When did the phanerozoic eon begin

541 million years ago

Explanation:

The Phanerozoic Eon is the most recent eon. It started 541 million years ago, and it still lasts, thus we are living in this eon as well. The Phanerozoic Eon has seen lot of changes, from explosion of the life, to big catastrophic events, big changes in climate, changes in the continents and oceans, and most recently the appearance of the most intelligent species, the humans. Through this period the Earth has been dominated by fish, sinapsids, dinosaurs, mammals, all having their fair share of dominance on the planet. The continents have been constantly on the move, creating supercontinents on multiple occasions, but then falling apart and creating numerous small ones. There has been multiple mass extinctions as well, some caused by intense volcanic activity, some by meteorite impacts.

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.