Question: Why did civilization form when it did?
Answer: The Earth formed about 4.5 billion years ago. The first life forms appeared about 3.5 billion years ago. The first single-celled organisms were probably bacteria. The first multi-celled organisms were probably protists. The first animals were probably sponges. The first plants were probably green algae. The first land plants were probably mosses. The first animals to live on land were probably insects. The first vertebrates were probably fish. The first amphibians were probably amphibians. The first reptiles were probably reptiles. The first mammals were probably mammals. The first birds were probably birds. The first dinosaurs were probably dinosaurs. The first mammals to live on land were probably mammals. The first reptiles to live on land were probably reptiles. The first amphibians to live on land were probably amphibians. The first fish to live on land were probably fish. The first insects to live on land were probably insects. The first plants to live on land were probably plants. The first land animals were probably..