Fossils
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What are fossils?
The remains of animals and plants including footprints and burrows found in sedimentary rocks
In what type of rock are fossils generally found?
Sedimentary rock
What usually happens to soft tissues during fossilization?
They are eaten by other animals or decompose
What parts of organisms are most often preserved as fossils?
Bones and teeth
Why is fossilization considered rare?
The chances of an individual being preserved are very small
Why do some organisms have a better chance of fossilization?
Because of the composition of their skeletons or where they lived
What information do fossils provide?
Information about past life forms and major changes in Earth’s history
What is lost during most fossilization processes?
Soft tissues such as skin hair and internal organs
What are stratigraphic layers?
Layers formed by sedimentary rocks over time
How is the age of layers arranged in stratigraphy?
Younger layers are found on top of older layers
What does the principle of superposition state?
The oldest layer is at the bottom and the youngest at the top
How can fossils be used in relative dating?
By comparing their position in stratigraphic layers
Does relative dating give an exact age?
No it only establishes which came first
What is absolute dating?
A method that provides an actual age of a fossil
Name one method of absolute dating
Counting tree rings
What dating method uses a radioactive isotope of carbon?
Carbon dating
How old is the Earth estimated to be?
4.6 billion years old
What is the geological time scale?
A division of Earth’s history into shorter units
What are the major divisions of the geological time scale called?
Eras
What marks divisions in the geological time scale?
The appearance or disappearance of life forms in fossils
When did the Precambrian era begin?
4600 million years ago
Name one event from the Precambrian era
First signs of life
How long did the Precambrian era last?
4 billion years
When did the Paleozoic era begin?
543 million years ago