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Outcomes:
Outcomes:
Relate the fossil record to the history of life on Earth.
Outline the order that major groups of living things appeared on earth as life evolved.
The Geological Time Scale
The Geological Time Scale
Earth's history is divided into:
Eons
Eras
Periods
Epochs
Eons are the longest subdivisions and are based on the abundance of fossils.
Eras are marked by significant worldwide changes in the types of fossils present in rock.
Periods are based on the types of existing life globally at a particular time
Epochs are divided periods characterized by differences in life forms.
Precambrian Time, which covered about 88% of Earth's history and ended about 544 million years ago, was the longest span of geological time. During this time, there were very few fossils and most Precambrian organisms lacked hard parts.
The earliest life form to appear was cyanobacteria or blue-green algae, which added oxygen to the atmosphere through photosynthesis. The time between Precambrian
Time and the present is divided into three long units called eras: Paleozoic, Mesozoic, and Cenozoic. Eras are divided into periods, named by geologists from places around the world where they found certain rocks and fossils.
What is the geological timescale and how is it divided?
What is the significance of fossils in the geological timescale?
What is Precambrian time and what can be inferred from it?
How are the different eras and periods of the geological timescale identified and named?
How has the distribution of continents changed over time and how has this affected life on Earth?
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