The answer to your question is Aksum
Answer:
They have small crystals.
Explanation:
Extrusive igneous rocks form when lava reaches the Earth's surface a volcano and cools quickly. Most extrusive or volcanic rocks have small crystals. Examples include basalt, rhyolite, andesite, and obsidian. Intrusive, or plutonic, igneous rocks form when magma cools slowly below the Earth's surface.
Each era is subdivided into a number of periods. The periods of the Cenozoic, the present era, are further divided into epochs. Many divisions of the geologic time scale are based on events in Earth's geologic history. Some divisions are based entirely on the fossil record.