What is the geologic time scale?
The Geologic Time Scale is a record of major events and the diversity of life forms present in Earth's history. Geologists divide time (largest to smallest) into eons, eras, periods, and epochs based on the fossil record. Eons are the largest span of time and epochs are the shortest span of time that occur within a period, era, and epoch. The earliest and most vast span of time is the Precambrian eon, followed by the Paleozoic Era, Mesozoic Era, and Cenozoic Era. Today we are in the Cenozoic Era, Quaternary Period, and Holocene Epoch.
diversity of life
Each era has ended with a mass extinction where many organisms disappeared. Scientists use the Fossil Record to create a picture of the life forms present in each era.
paleozoic era
During the Paleozoic Era there was a tropical climate that created warm, shallow oceans. Many marine species could not adapt to this climate and disappeared. Different environments allowed for new life forms to develop on land.
Plants: Simple Mosses and Ferns, Cone Bearing and Seeded Plants
Animals: Early Invertebrates (Trilobites and Brachiopods), Early Vertebrate Fish, First Amphibians and Reptiles became dominant by the end of the Era
Plants: Simple Mosses and Ferns, Cone Bearing and Seeded Plants
Animals: Early Invertebrates (Trilobites and Brachiopods), Early Vertebrate Fish, First Amphibians and Reptiles became dominant by the end of the Era
mesozoic era
The Mesozoic Era is known as the "Age of the Dinosaurs". The climate continued to change as shifting plates created new landmasses. Volcanic activity occurred frequently due to the plates moving. Plants and animals that survived were more adapted to the changing conditions by having protective body coverings and being able to maintain a constant internal temperature. Plants also produced seeds that had protective coverings, allowing them to survive. The end of the Mesozoic era occurred around 65 million years ago when an asteroid or comet struck Earth.
Plants: Flowering plants with protective seed coverings
Animals: Reptiles were dominant (Dinosaurs), Small mammals and birds appeared, Mammals increased in variety
Plants: Flowering plants with protective seed coverings
Animals: Reptiles were dominant (Dinosaurs), Small mammals and birds appeared, Mammals increased in variety
cenozoic era
The Cenozoic Era is known as the "Age of Mammals" and is also the age of humans. The climate continued to change and became much cooler, causing several ice ages. Glaciers and ice sheets covered many areas of Earth and mountain ranges formed, changing the climate due to elevation. The Cenozoic Era also has the most diversity of life forms.
Plants: Flowering Plants became the most common
Animals: New mammals appeared while others became extinct, Humans are part of the most recent period in this era
Plants: Flowering Plants became the most common
Animals: New mammals appeared while others became extinct, Humans are part of the most recent period in this era