Earth's first atmosphere was composed of
A) oxygen, hydrogen, and helium.
B) hydrogen and helium, with trace amounts of ammonia and methane.
C) gases from volcanic eruptions.
D) oxygen, water vapor, carbon dioxide, and methane.
Question 2
Earth's original atmosphere was
A) very similar to the atmosphere we have today.
B) rich in both O2 and O3.
C) obliterated after the birth of the Sun.
D) a mixture of N2, CO2, and O3.