> Knowing that there was life on earth as far back
> as we can go (3.4 billion years) and that at least
> one form of microorganism hasn't evolved in 2
> billion years seems to open up all sorts of
> possibilities to test--but that's as far as we can
> One possibility is that passing comets seeded and
> reseeded earth (primitive version), or that
> intelligent beings brought and/or nurtured
> (transformed) life from other origins numerous
> times (alien invaders version)--or, it just
> started up here (who knows when)
> spontaneously--perhaps multiple times.
> We are free to speculate. But until we go out and
> gather some evidence, we are no closer to
> establishing the reality of life in the
> universe--or even understanding the origin of
> life--than we ever were.
Understood, and I agree. They had a hard enough time going back even that far--most of Earth's really old rocks have been subducted into the crust. In fact, to get an accurate age of the Earth, the poor grad student assigned to the project was reduced to getting his hands on meteorites.
3.465 billion years ago is stunningly early, and yet it's not the oldest life found. They found bacterial remains in Australia dating back 4.1 billion years.
That's almost all the way to the birth of the solar system.
If life arose that early on a molten lava Earth, it really can't be that hard for it to get going (or, alternately, it landed here from somewhere else). So IMO the authors aren't really going out on a limb to suggest that life may be common.
Edited 1 time(s). Last edit at 21-Dec-17 16:26 by Aine.