Question

most of the molecular oxygen in the early atmosphere of earth resulted from decaying primitive plants and animals volcanic eruptions lightning striking earth photosynthesis in primitive plants

Explanation:

• Decaying primitive plants and animals would consume oxygen rather than produce it.
• Volcanic eruptions release gases like carbon dioxide, sulfur dioxide, etc., not molecular oxygen in large amounts relevant to early - atmosphere oxygen buildup.
• Lightning striking Earth can cause some chemical reactions, but it is not the main source of molecular oxygen in the early atmosphere.
• Photosynthesis in primitive plants (such as cyanobacteria which are photosynthetic prokaryotes) is the process that converts carbon dioxide and water into organic compounds and releases oxygen as a by - product. This was the major source of molecular oxygen in the early Earth's atmosphere.

Answer:

photosynthesis in primitive plants