Is the widely accepted scientific theory that characteristics of a population may change over time, and that current species may gradually give rise to new species.

Evolution theory

Explanation:

The evolution theory was developed by Darwin and it is a generally accepted theory that deals with gradual changes in the characteristics of organisms due to their quests to adapt to continuous changes in the environment.

As the environment of organisms keeps changing, the population of the organism keeps adjusting. Individuals that are able to adjust to the changes survive and are able to reproduce while the weak ones gradually die off from the population.

Hence, the entire characteristics of the population is changed with time as a result. The continuous changes sometimes lead to some species within the population giving rise to a new species entirely.

answer and explanation;

volcanic rocks are igneous rocks which form from lava, molten rock which has been thrust out of a volcano onto the surface of a rocky body such as an asteroid, planet, or dwarf planet.  

plutonic rocks are igneous rocks which form from subterranean chambers of molten rock or magma. plutonic rocks make up the base of continental crust as well as oceanic crust. their slow rate of formation causes them to be coarse grained since there is plenty of time for large crystals to form before the magma solidifies into rock.

the textural difference is that plutonic rocks are more coarse grained than volcanic rocks. plutonic rocks are coarse grained while volcanic are fine grained ; glassey or fragmental. since fine and coarse are adjectives the decision as to whether a rock is fine or coarse grained is generally made on the bases of whether or not the individual crystals can be seen in most if the rock.