In which era did the first life forms appear?

The first life forms appeared during the Archeozoic Era, also known as the Archean. This period, which began around 4 billion years ago and lasted until about 2.5 billion years ago, is marked by the emergence of the earliest known life, primarily simple single-celled organisms like prokaryotes (bacteria). Fossil evidence, such as stromatolites, which are layered structures created by the activity of these microorganisms, supports the existence of life during this time.

The subsequent eras, including the Proterozoic, Paleozoic, and Mesozoic, show more complex life forms evolving. The Proterozoic Era saw the development of multicellular organisms, while the Paleozoic Era is recognized for the explosion of diverse marine life forms and the colonization of land by plants and animals. The Mesozoic Era, often called the Age of Reptiles, is well-known for the dominance of dinosaurs. Thus, the Archeozoic is foundational to the history of life on Earth, establishing the very first organisms that paved the way for more complex life forms in later eras.