An Ancient Universe: How Astronomers Know the Vast Scale of Cosmic Time

MARTIAN METEORITE

Millions of years ago, an enormous impact (a large chunk of rock or ice hitting Mars) blasted parts of the planet out into space. After a long time, some of these pieces of Mars landed on Earth. This Martian rock was found in Antarctica in 1984. We know it came from Mars, because scientists have found pockets of air inside, and this air is exactly like Mars' atmosphere and not like Earth's. Such chunks from space (called meteorites) allow astronomers to study the chemical makeup of other parts of the solar system. (Courtesy NASA Johnson Space Flight Center.)

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