Facts about Earth

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.

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 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 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!

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. 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