Amazing Earth Facts - IX

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 scientists 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? ).

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 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.