The reason why nost scientists thought that the first true cells formed on Earth were anaerobic is being shown in the second option :B. because there was no oxygen on early Earth. Paying attention to this fact scientists discovered that first cells were prokaryotes and greatest part of them created oxygen as a toxic by-product of their own metabolism which make them understand how the planet was provided with oxygen and made a conclusion that first cells were anaerobic.
D. The discoveries confirmed many but not all of the classifications that were based on observable traits, and scientists revised classifications when necessary.
The deccan traps in Jurassic times happened at the same time as the cretaceous mass extinction.
Oxygen if that is a answer choice
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