1) The Earth formed around 4.5 billion years ago from a disk of dust and gas surrounding the young Sun. Over millions of years, the planet developed a layered core and crust as heavier elements sank to the center. 2) Early microbes evolved and began producing oxygen through photosynthesis, transforming the atmosphere. The rise of oxygen allowed more complex life like fish and eventually amphibians, dinosaurs, and primates to emerge. 3) The first humans evolved around 2 million years ago, living as hunter-gatherers. Control of fire was a major development that allowed expansion of human activity. Settlement and agriculture began around 10,000 years ago, leading to growth of early civilizations along rivers.