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Vertebrate History in Rocks (What are Fossils? (Fossils are made when a…
Vertebrate History in Rocks
What are Fossils?
Millions of years ago, fish died and there bodies turned into fossils after they decayed.This happened after a long process.
Fossils are hardened remains or other evidence of a living thing that existed a long time ago.
A fossil can be an imprint in rock.
Other fossils can be the remains of bones and other things.
Fossils are made when a chemical process takes place over time when and organism tissues are replaced by hard minerals.
Because most living tissue decays rapidly, only a very few organisms are turned into fossils.
Fossils are sometimes found in sedimentary rock.
Sedimentary rock is made when layers of sediments come together.
Sediments contain parts of clay, sand, mud or silt.
Sediments build into layers in many ways.
Its like when you wash a muddy soccer ball in the sink, and then the sink is filled with build up.
Over a very long time, layers of sediments can be pressed and cemented together to form rock.
As the sedimentary rock forms, traces of living things that have been trapped in sediments are sometimes preserved as fossils.
Interpretation of Fossils
Paleontologists are scientists who study extinct organisms, examine fossil structure and make comparisons to present-day organisms.
By studying fossils, paleontologists can infer how animals changed over time.
An important piece of information a paleontologist can learn from a fossil is its approximate age.
A Fossil's Age
One way to estimate a fossil's age uses sediments layers.
The lower layers go in first, and the higher layers settle in last.
The lower layers are older, and the higher layers are younger.
Rock layers can shift, which can make it hard to tell the age.
Since this happens, scientists mostly use other methods.
A method they use relates to radioactive chemical elements.
These elements change and decay after a known period of time.
The more decayed the element is, the older the fossil.
Using Fossils
Fossils show that the first animal living on the Earth was fish.
Fossils were on the earth about 530 million years ago.
Some patterns of change look like a branching tree.
Paleontologists use fossils to see how vertebrates have changed over time.
Amphibians which appeared on Earth about 380 million years ago came from fish.
Then, about 320 million years ago, reptiles came from amphibians.
Mammals and birds came from reptiles.
Mammals first lived on earth about 220 years ago.
Birds were the latest group of vertebrates to come.
Fossils show that birds arrived on Earth about 150 million years ago.