Question

what was most likely responsible for the fact that organic molecules no longer form spontaneously on Earth?

Answer 1

Salutations! 1) A. The primitive earth had a lot of UV radiation. Photosyntesis originated O2 and O2 reacts generating O3 (ozone). The ozone layer prevents a lot of UV radiation to reach inorganic molecules and provide them with a lot of energy. Without that intense UV radiation, inorganic molecules cannot convert into organic molecules (because no other source of energy provides enough energy for that process). Hope this helps you!

Answer 2

Answer: Less ultraviolet light and more oxygen.

Explanation:

The early earth condition were different from now. There was more ultraviolet light as there was no ozone layer during the early earth conditions.

The oxygen levels at the time of early earth was also not high but after the evolution of cyanobacteria the level of oxygen rised very rapidly.

These conditions does not allow the formation of organic molecules from inorganic molecules.