Age of Earth and Geologic Time Scale PDF

# Age of Earth and the Geologic Time Scale ## Key concepts - **Age of the Earth**: The Earth has a very long history - 4.6 billion years of history. The age of the Earth is based from the radioactive isotopic dating of meteorites. The oldest dated rock from the Earth is only ~3.8 billion years old...

# Age of Earth and the Geologic Time Scale ## Key concepts - **Age of the Earth**: The Earth has a very long history - 4.6 billion years of history. The age of the Earth is based from the radioactive isotopic dating of meteorites. The oldest dated rock from the Earth is only ~3.8 billion years old. - **Rocks and Fossils**: - The history of the Earth is recorded in rocks but the rock record is inherently incomplete. Some "events" do not leave a record or are not preserved. Some of the rock record may have also been lost through the recycling of rocks (recall the rock cycle). - Preserved in rocks are fossils or the remains and traces of plants and animals that have lived and died throughout the Earth's history. The fossil record provides scientists with one of the most compelling evidence for Charles Darwin's Theory of Evolution (increasing complexity of life through time). - **Rocks, Fossils and the Geologic Time Scale**: - The Geologic Time Scale - the timeline of the History of the Earth, is based on the rock record. - Geologic time is subdivided into hierarchal intervals, the largest being Eon, followed by Era, Period, and Epoch, respectively. Subdivision of Geologic time is based from significant events in the Earth’s History as interpreted from the rock record. - The mass extinction event which lead to the extinction of the dinosaurs occurred around 66.4 million years ago marks the boundary between the and Mesozoic Era (Age of the Reptiles) the Cenozoic Era (Age of Mammals). This mass extinction event may have been pivotal in the rise in dominance of the mammals during the Cenozoic Era. ## Geologic Time Scale | EON | ERA | PERIOD | MILLIONS OF YEARS AGO | MAJOR BIOLOGICAL EVENTS | |:------|:---------|:-----------------|:-----------------------|:------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | | | Quaternary | 1.6 | Rise of civilization and agriculture. Extinction of large mammals in northern hemisphere. | | | Cenozoic | Pleistocene | 1.8 | Modern humans appear. Four major glaciations cause rapid shifts in ecological communities. | | | | Pliocene | 5 | Extensive radiation of flowering plants and mammals. First hominids appear. | | | | Miocene | 23 | Coevolution of insects and flowering plants. Dogs and bears appear. | | | | Oligocene | 38 | Worldwide tropical rainforests. Pigs, cats, and rhinos appear. Dominence of snails and bivalves in the oceans. | | | | Eocene | 54 | Early mammals abundant. Rodents, primitive whales and grasses appear. | | | | Paleocene | 65 | Early placental mammals appear; first primates; modern <br>birds. | | | Mesozoic | Cretaceous | 146 | Marsupials, ants, bees, butterflies, flowering plants appear. Mass extinction of most large animals and many plants. | | | | Jurassic | 208 | Dinosaurs and gymnosperms dominate the land; feathered dinosaurs and birds appear. Radiation of marine reptiles. | | | | Triassic | 245 | Origin of mammals, dinosaurs and true flies. Less diverse marine fauna. | | | Paleozoic | Permian | 286 | Gymnosperms, amphibians dominant. Beetles, stoneflies appear. Major extinction of 95% of marine species and 50% of all animal families. | | | | Pennsylvanian | 325 | First reptiles, cockroaches and mayflies appear. Extensive coal swamp forests. Sponge reefs. | | | | Mississippian | 360 | Echinoderms, bryozoans dominant in oceans. Early winged insects. First coal swamp forests. | | | | Devonian | 410 | First amphibians. Extensive radiation of fish, land plants. Many corals, brachiopods and echinoderms. | | | | Silurian | 440 | First spiders, scorpions, centipedes, early insects, vascular plants, jawed fish and large reefs appear. | | | | Ordovician | 505 | First land plants, primitive fungi, sea weed appear. Diverse marine life: corals, molluscs, bivalves, echinoderms, etc. | | | | Cambrian | 543 | Rise of all major animal groups. Metazoan life abundant; trilobites dominant. First fish. No known terrestrial life. | | Proterozoic | | | 570 | Origin of multicelled organisms. First sponges, colonial algae and soft-bodied invertebrates. | | Archean | | | 2,500 | Oxygen levels rise as a result of photosynthetic organisms. First eukaryotes (single-celled algae): 1.4 billion years old. Earliest life, anaerobic prokaryotes (bacteria, archaeans) originate 3.5 billion years ago. | | Hadean | | | 3,800-4,600 | No life known. Cooling and solidifying of Earth’s crust. | ## Fossils - Fossils are essential in the subdivision of the geologic time. - **Biostratigraphy** is a sub-discipline of stratigraphy, which deals with the use of fossils in the correlation and establishments of the relative ages of rocks. ## Relative Dating - Dating of events or substances in comparison with one another, in chronological order. ## Absolute Dating - An estimate of the true age of a mineral or rock or fossil based on the rate of decay of radioactive materials. ## Image Descriptions - **Figure 1**: Evolution of life through Earth's history, a schematic diagram highlighting the different geological periods throughout the Earth's history. - **Figure 2**: A table showing the geologic time scale; it includes Eon, Era, Period, and Millions of years ago for each period. - **Figure 3**: An illustration showing how the deeper a rock layer is the farther back in time the rock strata exists. - **Figure 4**: A table showing the difference between relative dating and absolute dating. - **Figure 5**: A diagram showing the major events for different Eon periods for the Earth's formation.