Has it been proven that all life on Earth evolved from a UCA or is it still possible that life emerged more. .

Question

Than once? I'm of the opinion that if the conditions that allowed for life to begin existed on earth, then there's no reason to deny the possibility that life could have begun on more than one occasion. Has that notion been ruled out or is it still open for speculation?

Answer 1

Life could indeed have emerged many times, perhaps surviving for millions of years, and then and died out, before UCA took hold.   It's even possible that many different forms of life were existing simultaneously at various stages of early evolution, in many different parts of the world, but once UCA gained a foothold, and spread throughout the world, it found all other life forms to be nothing but a nice source of nutrients, and wiped all traces of these life forms out.   It is even possible that other life forms started *after* UCA, but did not last long before being eaten.

There is nothing in the theory of evolution that depends on life all being traceable to a single universal common ancestor (UCA) ... e.g. there is nothing contradictory about the concept that, say, plants and animals started from different ancestors ... but all the evidence is that all life forms share a common ancestor.

Answer 2

The evidence supports that all known life descended from one common ancestor.  This is not inconsistent with life emerging more than once.  Life could have emerged a number of times and fizzled before the "UCA" appeared.  There could have been life in several isolated regions when "near life" conditions were worldwide, but every tested organism shows evidence of common descent..  There are no known organisms detected by visible growth (including molds and bacterial colonies) that lack the features.  Molecular tests would not pick up organisms from another line since they are based on the common features of life such as the universal genetic code.

Answer 3

Well in purely scientific terms, nothing can be ruled out until another solution is proven, so until the actual origin of life is discovered other theories can't be disproven. Although the abiogenesis theory is the most widely accepted in the scientific community, others, including panspermia  have been proposed.

However, the fact that all life on earth, including viruses, reproduces using DNA components speaks volumes for the veracity of a singular origin of life. Though, it is always possible that there were multiple origins of life and that DNA-using organisms ultimately were the most successful and dominated the other species. If that were true, however, it would have occurred early in life's history or there would be some record of other forms of life.

Answer 4

The concept of a single common ancestor breaks down when you take into account horizontal gene transfer.  It is better to view the UCA as a population rather than an individual.

There are some fringe theories of multiple beginnings of the three domains, Eukarya, Archaea, and Bacteria, but the overwhelming consensus is there was one original population that diverged into three main groups.