Cambrian period, ~525mya. Gondwana (southern continent) beginning to form.

Permian period, ~275mya. Continents collide, forming Pangaea Permian period, ~275mya. Continents collide, forming Pangaea. Lava flows, ash cools the atmosphere, huge glaciers, sea level drops, oceans turn over, toxic gases released. Result: Mass extinction.

Cretaceous period, ~140mya Cretaceous period, ~140mya. Pangaea separates into southern (Gondwana) and northern (Laurasia) continents.

Dominant life forms of the past: some very broad generalizations Precambrian: prokaryotes Cambrian-Ordovician: marine invertebrates, algae Silurian-Devonian: fish diversify, and remain the dominant group in the seas; land colonized Carboniferous-Permian: amphibians, insects, forests of ferns and seedless vascular plants. Mesozoic era: reptiles (inc. dinosaurs), gymnosperms Cenozoic era: mammals, flowering plants, new insects

BUT… These are dangerously broad generalizations, and only a starting point. Most groups originated long before they became dominant. (e.g. 1st reptiles in Carboniferous, 1st mammals in Triassic)