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All life (as we know it) depends on carbon. But most models of Earth's formation can't explain how the crust has enough carbon to support life. So where did it all come from?
A colossal smashup with a Mercury-like protoplanet some 4.4 billion years ago, suggest researchers from Rice University and Woods Hole Oceanographic Institution in a new study published in the journal Nature Geoscience.
Most scientists agree that about 4.5 billion years ago, Earth was covered with hot magma, and as it cooled, most of the heavier metals near the surface sank deep into the planet. Iron alloys bonded with carbon and sulfur, pulling both into the Earth's core, and any remaining carbon would have vaporized into space from the extreme heat, argue the scientists. The only way to keep carbon and sulfur near the surface is to bring some from a planet that formed differently, they say.
A different story reported last week that scientists have identified fossilized stromatolites that date to 3.7 billion years ago, or 700 million years after the worst day ever for the young Earth.
(Score: 4, Interesting) by Immerman on Friday September 09 2016, @04:04PM
Indeed. Within solar systems, where asteroid impacts regularly generate planetary fragments that can collide with other planets after only months or decades in space it seems almost inevitable. Sure, the energies involved in the initial impact and later reentry to another planet would tend to kill almost everything, but especially larger fragments would have a decent chance of more durable organisms surviving. Even some relatively complex life like tardigrades ("water bears") have been shown to be capable of surviving extreme conditions for prolonged periods, even being frozen solid, or exposed to the vacuum and radiation of space, without lasting harm. Effectively "dying" and then resurrecting themselves and performing some truly astounding genetic repairs once they're someplace more hospitable again.
Panspermia between stars though seems far more unlikely - no normal impact would fling planetary fragments free of the host star. It's possible that gravitational slingshots would occasionally fling a fragment free, but that will be comparatively rare, and you'd generally be talking about thousands of years of transit time even if it happened to depart on a path that would take it to the nearest star. Even at near absolute zero that's a long time for a cryogenically preserved organism to be bombarded by radiation, though a sufficiently large fragment might shield its core well enough.
There's also the case where a life-hosting star goes (super)nova, flinging planetary fragments throughout the resulting nebula, but those energies make the infernos of asteroid impacts look birthday cake candles. Still, I suppose big enough fragments would shield their cores from the worst of it, and then you've got a huge cloud of life-bearing fragments that other stars could pass through.
The only other option that springs to mind is intelligent life spreading life intentionally. Sending colony ships between stars would be phenomenally expensive and invokes Fermi's Paradox, but tiny "seedships" designed to cross between stars in a few decades or centuries and deliver a genetically rich living payload of hardy and versatile microorganisms capable of jump starting life on a promising planet? Those could be comparatively cheap and easy to send out by the bushel. Regardless of whether they just think life is worth spreading, or have ambitions of one day colonizing the seeded worlds, it seems like an endeavor many civilizations might engage in. Maybe there's a reason tardigrades are so durable...