Q. 1. Modern theory suggests that an early (pre-life) atmosphere on Earth was a reducing one. Why (for what reasons) is it believed that oxygen was not present while life formed on Earth?

2. What proposed energy sources existed on this early (pre-life) Earth?

3. In 1950s, Stanley Miller performed a set of experiments to determine whether life might have evolved given the conditions stated in the answers to questions 1 and 2.

a. How was the experiment designed?

b. What were the essential controls?

c. What was produced in the experiment?

d. What did results imply about the possible origin of life on Earth?

e. There is a general agreement that life should have evolved in the oceans originally and only much later invaded land. What factors of the physical environment on the early and evolving Earth support these ideas? Changes in which of these factors were essential for life to survive on earth?

f. Most of us can’t even make up a world without oxygen. Though, as you learned earlier, chemically oxygen is a powerful oxidizing compound. What effect(s) would the enhance in oxygen levels of the atmosphere have on the organisms that existed at that time?