Why are fossils rarely found in Precambrian layers

How does friction with the atmosphere affect the speed of an artificial satellite

What causes darkening of the skin as melanin production increases

An ecologist studied the same species of deer during the summer and the winter. she noticed that during the summer, when there was plenty of food, the deer were energetic and playful. however, during winter when food was scarce, the deer moved more slowly and did not run unless they needed to escape a predator. which scientific fact is best supported by her observations?