It's hard to know exactly when or how life began on Earth; there are very few rocks and fossils left over from the planet's early days. The Earth has swallowed some of its crust, and water has worn away its surface. Now a team of researchers has discovered a place where early signs of life may be lurking. Unfortunately, it's some 250,000 miles away -- on the moon. NPR's David Kestenbaum reports for Weekend Edition Sunday.
Scientists estimate the Earth is about 4 and a half billion years old. Planets were just forming at the time, and the solar system was a chaotic place. Meteorites crashed into the Earth regularly. When they hit, bits of debris would have shot up into the air -- fast enough for some of it to escape Earth's gravity.
It's thought that the moon was orbiting much closer to the Earth then; it's possible it could have swept up some of the debris. A paper detailing that theory is being published in the astrobiology journal ICARUS.
The idea isn't unheard of, says Kestenbaum. Rocks from Mars have turned up on Earth. In the paper, co-author Guillermo Gonzalez, a physicist at Iowa State University, concluded that for every million grains of moon dust, there may be seven grains that came from Earth. And if scientists looked hard enough, there might even be a few pebbles or rocks around as well.
The moon's surface does preserve well, but it's also highly erosive, says Gonzalez. The constant rain of micrometeorites in a sense is sandblasting everything on the surface, he explains. A 1-centimeter rock would be turned to dust in about 10 million years.
The authors of the paper envision sending a robotic explorer--or even a human--to search the moon for evidence of what Earth was like billions of years ago. For now, scientists have to be content with studying the 800 pounds of rock and dust brought back during the NASA Apollo missions. Most of those samples have proven to be very ancient, between 3 billion and 4.6 billion old years old.