Geologic Timeline
E.ST.06.31 - Explain how rocks and fossils are used to understand the age and geological history of the earth (timelines and relative dating, rock layers).
Geologic time from mrslarmour
Because of the time span of Earth’s past is so great, geologists use the geologic time scale to show the Earth’s history.
After Precambrian Time, the basic units of the geologic time scale are eras, periods, and epochs.
Invertebrates: organisms without backbones
Periods: range in years from tens of millions of years to less than two million years.
Epochs: What the Cenozoic Era is divided into after periods because of the extra wealth of information.
After Precambrian Time, the basic units of the geologic time scale are eras, periods, and epochs.
Invertebrates: organisms without backbones
Periods: range in years from tens of millions of years to less than two million years.
Epochs: What the Cenozoic Era is divided into after periods because of the extra wealth of information.
How to Record Geologic Time Through the Relative Age of Rocks
Relative Age: Age of rack compared to other rocks
Absolute age: Exact age of rock
Law of Superposition: in horizontal sedimentary rock layers, older rock is at the bottom. Each layer above it is younger than the rock below it.
Extrusion: Lava that hardens on the surface
Intrusion: lava that hardens and cools into the rock
Fault: A break in the Earth’s crust
Unconformity: a gap in the geologic record. Forms when one rock layer erodes and a new layer is deposited.
Index Fossils, fossils which are widely distributed in the world, are useful because they tell the relative ages of the rock layers in which they occur.
Absolute age: Exact age of rock
Law of Superposition: in horizontal sedimentary rock layers, older rock is at the bottom. Each layer above it is younger than the rock below it.
Extrusion: Lava that hardens on the surface
Intrusion: lava that hardens and cools into the rock
Fault: A break in the Earth’s crust
Unconformity: a gap in the geologic record. Forms when one rock layer erodes and a new layer is deposited.
Index Fossils, fossils which are widely distributed in the world, are useful because they tell the relative ages of the rock layers in which they occur.
Layers of Rock in the Grand Canyon. As the canyon grows deeper, older rocks are discovered (Vishnu Basement Rocks). The newest rocks are at the top of the canyon (Kiabab Formation). This demonstrates the law of superposition.