Sarah Moralez: Geologic Timeline

Cambrain Period 570-500 MYA

570 BCE

Trilobites left a huge number of fossils. They had flattened, segmented, plated bodies that helped to protect them in seas that were filled with predators.

Ordovician Period 485 - 443 MYA

485 BCE

Ordovician seas were filled with invertebrates, dominated by brachiopods, bryozoans, trilobites, mollusks, echinoderms, and graptolites. The end of the Ordovician was heralded by a mass extinction, the second largest in Earth history.

Silurian Period 443 - 416 MYA

443 BCE

Silurian fossils show extensive coral reefs. The climate was generally warm and stable, in contrast to the glaciers of the late Ordovician and the extreme heat of the Devonian. Lichens were probably the first photosynthetic organisms to cling to the rocky coasts of the early continents.

Devonian Period 416 - 358 MYA

416 BCE

Known as the “Age of Fishes". The supercontinent Gondwana occupied most of the Southern Hemisphere. Reef ecosystems contained numerous brachiopods, still many trilobites, tabulate and horn corals. Placoderms underwent wide diversification and became the dominant marine predators. Lycophytes, horsetails and ferns grew to large sizes and formed Earth’s first forests. Rhyniella praecusor, was a flightless hexapod with antennae and a segmented body. 2nd of mass extinction

Carboniferous Period 359 - 299 MYA

359 BCE

Carboniferous coal was produced by bark-bearing trees that grew in lowland swamp forests. Vegetation included giant club mosses, tree ferns, great horsetails, and tall trees with strap-shaped leaves. Growth of these forests removed huge amounts of carbon dioxide from the atmosphere, leading to a surplus of oxygen. Amphibians were also growing in size and diversity. There were predatory species that resembled modern-day crocodiles.

Permian Period 299 - 251 MYA

299 BCE

Reefs were large and diverse ecosystems with sponge and coral species. Ammonites, were common, and brachiopods. The lobe-finned and spiny fishes were being replaced by sharks and rays. Giant swamp forests of the Carboniferous began to dry out. The mossy plants that depended on spores for reproduction were being replaced by the first seed-bearing plants, the gymnosperms. Gymnosperms are vascular plants, able to transport water internally. The two types are animals were Synapsids and Sauropsids

Triassic Period 251-199 MYA

251 BCE

Fossils of early ichthyosaurs are lizard-like and clearly show their tetrapod ancestry. Plants and insects did not go through any extensive evolutionary advances during the Triassic. The Mesozoic Era is often known as the Age of Reptiles. The first mammals evolved near the end of the Triassic Period from the nearly extinct Therapsids.

Jurassic Period 199 - 145 MYA

199 BCE

Pangaea split apart. living things had evolved the capability of living on the land rather than being confined to the oceans. Dinosaurs may have been the dominant land animals, but they were not alone. Early mammals were mostly very small herbivores or insectivores and were not in competition with the larger reptiles. The largest marine carnivores were the Plesiosaurs.

Cretaceous Period 145 - 66 MYA

145 BCE

The Cretaceous Period was the last and longest segment of the Mesozoic Era. Sections of the supercontinent Pangaea were drifting apart.

Tertiary Period 66 - 2.6 MYA

66 BCE

Climatic, oceanographic, and biological change. It spanned the transition from a globally warm world with high sea levels and dominated by reptiles to a world of polar glaciation, sharply differentiated climate zones. The Tertiary witnessed the dramatic evolutionary expansion of not only mammals but also plants, insects, birds, corals, deep-sea organisms, marine plankton, and mollusks, among many other groups.

Quaternary Period 2.6 MYA - Present day

2 BCE

Glaciers covered approximately 30 percent of Earth’s surface. Enormous herbivores such as mammoth, mastodon, giant bison and woolly rhinoceros, which were well adapted to the cold. Humans arrived.