Puzzle 2 (Biology)

[shkrobius]

Finally, people invented the time machine. For technical reasons, it can go only 500 Myrs in the past and back. It has another unfortunate limitation: one can go back in time only to the same point in space. However, the Solar system moves through the Galaxy, and there is also cosmic expansion. Because the trajectory is somewhat chaotic, finding

Comments

[boriskogan]

Does this have to do with mitochondrial DNA?

[shkrobius]

Nope

[boriskogan]

But can't they use mitochondrial DNA analysis to determine if the animals back then are ancestors of today's animals?

[shkrobius]

They can, but the problem is to find these animals who are the direct ancestors of today's animals that lived 500 Mya. You would find all kinds of strange creatures, but guessing which one of the lineages will have direct ancestors 500 Mya would be a very difficult task. Also, if the DNA is similar, this proves little. Who knows, may be pansmermists are right and Life has extraterrestrial origin. The planet X could be pollinated from the same source. They need 100% percent assurance that this is not the case; the planet is our Earth.

[boriskogan]

Does the answer have to do with a massive extinction event?

[shkrobius]

If that gives you the possibility of a decisive test, why not? However, I do not see how. Ok, here is a hint: if it is Earth, then their future is our present. If it isn't...

[boriskogan]

You could leave an object with predictable chemical changes in a fixed location, then communicate with the present and have them check to see if it's there.

[boriskogan]

A block of uranium 235, for instance.

[shkrobius]

The problem with planting the object is inability to locate it in the future. There is geological activity, continental drift and subduction, etc. You are thinking in the right direction, though.

[boriskogan]

I'm not smart enough on physics to know whether you could have a non-degrading earth orbit over 500 MY. I guess you could launch a bunch of the blocks into it-hopefully at least one would survive collisions with space crap well enough to be detected in the future.

I have no idea how you'd guarantee the survival of your modified dinoflagellate line over 500 million years, let alone that their descendants in the future would be the ones that were selected for the time travel, instead of some random other dinoflagellate. Also, wouldn't it appear to the biologist that the dinoflagellates he had brought with him to the past have ALWAYS had the inserted random DNA sequences in them? Is it not likely that the sequences would mutate over 500 MY through transcription errors in such a way as to be unrecognizable?

[arbat]

My first thought was - plant something that they will be able to discover in themselves.

[shkrobius]

Right thinking. But it does not have to be themselves. They can take anything they like with them.

[boriskogan]

Also, what about finding a niche lifeform whose niche would have been unchanged 500 Mya? Halofiles (isn't that's what the salt-loving microbes are called?) or something? Then you could compare DNA for ancestry.

[shkrobius]

Well, we do not know what was the DNA of bacteria living 500 Mya, we only speculate that it was similar to today's bugs. On top of that, bacteria swap their genes. Furthermore, one can make the same argument that such bacteria came from another planet, including the Earth. The planet X may not be Earth even if you find exactly the same purple bacterium.