Answer: free oxygen.
- A methane gas
- B ammonia gas
- C free oxygen
- D water vapour
Correct answer: C. free oxygen
Explanation: The early reducing atmosphere contained methane, ammonia and water vapour but essentially no free oxygen.
A simple phylogenetic tree: a common ancestor branches into several descendant lineages over time, with each branch point marking a speciation event.
Concept context
Origin of life, Darwin's theory, natural selection, speciation, and evidence for evolution.