Problem 4
Describe two ways in which the sudden appearance of oxygen in the atmosphere about 2.5 billion years ago influenced the development of modern life-forms.
Problem 6
(6) Currently, oceans cover about 71 percent of Earth's surface. This percentage was much higher early in Earth's history. Explain.
Problem 8
Suggest at least one reason plants moved onto land before large animals.
Problem 9
Some scientists have proposed that the environments around black smokers may be similar to the extreme conditions that existed early in Earth history. Therefore, these scientists look to the unusual life that exists around black smokers for clues about how the earliest life may have survived. Compare and contrast the environment of a black smoker to the environment on Earth approximately 3 to 4 billion years ago. Do you think there are parallels between the two? If so, do you think black smokers are good examples of the environment that earliest life may have experienced? Explain.
Problem 11
Suggest a geologic reason why the rift valley system of East Africa is so rich in human ancestor fossils.
