Scientists Say Canadian Bacteria Fossils May Be Earth’s Oldest

> If anyone could answer, I've always wondered how a hypothetical bacteria on an asteroid could survive impact with earth or any celestial body.

Thinking about it, my initial thought "part of the asteroid didn't get that hot" can't be right...

More likely [0], some components of the organism can remain intact after impact. Seeing papers like this one [1], where different components of a system can/do combine, or seeing one of the current theories for how mitochondria came to exist [2], makes me think extremely low probability combinations happen to workout sometimes. That, plus trillions of chances to happen.

[0] PhD, but not in astrobiology...

[1] http://www.cell.com/cell-host-microbe/pdfExtended/S1931-3128...

[2] https://en.wikipedia.org/wiki/Hydrogen_hypothesis

Such evidence does tend to support panspermia hypotheses, but I don't think it helps much to support arguments about the tolerances of conditions required for the origin of life.

Life itself is effectively "a chemical soup that maintains homeostasis to keep its reactions going." Once you have something that can do that, you'd somewhat expect to find versions of it in all sorts of insane places—a bit like how you'd expect to find humans in all sorts of insane places, given that we can invent things like spacesuits.

But getting from basic replicators to (homeostatic) life is the hard part, because those replicators don't have the "defences" life has against the environment. If it gets too hot or cold, they die; if it gets too dry or saline or acidic or nitrogenous or anoxic, they die; they probably even die if they get too much visible-range sunlight.

A large mass of replicators—presuming they have RNA and mutational asexual evolution already—could eventually be winnowed into a group that has adapted into a homeostasis "feature." But you would need to start with "a large mass" of them—and it's questionable where you'd get that, given that it's unlikely for any single one to survive. (Maybe they developed biofilm-production early on. Maybe they had viroids. Maybe they were just really, really prolific. But "they just managed" is pretty unlikely.)

It is a really interesting question. Up until relatively recently it was fairly difficult to culture 'dirt' bacteria. (something about them not growing in petri dishes) but now that we can, there is a really interesting experiment to run which is to take a quarter cup of soil as control, and a quarter cup in a container that you send up and attach to the outside of the ISS for a few weeks, then bring it back and culture them both to see what survived.

> It seems that whenever we consider conditions too extreme to support life, we find that it flourishes. From the hydrothermal vents of the Mariana Trench, where temps can reach 340 C and pressures of 1100 atmospheres to tardigrades surviving in the near vacuum of space

Tardigrades can survive in space, but they can't flourish there.

Rare Earth: Why Complex Life is Uncommon in the Universe by Ward and Brownlee is a fantastic read on the subject.

from the article :

>just 340 million years after the formation of the plant

Also when you consider that the earth was uninhabitable for most of those first few hundred million years. This was a time when our planet was still getting bombarded by asteroids and oceans would have boiled away into steam. Temperatures were hot and the surface was volcanic. It was barely habitable at this point.

That would would qualify as shortly by most estimates. Life began as soon as it was possible.