Three billion years ago, Earth was a very different place.
No-one knows when life first established a firm foothold on Earth. Ask around in the scientific community, though, and you’ll probably hear that the surface of early Earth, before about 3.8 billion years ago, was too hostile an environment for even a lowly microbe to set up shop.
The main problem, as the conventional argument goes, was that between around 4.1 and 3.8 billion years ago, Earth was constantly being bombarded by comets and asteroids. The disastrous effects of these impacts would have rendered the Earth’s surface uninhabitable.
Not necessarily so, say a team of astrobiologists who ...November 27, 2000 • Posted by: Shige Abe • Report issue
Nathalie Cabrol, who has spent many long hours poring over images of Mars taken from orbiting spacecraft, believes those images contain convincing evidence that lakes were present on Mars in the recent past.
“Recent” requires some definition when you’re talking to geologists. In this case, it means some time in the past half a billion years or so, give or take a couple hundred million. There are no lakes present on the Martian surface today.
Cabrol, a member of the NASA Astrobiology Institute (NAI) and a principal investigator with the SETI Institute, works at NASA’s Ames Research Center in ...November 27, 2000 • Posted by: Shige Abe • Report issue