Because magma cools very quickly when it erupts onto the earth's surface the crystals in the rock don't have much time to grow and this often results in
these 2 characteristics of extrusive igneous rocks

explanation:

on disadvantage of hydroelectric power is the cost. another disadvantage of using hydroelectric power is finding a water source powerful enough to harvest hydroelectric power.

in 1859, charles darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. he defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".