GEOLOGIC TIME SCALE

GEOLOGIC TIME The divisions are: 1. EONs (largest) 2. ERAs 3. PERIODs 4. EPOCHs (smallest) None of these are specific amounts of time. Change when life changes on Earth.

4 Eras Precambrian Era Paleozoic Era Mesozoic Era Cenozoic Era

GEOLOGIC TIME SCALE: model of the geologic history of the Earth (4.5 billion years) It is mainly based on rock and fossil evidence. EXAMPLE: Major group of organisms becomes extinct - new time interval (66 million years age = end of the Mesozoic Era or beginning of the Cenozoic Era) Dinosuars became extinct (no more fossils)

4 Eras Precambrian Era Paleozoic Era Mesozoic Era Cenozoic Era

Precambrian Era Significant Events 4.5 billion to 570 million years ago First oxygen (2.5bya) allowed simple life forms to emerge (1.8 bya)

Paleozoic Era Significant Events 570mya-249mya (million years ago) Mainly sea life (invertebrates, fishes, amphibians) Pangaea forms at the end of the era

Mesozoic Era Significant Events 248mya-66mya Reptiles are the dominant species Dinosaurs went extinct at the end Pangaea breaks up at the end of the era.

Cenozoic Era Significant Events 65mya-present day Mammals are the dominant species Plate Tectonics, earthquakes, mountain building volcanism all occur and continue to occur.

Geologic Time North Carolina Linda Kennedy, Department of Geography, UNCG, July 2011

Relative Dating- determine the age of a rock layer based on it’s position in rock strata Superposition-Rock layers on the top are the youngest, rock layers get progressively older as you go down in layers.

Using Fossils When we find the same kinds of fossils in rocks from different places, we know that the rocks are the same age. Index Fossils help to correlate rock structures and their (geologic time era or period) ages.

The fossil record is incomplete (not all the organisms that have lived are fossilized)