The term 'geological era' refers to a period of time in Earth's history, divided into three main eras: the AEON (4 letters), Mesozoic (8 letters), and Silurian (8 letters). The AEON is the longest of the three eras, spanning from 4.6 billion years ago to the present day. The Mesozoic Era is the middle era, lasting from 252 million to 66 million years ago, and is known as the 'Age of Reptiles'. Finally, the Silurian Era is the shortest of the three, lasting from 443 million to 416 million years ago, and is known for its abundance of marine life.