Which of the following was most likely to have been absent in free form in the primordial atmosphere at the time of the origin of life?

The primitive environment was reducing because in it

Assertion: The earliest organisms that appeared on the earth were non-green and presumably anaerobes.
Reason: The first autotrophic organisms were the chemoautotrophs that never released oxygen.

Which compound has a very important role in prebiotic evolution?

The atmosphere became oxidising with the appearance of

Read the following statements and find out the correct ones:
$A.$ Spontaneous generation theory was approved once and for all.
$B.$ Pasteur showed that in pre-sterilized flasks,life did not come from killed yeast.
$C.$ Oparin observed the formation of amino acids by creating electric discharge in a closed flask.
$D.$ Life appeared $500$ million years before the formation of the earth.