Chapter 8 explores the relationship between the geological Earth, its atmosphere, and the emergence of living things. The Earth and its atmosphere formed together about 4.5 billion years ago. Life forms emerged between 3.7 and 4.1 billion years ago, but biologically modern humans did not appear until between 150,000 and 100,000 years ago. These humans survived changing climate and weather patterns and about 12,000 years ago they figured out agriculture and started to live in permanent settlements.