Question

5. The atmosphere of early Earth is unlike today's atmosphere.

A. When did oxygen first appear in Earth's early atmosphere? (3 points)
B. What factor caused the appearance of oxygen? (3 points)
C. What is one form of evidence used to support this theory? (4 points)

Answer 1

A. Oxygen first appeared in Earth's early atmosphere about 2.4 billion years ago.

B. The appearance of oxygen was caused by the emergence of photosynthetic organisms, such as cyanobacteria, which began to produce oxygen as a byproduct of photosynthesis.

C. One form of evidence used to support this theory is the presence of banded iron formations in sedimentary rocks. These formations contain layers of iron oxide that were likely deposited as a result of the reaction of iron dissolved in seawater with the oxygen produced by photosynthetic organisms. The presence of these formations suggests that oxygen was not present in Earth's atmosphere before the emergence of photosynthetic organisms.

Step-by-step explanation: