When life first apeared, the atmosphere has no oxygen. thus, you can expect the first living forms were:
a. photosynthetic, using light to produce oxygen
b. aerobic, using oxygen to obrain energy
c. anaerobic, using inorganic substances for energy and food
d. heterotrophic, using organic substances for food

The correct answer is option D.

Explanation:

These organisms were called heterotrophic anaerobic organisms. Because there was no oxygen in the atmosphere at that time, these organisms did not breathe oxygen so its necessarily they were anaerobic.

These organisms probably consumed naturally found amino acids. After digesting amino acids, early bacteria produced carbon dioxide and methane as waste products.

Thus, the correct answer is option D.

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