Photosynthesis must have preceded respiration on the earth. Why?

Answer 1

ANIMALS require respiration and (except for animals living around volcanic undersea vents) animals are ultimately parasites on the plants.

So plants, living thru photosynthesis, must have preceded breathing animals. There's nothing to eat unless plants are already there first. (This remains true even in a primitive world composed of one-celled plants and one-celled animals).

Answer 2

The layer of gas surrounding our planet (the original atmosphere) was composed entirely of gases released from volcanos. Oxygen was not a part of this mix due to its chemistry (i.e. it tends to react with - oxidize - other compounds and/or elements). It was present in the primordial atmosphere mainly as water and CO2, and a few other gases. Eventually, the processes of photosynthesis released enough oxygen to sustain other form of life, in particular those relying on respiration.

Answer 3

Nope - the idea here is that there was no free oxygen to
respire prior to photosynthesis making it.

However, that's simply not true. There was considerably
LESS oxygen, but that's a far different case than none.

Photosynthesis is no an absolute requirement for
respiration - but it surely helps if there is little O2
available.

Answer 4

because there was almost no free oxygen in the atmosphere around the time Photosynthesis was developed in small microorganisms

Answer 5

need oxygen for respiration (oxidative), phorosynthesis produces oxygen as a by product, and needs no oxygen to drive the reaction.

Answer 6

i dnt no