Which best describe a secondary wave

Seed plants that lived during the carboniferous impact life on earth today because a. they are the ancestors of all plant life on earth. b. their remains formed coal, which is an important resource. c. they produced fossils that are used to date many geologic events. d. their presence caused oxygen levels to drop, allowing animals to evolve.

Hurry on the map above, arrow 1 points to a region where most people are

What is the thickest layer of earth called?