History of earth By who Period: 4600 BCE to 4500 BCE Planetary Accreation Period: 4500 BCE to 4500 BCE Formation of Earth Period: 4000 BCE to 4000 BCE End of the Late Heavy Bombardment Period: 2300 BCE to 2300 BCE Atmosphere becomes oxygen-rich Period: 2 BCE to 2 BCE First Hominies Appeared Period: 230 to 66 Dinosaurs Roam Earth Period: 380 to 380 First Vertebrate of animal Period: 530 to 530 First Cambrian Explosion Period: 4527 to 4527 Formation of the Moon