Chapter 15 Section 5 Geologic Time Scale Geologic
- Slides: 10
Chapter 15 Section 5 Geologic Time Scale
Geologic Time � Geologists study all 4. 6 billion years of the Earth’s history � Grand Canyon is one of best places to see Earth’s history in rock layers � Colorado River has eroded many layers of rock in the canyon for the past 6 million years � Can see 2 billion years (almost half!) of Earth’s history there � The rock and fossil record represent geologic time http: //commons. wikimedia. org/wiki/File: USA_09847_Grand_Canyon _Luca_Galuzzi_2007. jpg
Geologic Time Scale �Geologists use it to divide the Earth’s history into manageable parts. �Time is divided into distinct intervals � Eons – largest division � Eras – 2 nd largest, includes 2 or more periods � Periods – 3 rd largest � Epochs – 4 th largest
Important Events in Geologic Time �Archaen Eon �Earliest known rocks are formed on Earth � 3. 8 billion years ago
Important Events in Geologic Time �Paleozoic Era � First era well represented by fossils � Ended with largest mass extinction in Earth’s history �Extinction (see vocab) �Mass extinction – extinction of a large number of species in a short period of time � 90% of species were killed in this event
Important Events in Geologic Time �Mesozoic Era � “Age of Reptiles” � Reptiles (dinosaurs) dominated � Birds and small mammals begin to evolve � Dinosaurs become extinct at end of era �Possible cause = Global climate change
Important Events in Geologic Time �Cenozoic Era � “Age of Mammals” � Mammals (which evolved during last era) begin to flourish � This era is still going on �We are currently in this era!
Climate Change and Extinction �Paleontologists believe there have been at least 5 mass extinction events. �Climate change (global cooling) is thought to be the cause of these mass extinction events.
Frozen Climate History � A record of Earth’s climate is frozen in glaciers and ice sheets. � Scientists drill ice cores (cylinders of ice) to reconstruct Earth’s climate history. � Dust, soot, ash, air bubbles, and chemicals from air are trapped in the ice. � Shows scientists the composition of Earth’s atmosphere at a particular time in the past.