person's perspective, Moon terminology has only become more obscure.
Astronomers have developed a loose classification system that roughly separates moons into three types based on size and distance from their host planet: irregular moons, regular moons, and inner moons (sometimes called ring moons).
Irregular moons
Irregular moons are of unknown origin. They might be captured asteroids or comets, or perhaps they're pieces of young planetary hopefuls that didn't survive to orbit at the big table of nine, researchers believe. Many irregulars travel in packs that indicate they were once parts of larger objects.
The irregulars are typically small and orbit at great distances and often on odd trajectories. Their orbits are stretched and tilted in just about every way you can imagine. They soar high above and below the plane in which regular moons orbit. They come close to the planet and then zoom far away on elliptical trajectories. More often than not their orbits are retrograde -- opposite the direction of regular moons and of the planet's spin.
About the only thing they don't do is orbit in a plane perpendicular to that of the planet's orbit. Research led by Burns, the Cornell mathematician, has shown that the Sun's gravity causes such an orbit to be unstable, so any object captured in one would crash into the planet or escape.
Most irregulars have probably been in orbit since their host planet was very young, which astronomers cite as a good reason to call them moons, despite their odd and varied behavior. Nobody knows how they got captured, however.
Burns said it is very difficult for a planet to capture a moon. Unless something slows an incoming asteroid or alters its trajectory -- like a highly improbable pass at just the right angle through an atmosphere -- it will either hit the planet or fly on past.
"If it comes from infinity, it's going to go back to infinity," he said.
Perhaps, Burns speculates, the irregulars ran into an extended envelope of gas that might have surrounded a giant planet shortly after its birth 4.5 billion years ago. That would explain why irregulars tend to be small, because a smaller object has more surface area in relation to its mass, and is more likely to be captured than a large object.
Scientists aren't sure how the giant planets formed, let alone what conditions were like around them back then. So figuring out moons will help astronomers understand planets, researchers agree.
Regular moons
While irregular moons define the outer orbital reaches of a planet's domain in space, the next region in is dominated by regular moons. Examples include Saturn's moon Titan and Jupiter's Galilean satellites: Io, Europa, Ganymede and Callisto.
These classic, large and round moons tend toward entirely stable, simple, nearly circular orbits. All move through a plane in space that is roughly equal to the planet's equatorial plane. This conformity leads theorists to believe the moons formed out of the same nebula of gas and dust that built the planet.
Other so-called regular moons were probably carved by collision. Our own Moon likely developed after a Mars-sized object slammed into Earth. Some Uranian satellites might have been formed by an impact that flopped the planet over on its side.
Pluto's moon Charon is thought to have been created by collision, too, says the SwRI's Stern, who leads NASA's New Horizons mission to study the planet and set for launch in 2006. Interestingly, the gravitational midpoint around which those two objects revolve is not inside Pluto, but instead out in empty space. Some researchers prefer to call this a binary planet system (others don't consider Pluto a planet at all).
The Pluto-Charon system is not unlike pairs of other rocks orbiting each other out there on the fringes of the solar system, a region known at the Kuiper Belt. The dancing Kuiper Belt Objects, so-called KBO binaries, often involve a primary object with a smaller satellite and further stretch usage of the word moon.
"The KBO binaries aren't rocks, they are worlds," Stern says. "In fact, most are large enough to be rounded by gravity and therefore mini-planets in their own right."
More than 30 asteroids are known to have moons, too.
Inner moons
Inside the orbits of the regular moons, things get crazy.
Inner moons, sometimes called ring moons because they often travel amidst other debris, are almost surely the youngest. They're also the most likely to disappear. Here's why:
Planets, especially the large ones, act like gravitational brooms, gradually clearing the solar system of comets. That's bad news for any moon close to the broom.
"It's more dangerous down there," says Kevin Zahnle of NASA's Ames Research Center.
If you are a moon, the odds of being hit by a comet grow the closer you are to your host planet. Zahnle imagines flies buzzing around a hunk of raw meat. Pretend your hand is a moon, and pass it a few feet from the meat: you might not be hit by a single fly. Pass your hand a couple inches from the meat, and many flies might hit it.
Making matters worse, orbital mechanics dictates that inner moons travel more swiftly than outer moons, so collisions are more fierce, making it less likely that a moon will survive a hit. "And if you're smaller to begin with, it's more precarious to begin with," Zahnle adds, because you don't have the self-gravity to survive an encounter.
All this means that the life of an inner moon is very unstable.
"These are the most ephemeral and are presumably young," Zahnle said. He suspects inner moons might be well less than a billion years old, but cautions that there are no data to support that view. More needs to be learned about the population of comets, he said, and how frequently they impact the giant planets.
So are these precarious little objects moons? Definitely, Zahnle said. He adds, however, that in a ring system, the smaller rocks are constantly running into each other, their movement governed more by collision than by traditional orbital mechanics. Zahnle would tend toward calling these things debris, not moons.
Outcast moons
Outside the traditional categories of satellites are two sorts of objects that really stretch definitions.
Ahead of and behind Jupiter are two packs of asteroids -- tens of thousands of them -- that orbit the Sun but are also gravitationally bound to Jupiter. Astronomers call them Trojan asteroids. They are technically satellites of Jupiter, some astronomers say, but others, including Burns, consider them mere companions to Jupiter.
"The one property that I think a satellite must possess to be a satellite is an orbit that encircles its planet," Burns said.
Earth, Mars and Neptune are each known to control one or more Trojan objects in similar fashion.
Earth has acquired a sort of enhanced Trojan, too. A rock called 2002 AA29 orbits the Sun while also carving a horseshoe-shaped path around Earth. Every few centuries it gets close enough to Earth to be considered more than a Trojan, becoming what astronomers now call a quasi-satellite.
To astronomers, all this is quite clear, but there might be room for further definition.
"I do not think a new classification [system] is needed," said Earth's quasi-moon co-discoverer Martin Connors of Athabasca University in Canada. "For technical purposes we may wish to define sub-categories."
A moon by any other name ...
Nobody has found more moons than David Jewitt of the University of Hawaii. Along with colleague Scott Sheppard, Jewitt's team has found three dozen satellites orbiting Jupiter and has more in the observational pipeline. Jewitt is not keen to redefine moon terms or set any lower size limit.
"To me, they're all natural satellites," he said. "Is a small dog not a dog because it is small?"
If there is some confusion now, Jewitt says, then that reflects the healthy progress of discovery, and greater clarity will be the ultimate result. Jewitt realizes, however, that from a public perspective there can be some "pain" associated with no longer being able to look satellites up in a textbook. "Many people are not comfortable with a world that changes quickly."
One thing that hasn't changed, not since well before Galileo's time: There is still only one natural satellite you can step outside and see with your naked eye, the one we call, simply, the Moon. -
71. How many lightning strikes occur worldwide every second?
On average, about 100. Those are just the ones that hit the ground, though. During any given minute, there are more than a thousand thunderstorms around the Earth causing some 6,000 flashes of lightning. A lot of it goes from cloud-to-cloud.
72. Are rivers alive?
Not in the traditional sense, of course. But like all living creatures, rivers have a life span. They are born, grow in size, and they age. They can even die during the span of geological time.
73. Can asteroids create islands?
Speculation has existed for decades that ancient asteroid impacts might create hot spots of volcanic activity, which could give rise to mountains that poke up through seas that didn't used to be there. There's no firm answer to this question, but a recent computer model suggested Hawaii might have been formed in this manner.
74. Is the state of Louisiana growing or shrinking?
Louisiana loses about 30 square miles (78 square kilometers) of land each year to coastal erosion, hurricanes, other natural and human causes and a thing called subsidence, which means sinking. Much of New Orleans actually sits 11 feet (3.4 meters) below sea level. Parts of the French quarter have sunk 2 feet in the past six decades. The city is protected by dikes, but all experts agree that storm tides from a direct hit by a major hurricane would breach the system and swamp much of the city. In 2000, the director of the U.S. Geological Survey, Chip Groat, said: "With the projected rate of subsidence, wetland loss and sea-level rise, New Orleans will likely be on the verge of extinction by this time next century."
75. How much would seas rise if the Antarctic Ice Sheet melted?
The Antarctic Ice Sheet holds nearly 90 percent of the world's ice and 70 percent of its fresh water. If the entire ice sheet were to melt, sea level would rise by nearly 220 feet, or the height of a 20-story building. Scientists know there's a melting trend underway. The United Nations has said that in a worst-case scenario -- depending on how much global air temperatures increase -- seas could jump 3 feet (1 meter) by 2100.
77. Is ice a mineral?
Yes, ice is a mineral and is formally described as such in Dana's System of Mineralogy.
77. What is the softest of all minerals?
Talc is the softest of minerals. It is commonly used to make talcum powder.
78. What is the hardest of all minerals?
The one that becomes emotionally useless after a divorce but still retains monetary value.
79. How are colors produced in fireworks?
Mineral elements taken from Earth provide the colors. Strontium yields deep reds, copper produces blue, sodium yields yellow, and iron filings and charcoal pieces produce gold sparks. Bright flashes and loud bangs come from aluminum powder.
80. Does Earth have the worst weather in the solar system?
Right now, it's the worst that most humans I know ever experience. But there's lots of wilder weather elsewhere. Mars can whip up hurricane-like storms four times bigger than Texas. Dust storms on the red planet can obscure the entire globe! Jupiter has a hurricane twice the size our entire planet, and it's lasted for at least three centuries (another storm on Jupiter is even bigger). Venus is a living hell, and Pluto is routinely more frigid than the coldest place on Earth (though may change one day, and Pluto may in fact become the last oasis for life). -
a recent computer model suggested Hawaii might have been formed in this manner.
It's bad enough when, every few million years, an asteroid rocks our planet. It's worse if the impact triggers regional or global volcanic activity, which is not only hazardous to nearby plants and animals but can choke Earth's atmosphere with deadly gases for months or years.
But there's also a possible bright side, like the birth of nice places like Hawaii.
For more than three decades, scientists have explored the question of whether an asteroid impact could cause significant volcanic eruptions, hot spots that spring up out of nowhere and create new landforms or rearrange old ones. The process might have given birth to the Hawaiian islands, for example. The idea of linking space rocks and lava goes back to at least the 1960s, and in recent months the debate has heated up like a volcano ready to erupt.
Though no firm answers have emerged, controversial computer modeling in recent years has shown what might happen, and why.
Old and buried
Andrew Glikson from the Australian National University makes a living by hunting for signs of ancient impact craters, many of which are not readily visible, some of which are buried under oceans that didn't used to be where they are now.
In several recent papers, Glikson maintains that the large craters found so far on Earth only account for about one-fifth of the actual number of major impacts predicted over the past 3.8 billion years. These impact predictions are based on a number of factors, including the vast numbers of craters on the Moon, which don't disappear on the geologically dead and atmospherically challenged satellite.
During these billions of years it is likely that there were at least 10 impacts producing craters more than 125 miles (200 km) in diameter and 30 impacts producing craters more than 60 miles (100 km) in diameter, Glikson figures. And he argues that at least 50 percent of these impacts would have struck locations in ancient oceans where the Earth's crust was much thinner than continental crust and, in particular, some 10 percent would have struck the thin crust adjacent to mid-ocean ridges.
A volcanic eruption is much more likely to occur if an impact occurs at one of these sites and, paradoxically, evidence of the impact is likely to be buried under the eruption and lost forever if that area is later folded, or subducted, into the Earth's crust.
But Jay Melosh, a crater expert from the University of Arizona, doubts this and other links between asteroids and volcanoes. Melosh presented his views last July at a conference on catastrophic events in Vienna.
"There is not a single clear instance of volcanism induced by impacts, either in the near vicinity of an impact or at the antipodes (opposite side) of the planet," Melosh concluded. "The possibility of impact-induced volcanism must therefore be regarded with extreme skepticism."
Researchers who are independently working on various impact mechanisms say Melosh's reasoning is flawed.
Hermann Burchard is a mathematician at from Oklahoma State University. He notes that there are several examples where either a volcanic eruption is speculated to be associated with a known impact or an undiscovered impact is speculated to be associated with a major eruption. Again the problem is that such eruptions tend to obliterate evidence of an impact.
Rocking the other side of the planet
Mark Boslough and his colleagues at Sandia National Laboratories have modeled asteroid impacts. In a 1996 paper, they predicted that the seismic energy from an impact travels through the Earth and is strongly focussed at the antipode to the impact, near the boundary of the crust and the hot, molten mantle.
This, they argue, generates instability in the upper mantle that can produce a "hot spot" under the surface, like the one that continues to form the Hawaiian Islands. They also claim that geologists have no satisfactory explanation for the generation of hot spots by other means, other than that they arise "spontaneously."
Melosh expressed skepticism about the focussing idea after calculating that the seismic energy delivered to the antipode would be insufficient to melt the rocks. Boslough counters that melting is not needed to generate an instability -- the increased temperature of the region may be sufficient to trigger the start of a hot spot.
Clues on the Moon
Dallas Abbott from Columbia University, New York has taken a different approach to the whole question.
Using terrestrial evidence and crater evidence from the Moon, which retains a record of bombardment going back nearly 4 billion years, Abbott has analyzed the timing of large impacts compared with major volcanic eruptions, or mantle plumes.
She found a strong correlation between the two and speculates that large impacts strengthen existing mantle plumes. She describes the ancient and dormant Deccan Traps volcanism, an area that is presently part of India. At the time of the Chicxulub asteroid impact, which occurred in Mexico 65 million years ago and likely led to the demise of the dinosaurs, the Deccan Trap region was near the antipode of the impact.
Others have suggested this coincidence could be possible evidence that impact antipode effects initiated the Deccan Traps.
However, Boslough says the Deccan Traps would have been several thousand kilometers away from the antipode to Chicxulub. Abbott says the Deccan Traps were active well before the Chicxulub impact, and so could not have been initiated by that event, but she observes that the Deccan plume was strongest immediately after the impact and this phase lasted less than one million years.
At the least, it appears to be a strange coincidence.
Despite advances in computer modeling, there is no clear physical evidence of a link between space rocks and lava, but the models are coming up with mechanisms by which an impact could cause, or at least speed up, a volcanic eruption.
And proponents of the idea are quick to point out that geologists have not come up with a better explanation for how the Earth's hot spots got started. -
81. Where are the highest tides?
In Burntcoat Head, Minas Basin, part of the Bay of Fundy in Nova Scotia, tides can range 38.4 feet (11.7 meters). The bay is funnel shaped -- its bottom slopes upward continuously from the ocean inlet. The result is an extreme "tidal bore," a wave-like phenomenon at the leading edge of the changing tide. Bores in Fundy can travel up feeder rivers at 8 mph (13 kph) and be more than 3 feet (1 meter) tall.
82. Where is the world's only equatorial glacier?
Mt. Cotopaxi in Ecuador supports the only glacier on the equator.
83. What is the largest lake in North America?
Lake Superior.
84. What's the deadliest hurricane to ever hit the United States?
A Category 4 hurricane hit Galveston, Texas in 1900 and killed more than 6,000 people (read about the history of it here). The next closest death toll was less than 1,900 from a 1928 Florida hurricane.
85. What is the longest mountain chain on Earth?
The Mid-Atlantic Ridge, which splits nearly the entire Atlantic Ocean north to south. Iceland is one place where this submarine mountain chain rises above the sea surface.
86. How much gold has been discovered worldwide to date?
More than 193,000 metric tons (425 million pounds). If you stuck it all together, it would make a cube-shaped, seven-story structure that might resemble one of Donald Trump's buildings. First you'd have to find all those rings that have gone down the drain.
87. What are the two major gold-producing countries?
South Africa produces 5,300 metric tons per year, and the United States produces more than 3,200 metric tons.
88. What North American plant can live for thousands of years?
The creosote bush, which grows in the Mojave, Sonoran, and Chihuahuan deserts, has been shown by radiocarbon dating to have lived since the birth of Christ. Some of these plants may endure 10,000 years, scientists say. If only they could talk.
89. On average, how much water is used worldwide each day?
About 400 billion gallons.
90. Is Saturn the only ringed planet?
Saturn has the most obvious rings. But Jupiter and Neptune both have subtle ring systems, [as does Uranus, readers reminded me]. And even Earth may once have been a ringed planet, the result of some space rock's glancing blow. -
And even Earth may once have been a ringed planet
Earth may once have been surrounded by temporary rings of debris, much like Saturn, according to a new computer model that finds the rings might have cast parts of the planet into a twilight glow all day long.
The idea is not new, but the fresh modeling adds weight to the plausibility of an asteroid impact kicking up a sea of orbiting debris, and it considers how the rings would have cooled Earth's climate.
The new model, based on Saturns B-ring scaled down to Earth-size, was produced by Peter Fawcett of the University of New Mexico and Mark Boslough of the U.S. Department of Energys Sandia National Laboratories. It is based on climate models that had already been developed.
The scientists said a ring might form with a glancing blow, in which a space rock and the debris it carves from the planet ricochet into the atmosphere.
An expanding vapor cloud causes some of the debris to go into orbit. Over time, it collapses into a plane that matches Earth's equator. The ring then lasts from about 100,000 years to perhaps 1 million years at most.
Fawcett told SPACE.com the debris ring would have cooled the planet by blocking or reducing the amount of sunlight received in the tropics and subtropics. The rest of the planet would cool, too, because less heat would be transported from tropical regions to higher latitudes. That would mean fewer storms farther north.
The work is speculative, the researchers say, but there is some evidence they might be on the right track.
Geologic records reveal a layer of melted meteorite material thought to be associated with an asteroid impact 35.5 million years ago. Some 100,000 years of cooler global temperatures followed.
"This cooling is longer than one would expect from a large impact alone, so we hypothesized that a temporary ring might have formed," Fawcett said. "The jury is still out on this though."
Had there been any humans on the planet to survive the impact and witness the rings, it's hard to say exactly what they would have seen. But Boslough has some ideas, based on an assumption that the rings would have been semi-transparent, like Saturn's.
"For a person in the shadow of a reasonably opaque ring, it would be dark like twilight or a heavy overcast," he said. "The ring would be scattering light in addition to blocking it. I think the most spectacular view would be after sunset or before sunrise, when the sky is dark but parts of the sunlit ring would be brightly visible in the sky." -
91. What is the highest, driest, and coldest continent on Earth?
That would be Antarctica.
92. At what depth do most earthquakes occur?
Most are triggered less than 50 miles (80 kilometers) from the EarthÂ’s surface. Shallower earthquakes have more damage potential, but a temblor's destruction also depends largely on rock and soil conditions as well as building methods.
93. Where are the oldest rocks on Earth found?
Since the ocean floor is being continually regenerated as the continental plates move across the EarthÂ’s surface, the oldest rocks on the ocean floor are less than 300 million years. In contrast, the oldest continental rocks are 4.5 billion years old.
94. What percentage of the worldÂ’s fresh water is stored as glacial ice?
About 70 percent. And if you had to replace it all, you'd need 60 years of the entire globe's rainfall, and then you'd have to figure out a way to freeze it all.
95. What is the largest alpine lake in North America?
Lake Tahoe on the California-Nevada border has a 105,000-acre surface, holds 39 trillion gallons of water, and is almost 1,600 feet (488 meters) deep.
96. Have there always been continents?
Not as we know them today. Many scientists figure Earth began as one huge continent -- dry as a bone. Water was delivered in comets, the thinking goes, and the oceans developed. Much more recently, all the world's landmasses were huddled into one supercontinent called Pangaea. It began to break up about 225 million years ago, eventually fragmenting into the continents as we know them today.
97. How much volcanic ash can fall in a day?
I can only give an example. During the 9-hour period of most vigorous activity on May 18, 1980, Mount St. Helens dumped more than 540 million tons of ash over an area of more than 22,000 square miles (56,980 square kilometers). It was the most destructive volcanic eruption known to occur in the United States. Fifty-seven people were killed by the eruption including USGS scientist Dr. David Johnston, who was at a monitoring site 5 miles (8 kilometers) from the volcano. An estimated $1 billion damage was caused by the eruption, through mudflows and landslides as well as what fell from the sky.
98. What is feldspar?
A better question might be, "Who but a geologists could love feldspar?" It happens to be the most common mineral in Earth's crust. But I couldn't find anything about it that most of us really need to know.
99. What are the most extreme locations in the United States, compass-wise?
This one is a bit tricky, and as it turns out three or even four of the answers may catch you off guard. The westernmost point is the aptly named West Point of Amatignak Island, Alaska. The northernmost point is Point Barrow, Alaska. The southernmost point is the southern tip of the island of Hawaii. The easternmost point -- go ahead, take a guess! -- is Pochnoi Point at Semisopochnoi, Alaska. Huh? Look at a world map. The tip of the Aleutian Islands lies on the other side of the 180-degree longitude line --- the International Dateline -- putting Pochnoi Point barely but officially in the Eastern Hemisphere.
100. If you were to arrange Earth, the Moon and Mars like Matryoshka nesting dolls, how would they be ordered?
Mars would nest inside Earth, and the Moon would fit neatly inside Mars. Earth is about twice as big as Mars, which is about twice as big as the Moon.
101. Will Earth always be here?
Astronomers know that over the next few billion years, the Sun will swell so large as to envelop Earth. If we're still here, we'll probably fry and the planet will be vaporized. There's a chance, however, that the changing mass of the Sun will cause Earth to move into a more distant and pleasant orbit. One mathematical calculation shows it would be theoretically possible for humans to engineer such a move before it's too late.