How do scientists know about what life was like before humans appeared?

Which one of these is a involving in both sexual and asexual reproduction

How do tides affect the organisms living in intertidal zones? a. no organisms live in intertidal zones due to the tumultuous environment. b. the mechanical forces of the waves keeps the organisms clean. c. only plants live in intertidal zones because the animals float away with the waves and never return. d. the mechanical forces of the waves can dislodge the organisms from their habitat.

The circles, or orbits, for electrons are called energy levels. each level can hold only a certain number of electrons. add electrons to each level until you can't add any more. how many electrons can each level hold?