Different World, Different Organisms?

This discussion suggests that much of the history of life on earth is due to a particular sequence of events that could have happened differently. It is tempting to ask what would have happened if key aspects of evolution on Earth had been different:

1. What if water weren't the solvent, and the common elements were not C, H, N, O, P and S? Could life (a self-replicating entity of any form) evolve?

2. What if life had evolved on land instead of in the ocean?

3. What if a different genetic code had appeared in the first self-replicators?

4. What if gravity were greater (or less)?

5. What if different materials were available for use by organisms?

6. What if there had been a different pattern or timing of mass extinctions?

Would life as we know it have evolved the same way? One would suspect that the trajectory of evolution would have been very different. Would Eukaryotes have even evolved?

It remains to be seen whether traces of life, present or past, will be found in other worlds. From this discussion, it seems likely that if signs of self-replication are found elsewhere, the forms of life may be very different than those seen on our planet. Our challenge may be not only to locate extraterrestrial life, but to recognize it.

Contributed by: Dr. Sara Via