Earth's history spans approximately 4.5 billion years, beginning with the formation of the planet from dust and gas in the solar system. Over time, the surface cooled, allowing for the creation of oceans and the atmosphere. The earliest life forms, such as simple bacteria, emerged around 3.5 billion years ago, marking the start of biological evolution. Throughout its history, Earth has experienced significant events, including the Cambrian Explosion, which led to a rapid increase in biodiversity, and several mass extinctions, such as the one that wiped out the dinosaurs 66 million years ago. These events shaped the planet's ecosystems and paved the way for the rise of mammals and eventually humans.