Which era spans from 4.5 billion to 542 million years ago?

The correct answer is Precambrian because this era encompasses the vast majority of Earth's history, beginning around 4.5 billion years ago with the formation of the Earth itself, and lasting until approximately 542 million years ago, just before the Cambrian period. The Precambrian is critical as it covers the time during which the Earth cooled, the first continental masses formed, and the earliest life forms, mainly simple, unicellular organisms, developed.

During this extensive time span, significant geological and biological changes occurred, setting the stage for more complex life forms that emerged in the subsequent Paleozoic Era. This era is notable because it accounts for about 88% of Earth's geological time, highlighting its importance in the development of the planet's crust and early biosphere.

The other eras, such as Paleozoic, Mesozoic, and Cenozoic, are each characterized by distinct biological and geological developments but occur after the Precambrian. The Paleozoic Era follows the Precambrian and starts at 542 million years ago, marking the advent of more complex life forms. Thus, the Precambrian stands uniquely as the foundational era of Earth's history.