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

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.
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.