Question

Scientists believe that early plants released oxygen in a process called photosynthesis. where did the carbon dioxide needed for photosynthesis come from in the early atmosphere?

Answer 1

Animals produce carbon dioxide used by plant for photosynthesis

Answer 2

The answer on USA test prep is D. Early bacteria and plants released carbon dioxide as well as oxygen when they performed photosynthesis. because bacteria could have been aerobic back then and released carbon dioxide for the plants to use in photosynthesis.