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

3. 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.

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

6. 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

7. 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)