Geologic Time Scale: a timeline of Earth’s history divided into eons, eras and periods.
o Precambrian (4600-542 mya): Anaerobic forms evolved followed by photosynthetic life, aerobic forms and eukaryotes. Life existed only in the sea.
At the end of the Precambrian Time: There was a mass extinction of single-celled life.
o Paleozoic Era (542-251 mya):
a. The Cambrian Period: Development of marine life such as trilobites, jellyfish, sponges and worms.
b. Ordovician and Silurian Periods: Ancestral Octopi and Squid, aquatic arthropods, jawless fish, first land plants evolve (moss).
c. Devonian Period: Ferns adapted to drier areas, insects appear on land, bony fish, and first amphibians evolved from leg-like finned fish.
d. Carboniferous and Permian Periods: Reptiles evolve from amphibians, winged insects evolve such as dragonflies and cockroaches, and plants formed in swampy forests.
At the end of the Paleozoic: There was a mass extinction of plants and animals.
50% of land organisms and 95% of marine organisms went extinct.
o Mesozoic Era (251-65.5 mya):
a. Triassic Period: Increasing dominance of dinosaurs, mammals first appeared, and Coelophysis (a meat eating, light hollow boned dinosaur) ran on hind legs.
b. Jurassic Period: Dinosaurs dominant land animal. First bird (Archaeopteryx) appeared.
c. Cretaceous Period: Dinosaurs such as T-Rex still dominate, crocodiles and sea turtles present in the water.
At the end of the Mesozoic: There was another mass extinction where more than half of all plants and animals groups were wiped out, including all the dinosaurs.
o Cenozoic Era
a. Paleogene Period: Marine mammals such as whales and dolphins evolve, flowering plants and insects flourish on land, grasses evolved, providing a food source that encouraged the evolution of grazing mammals.
b. Neogene Period: Many mountain ranges were formed and ice started to develop in the Arctic. Climates continued a cooling and drying trend.
c. Quaternary Period: Time of the ICE AGE! OHHHH BURRRR! In oceans, algae, coral, mollusks, fishes, and mammals thrive; on land, mammals such as bats, dogs, cats, cattle, and mammoths were common, and about 6-7 million years ago an adaptive radiation began that lead to the ancestors of our own species Homo sapien.