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

[vdinets]

The genetic code is pretty much the same for all eucaryotes, and it's extremely unlikely to be the same on other planets.
Also, the composition of the Solar system is unique, and the Moon had already had most of its craters by 500 myrs.

[shkrobius]

We do not know that. For all we know, the eukaryotes may be from another planet; maybe even from our own Earth. The composition of the Solar system is not that unique, and other planets of the system also do not look exactly as expected. As for the dating of the craters on the Moon, it is just our guesswork. The expedition needs 100% certainty. They do not want to waste their resources on studying the planet that is not our Earth. The biologist claims he can provide such assurance. How?

[vdinets]

Hmm... but the procaryotes might also be from Earth, so any biological evidence would be meaningless. However, you can look at the sequence of magnetic field reversals and check for an identical sequence in Earth sediments of roughly the same time, the same way you use dendrochronology to date a piece of wood.

[shkrobius]

It has to be biological. The oldest fields you can map in detail date from 250 Mya. Rodinia is a mystery. Today's sediments will be in unusual places that cannot be located with certainty. Also, it is hard to prove that the magnetization one presently detects in very old samples is not a younger overprint. I am afraid it would be inconclusive. It has to be some other idea.

[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.