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 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 produce s 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?
Asteroid-generated tsunami
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 Earth’s land surface is desert?
About one-third.
57. What's the deepest place in the ocean?
The greatest k nown 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 f ar 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.
Saturday, May 3, 2008
Facts About Earth - V
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 exa mple, 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 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 scient ists 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 (tides on Mars?).
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 exa mple, 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 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 scient ists 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 (tides on Mars?).
Friday, April 25, 2008
Facts About Earth - IV
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 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.
Venus is almost as big as Earth. Despite sweltering heat at the surface, its clouds might support life, some scientists say.
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 landmasses 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 th e Earth's total.
39. Which of the 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 o f 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.
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 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.
Venus is almost as big as Earth. Despite sweltering heat at the surface, its clouds might support life, some scientists say.
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 landmasses 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 th e Earth's total.
39. Which of the 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 o f 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.
Facts About Earth - III
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) belowfont-style: italic' >, 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 ?
A laska 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 mater ials 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
The shore of the Dead Sea in the Middle East is about 1,300 feet (400 meters) belowfont-style: italic' >, 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 ?
A laska 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 mater ials 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
Thursday, April 24, 2008
Facts About Earth - II
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 .
Planet building
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 ma jor 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!
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 .
Planet building
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 ma jor 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!
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