Unrelated Life?

[Drooling Iguana]

Just a bit of idle wondering: Is it possible that life on Earth emerged independantly in two or more different regions at roughly the same time, and that the decendants of both may still be alive today? If so, and if the obvious stuff like the handedness of the DNA was the same, would we have any way of knowing about it?

[Cyborg Stan]

Very unlikely. IIRC, the DNA 'alphabet' encoding for the 20 amino acids we use are the same for just about every life form we see.

[GrandMasterTerwynn]

Just a bit of idle wondering: Is it possible that life on Earth emerged independantly in two or more different regions at roughly the same time, and that the decendants of both may still be alive today? If so, and if the obvious stuff like the handedness of the DNA was the same, would we have any way of knowing about it?

Yes. There are a number of ways at arriving at a self-replicating life-form. We've persuaded bacteria to use a 21st amino acid, proving that the 20 amino-acid rule is not so hard and fast. You can code for a few different amino acids than the twenty currenty in use by known Earthlife. You can also use DNA with more bases, or with different bases. You can also have RNA-based life, though RNA life would be so inefficient and error-prone that, if it still lives, it will be confined to niches well out of contact with current Earthlife.

The point of all this is that yes, there are a lot of ways where we could distinguish Earthlife not based on our biochemistry, though it would take careful analysis to pull off.

ADDENDUM:

A good discussion on this very topic can be had in the book Life As We Do Not Know It by Peter Ward.

[tharkûn]

Very unlikely. IIRC, the DNA 'alphabet' encoding for the 20 amino acids we use are the same for just about every life form we see.

The DNA 'alphabet' is the product of tRNA binding; it is possible (though I think highly unlikely) that the amino acid associations are determined by kinetic and thermodynamic minima rather than pseudo random arrangement. Certainly the redudancy (or lack thereof) is suggestive of adaptive selection at least at some level (this gets into a chicken or egg arguement).

A far better case is that we observe only left handed life; oppositely chiral lifeforms would have identical energies and kinetics to play with and thus all evidence shows a 50:50 distribution should exist for multple instantiations of life. Beyond that, there are numerous other ribose based acid/base pairs which behave similarly to A, C, T, G, and U and quite a large number of other possible amino acids (and many of these are used in limited quanty throughout nature). One would have to argue that not only did multiple instantiations of life all luck out on chirality, but that the only probable chemicals that can perform the requisite biological functions are the familiar set. Theoreticly possible, but not something I'd care to defend.

If so, and if the obvious stuff like the handedness of the DNA was the same, would we have any way of knowing about it?

See above. We know that many other possible amino acids exists, we know that you can even make other ribose based aromatic acid/base pairs; it seems to be a pretty big stretch that our set are the only viable ones.

However it is possible that independant life survives in some place where had a DAMN long head start before competition got to it; it would also have to be extremely isolated to prevent our strain of life from seeing it as a potential food source and leaving clues about metabolizing "exotic" biochemicals in large quantities. Possibly in some volcanoes or somesuch, but not bloody likely.