101 Amazing Facts

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101 amazing facts about the earth

The biggest earthquake, the largest desert, even how our planet sizes up — the answers are right here.
 
NASA's "Blue Marble" image of Earth, with the moon in the background, was created by combining many satellite images of the planet's surface and surroundings.
 

By Robert Roy Britt
SPACE.COM

July 22 — We live on a sphere of extremes and oddities. In fact it’s not really a sphere, but it is a wild planet, mottled with deadly volcanoes, rattled by killer earthquakes, drenched in disastrous deluges. But do you know which were the worst?

SOME OF EARTH’S valleys dip below sea level. Mountains soar into thin air. Can you name the lowest spot? The tallest peak? Do you know how far it is to the center of the planet or what’s there?

Where are the planet’s hottest, coldest, driest and windiest places?

The following list of Earth’s extremes and other amazing facts is presented in Q&A format, so you can cover the answers to test your knowledge of the home planet. Sources include the U.S. Geological Survey and the National Oceanic and Atmospheric Administration, with other Space.com reporting.

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 Earth’s 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 world’s 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 L.A. 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 with 365 days for Earth. Taking into account Mars’ different rotational time (see No. 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) an extra half-hour every day compared to you. Mars days are 24 hours and 37 minutes long, compared with 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 world’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 and 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 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 Mount 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! (Find out why.)

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, Calif., 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 kilometers per hour).

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 it were added 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 Hell’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 Earth’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 world’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 land masses contain the vast majority of the Earth’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 Earth’s total.

39. Which of Earth’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 world’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 vs. 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 Hollywoodlike 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 (tides on Mars?).

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 Earth’s surface consists of volcanic rock?
Scientists estimate that more than three-quarters of Earth’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 Earth’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 earthquake’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.

56. How much of Earth’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 kilometers per hour), recorded at Mount Washington, N.H., on April 12, 1934. But during a May 1999 tornado in Oklahoma, researchers clocked the wind at 318 mph (513 kilometers per hour). For comparison, Neptune’s winds can rage to 900 mph (1,448 kilometers per hour).

59. How much fresh water is stored in the earth?
More than 2 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.

61. What is the world’s largest desert?
The Sahara Desert in northern Africa is more than 23 times the size of southern California’s Mojave Desert.

62. Which planet has more moons, Earth or Mars?
Mars has two satellites, Phobos and Deimos. Earth has only one natural satellite, but it’s the moon. The outer planets have lots of moons, 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 world’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 world’s largest island?
Greenland covers 840,000 square miles (2,176,000 square kilometers). Continents are typically defined as land masses 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 Earth’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.

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 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 under way. 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.

76. 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 hurricanelike 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).

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 wavelike phenomenon at the leading edge of the changing tide. Bores in Fundy can travel up feeder rivers at 8 mph (13 kilometers per hour) and be more than 3 feet (1 meter) tall.

82. Where is the world’s only equatorial glacier?
Mount 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. 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. And even Earth may once have been a ringed planet, the result of some space rock’s glancing blow.

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 Earth’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 Earth’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 world’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 land masses 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 nine-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 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, compasswise?
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 east 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.

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