Question

How do asteroids and meteorites relate to the origin and composition of the earth?

There are many types of meteorites with many different types of compositions, so I won’t go into each one. Early in the history of our galaxy, all of the material that would form the various parts of our solar system existed as molecules of gas and dust in what’s called a solar nebula. As this nebula spun, a disk formed and most of the material fell into the center of the disk to form the star. Some of it, however, began to accrete together and grow into early planets and asteroids. The composition of these bodies depended on where in the nebula they formed. For example, planets forming close to the sun could have more rocky and metallic material but could not have contained ices like the planets forming farther from the sun. Along with planets, smaller bodies like asteroids would have also formed and simply not grown large enough to be called planets. Their composition would also be governed by where they formed in the disk. Meteorites are rocks that have been blown off a parent body by an impact event and fall to Earth. They therefore would have the same general composition as the parent body. Most meteorites are thought to originate in the asteroid belt and therefore may be very good representatives of the early galaxy. Several have been found that came from the Moon or Mars. Early in the Earth’s formation, impacts by meteorites were very common, and they may have been able to contribute to the overall composition of Earth. That contribution now, however, is very minor. Zack Krug Doctoral Student in Geosciences, Penn State University
June 3, 2002