The mass extinction that led to the loss of 96% of marine life and 70% of terrestrial life was most likely due to a supernova, an asteroid impact or .

What are four key elements of the study of economics?

List two limitations of natural selection

In addition to seeds, which of the following characteristics are unique to the seed-producing plants? a) sporopollenin b) lignin present in cell walls c) pollen d) use of air currents as a dispersal agent e) megaphylls