12283"Life May have Originated Billions of Years Before the Earth was Created"
- May 18, 2014URL to an interesting post from The daily Galaxy blogLife originating billions of years before Earth was formed is a staple of science fiction. The idea leads to the question of what advanced life might be like in a billion or so years. Extinct? Evolved into something we'd be unable to recognize? Migrated to another astral plane?Chris
Did you ever stop to think, and forget to start again?
Why haven't we discovered signs of life beyond Earth? As Carl Sagan said, the absence of evidence is not evidence of absence. This thought is well known in other fields of research. Astrophysicists, for example, spent decades studying and searching for black holes before accumulating today’s compelling evidence that they exist. The same can be said for the search for room-temperature superconductors, proton decay, violations of special relativity, or for that matter the Higgs boson. Much of the most important and exciting research in astronomy and physics is concerned exactly with the study of objects or phenomena whose existence has not been demonstrated.The search for life should not and cannot be limited to the search for Earth-like features. This cosmic view of the diverse nature of extraterrestrial life, is a revolutionary perspective which has the potential to make a great impact on our way of thinking as profound as the Copernican revolution.
We should be careful if we ever happen upon extraterrestrial life, Hawking warns. Alien life may not have DNA like ours: "Watch out if you would meet an alien. You could be infected with a disease with which you have no resistance."
Recently, scientists are content to define life using the "chemical Darwinian definition" that involves "self-sustaining chemical systems that undergo evolution at the molecular level."
There are in fact a number of genetic-studies which purport to demonstrate that the common ancestors for Earthly life forms may have first began to form billions of year before the Earth was created. It has been speculated the first steps toward actual life may have begun with self-replicating riboorganisms whose descendants fell to Earth and other planets through mechanisms of panspermia, triggering the RNA world and then life as we know it. Life on some planets may be like life on Earth. Life on other worlds may have a completely different chemistry, and may not even possess a genetic code.
Life that may have been originated elsewhere, even within our own solar system, could be unrecognizable compared with life here and thus could not be detectable by telescopes and spacecraft landers designed to detect terrestrial biomolecules or their products. Life might be based on molecular structures substantially different from those on Earth.
What we normally think of as 'life' is based on chains of carbon atoms, with a few other atoms, such as nitrogen or phosphorous, Hawking observed in his lecture, Life in the Universe. We can imagine that one might have life with some other chemical basis, such as silicon, "but carbon seems the most favorable case, because it has the richest chemistry."
Organic molecules are now known to be common throughout the universe. Life, then, is assumed to be carbon-based.The Earth was formed largely out of the heavier elements, including carbon and oxygen. Somehow, Hawking observes, "some of these atoms came to be arranged in the form of molecules of DNA. One possibility is that the formation of something like DNA, which could reproduce itself, is extremely unlikely. However, in a universe with a very large, or infinite, number of stars, one would expect it to occur in a few stellar systems, but they would be very widely separated."