Final answer:
Magma that reaches the Earth's surface is called lava, which rapidly forms fine-grained extrusive igneous rocks. In contrast, magma that cools slowly within the Earth forms coarse-grained intrusive igneous rocks.
Step-by-step explanation:
The magma that has reached the surface of the Earth is called lava.
Lava is molten rock that, once it reaches the Earth's surface, rapidly cools and solidifies to form extrusive, or volcanic, igneous rock. This type of igneous rock is typically fine-grained, as the rapid cooling process does not allow for large crystals to form. Contrastingly, if the magma cools slowly while still inside the Earth, it forms coarse-grained intrusive igneous rocks such as granite.
Earth's geology is significantly influenced by plate tectonics, which governs various geological phenomena including volcanic eruptions that bring magma to the surface as lava. Igneous rocks, whether extrusive or intrusive, are part of the rock cycle where they can be transformed into sedimentary rocks or metamorphosed into metamorphic rocks over geological time due to the movement of tectonic plates and changing environmental conditions.