70 Asteroids and Meteorites

In addition to comets, two other relatively small bodies can be found floating around the solar system. They are known as asteroids and meteorites. Asteroids are smallish bodies that orbit the sun, mainly in the area between Mars and Jupiter. Though not large enough to be thought of as planets, asteroids can range from the size of a small boulder to several hundred miles in diameter. They are rocky bodies made up of various metals and other substances. Now and then something will jar an asteroid out of its orbit. Then it may approach or—very rarely—hit Earth.

Meteorites are also small, rocky bodies that have traveled through space. Some may be broken-off pieces of asteroids; some may be leftover chunks of comets. Meteorites are pieces of rock from space that actually hit our planet.

When these intruders make contact, what damage do they do? It all depends on their size and where they hit. Since Earth is mostly made up of water, a small meteorite falling into the Atlantic Ocean probably won’t harm anything. But some meteorites strike solid ground. A meteorite weighing about sixty tons once hit near a farm in southern Africa. Another huge one broke up in the air above Siberia in 1908. It destroyed trees in a twenty-mile area.

The damage from a huge fallen asteroid can be far worse. In eastern Mexico are the remains of a basin one hundred miles wide where an asteroid touched Earth 65 million years ago. Enough debris shot forth to block out the sun’s light for decades. When there was light again, all the dinosaurs had disappeared.

70 小行星与陨石

除了彗星之外，太阳系中还存在另外两种相对较小的天体，它们被称为小行星和陨石。小行星是围绕太阳运行的小型天体，主要位于火星和木星之间的区域。虽然小行星的体积不足以被视为行星，但它们的大小范围可以从一块小巨石到直径数百英里不等。它们是由各种金属和其他物质组成的岩石天体。偶尔会有外力使小行星脱离轨道，之后它可能会靠近地球，或者——非常罕见地——撞击地球。

陨石也是穿越太空的小型岩石天体。有些可能是从小行星上脱落的碎片；有些可能是彗星残留的碎块。陨石是从太空中落到我们星球上的岩石碎块。

当这些“入侵者”与地球接触时，会造成什么破坏呢？这完全取决于它们的大小和撞击位置。由于地球大部分是由水构成的，一颗小型陨石坠入大西洋可能不会造成任何危害。但有些陨石会撞击陆地。曾有一颗约60吨重的陨石撞击了南非南部的一个农场附近。另一颗巨大的陨石在1908年于西伯利亚上空解体，摧毁了20英里范围内的树木。

大型坠落小行星造成的破坏会严重得多。在墨西哥东部，有一个直径100英里的盆地遗迹，这里是6500万年前小行星撞击地球的地方。当时飞溅出的碎片足以遮蔽太阳光线数十年。当光线再次出现时，所有的恐龙都已经灭绝了。