Which evolved first, photosynthesis or cellular respiration?

Because photosynthesis is a source of oxygen, it seems intuitive that photosynthesis evolved first: once enough O2 was in the air, then respiration would be able to arise in the newly oxygen-enriched atmosphere. However, some biologists have argued since the 1970's that respiration in fact evolved first.

i might be wrong but i think its a. let me know if i’m right and have a good rest of your day!

her next move would be to use agarose gel electrophoresis to separate the dna molecules of varying length and create a dna fingerprint.