Was oxygen a part of Earth's early atmosphere? Explain how today's atmosphere evolved to support life

Question

What will be an ideal response?

Answer 1

No, it is hypothesized that Earth's early atmosphere contained methane, hydrogen, ammonia and some water vapor. Oxygen came later, and in fact, there is oxygen in today's atmosphere because of life. Stromatolites and other photosynthetic organisms would have begun adding oxygen, a product of photosynthesis, to Earth's early atmosphere. Oxygen tends to disappear from the atmosphere almost as soon as it is released because it readily combines with iron in the soil and ocean water. Geological evidence indicates that Earth's surface iron became saturated with oxygen about 2 to 2.5 billion years ago, after which the proportion of oxygen in the atmosphere began steadily increasing. Oxygen metabolism produces much more energy per mass of food than other reactions, and biologists speculate that this greater efficiency allowed for the development of multicelled organisms at about that same time. Also, an oxygen abundance of only 0.1 percent would have created an ozone screen, protecting organisms from the Sun's ultraviolet radiation and later allowing life to colonize the land.