The boundaries of eras are marked by great worldwide changes in?
a) earth’s crust
b) life forms
c) climate
d) continental coastline

Which of the following terms describes the layers of air surrounding the earth ?

Which descriptions refer to cirrus clouds? check all that apply. are fluffy are wispy produce snow form at high altitudes form from ice crystals

Permafrost occurs in the tundra and tundra-forest biomes of eastern europe