Earthquakes, Mars

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 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 the 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.

Fate?

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.