Why do scientists think the first living cells to appear on earth were probably anaerobic heterophs?

Answer 1

Scientist knew that the earth lacked oxygen so they predicted that these organisms were anaerobic. They most likely used the abundant organic molecules in the ocean for food. Heterotrophy obtain there food rather then making it.

Answer 2

Thats a long question, basically there is some fossil evidence that shows cells without characteristic structures that are use for photosynthesis (see cyanobacteria), this coupled with the fact that photosynthesis appears to be a more advanced feature (more complex) not present in all early life. The original organism must have been simple by comparison. It is much more probable that the progenitor of all life lacked these features rather than most every other heterotropic bacteria later to evolve all spontaneously discarding the art of photosynthesis. This would make the first cell a heterotroph not an autotroph.

If you look at geology, life evolved before the iron in the sea got oxidized and fell out of solution as rust making many of the iron or deposits of today. Simply put, if iron could not rust, there was no oxygen in the early atmosphere. Not untill the ancestors of modern cyanobacteria had filled the atmosphere with oxygen did the iron fall out of solution in sea water. So this very early life that would one day become cyanobacteria, could not have needed oxygen to live so it must have been anaerobic.

Answer 3

There is a suggestion that undersea volcanic fissures provided the nutrition, heat and stability necessary for the cells to survive. Also, they may have been sulphur based, rather than oxygen, because of its reactivity and prevalence in these thermal areas.