How did early earth's atmosphere differ from Earth's atmosphere today?

Answer:
The early Earth had a reducing atmosphere, made up predominantly of methane, ammonia, and water vapor. All of these (except water vapor) are now present in trace quantities only; the atmosphere is now predominantly nitrogen and oxygen.
First answer by Ptorquemada. Last edit by Ptorquemada. Contributor trust: 551 [recommend contributor recommended]. Question popularity: 1 [recommend question].