Problem 3
What does the existence of iron-rich rocks during the Precambrian indicate about the evolution of Earth's atmosphere?
Problem 4
What are two ways that the appearance of a significant amount of oxygen in the atmosphere relates to life?
Problem 7
Contrast the eastern and western margins of North America during the Cenozoic era in terms of their relationships to plate boundaries.
Problem 8
Why do you think plants moved onto land before animals?
