This graph best represents the populations of marine groups before and after the
a. cambrian explosion
b. ordovician extinction
c. permo-triassic extinction event
d. alleghenian orogeny

Which of the layers of the earth has the following three characteristics? i. it is made of molten rock. ii. it has currents that are constantly moving. iii. earth’s plates float on top of its currents.

The creation of the european union has had all of the following effects except

What is the term for a government where power is carefully divided between a central government and several regional or provincial governments? a.) unified or central government b.) federal government c.) confederate government d.) republican government