Facts About Earth - I

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, lo aded 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.