What is the correct order in which the following appeared during the early evolution of life on Earth?
a. Oxygen, ozone, photosynthesis, life on land
b. Photosynthesis, oxygen, ozone, life on land
c. Life on land, photosynthesis, oxygen, ozone
d. Ozone, oxygen, photosynthesis, life on land
e. Oxygen, photosynthesis, life on land, ozone
Answer: b. Photosynthesis, oxygen, ozone, life on land.