a trip through geologic time fossils & history of the earth - fossils
TRANSCRIPT
A Trip Through Geologic Time
Fossils &History of the Earth
- Fossils
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A Trip Through Geologic Time
Fossils and Superposition
What is a fossil?The trace or remains of an organism that lived long ago, most commonly preserved in sedimentary rock
What is a superposition?Younger rocks lie above older rocks if the layers have not been disturbed
A Trip Through Geologic Time
How a Fossil Forms
- Fossils
Most fossils form when living things die and are buried by sediment. The sediment slowly hardens into rock and preserves the shapes of the organisms.
A Trip Through Geologic Time
Fossil TypesFossil Types
1) Mold = hollow impression of a living thing in rock after it
2) Cast = solid mineral deposit that filled a mold, leaving a copy of the living thing
A Trip Through Geologic Time
Trace fossils –
Fossil Types continuedFossil Types continued
A Trip Through Geologic Time
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3) Body fossils – actual parts of an organism bones, shells, leaf imprints
Fossil Types continuedFossil Types continued
A Trip Through Geologic Time
4) Burrows or borings –
Spaces dug out by living things & preserved as is or filled in
5) Tracks –
impressions of passage of living things
Fossil Types continuedFossil Types continued
A Trip Through Geologic Time
6) Imprint –
Thin objects such as a leaf that falls onto sediment & leaves an imprint then the sediment hardens into rock
Fossil Types continuedFossil Types continued
A Trip Through Geologic Time
7) Petrified Fossils7) Petrified FossilsMinerals penetrate & replace the hard parts of an organism producing a copy of them
8) Amber & Ice8) Amber & IceAn entire organism was quickly trapped in ice or tree sap that hardens into amber
Fossil Types continuedFossil Types continued
A Trip Through Geologic Time
Where are Where are fossils found?fossils found?
Sedimentary Rock
Sedimentary Rock
A Trip Through Geologic Time
1) Hard body parts such as skeletal bones or exoskeletons
What conditions promote What conditions promote fossilization?fossilization?
2) Rapid burial and/or lack of Oxygen
A Trip Through Geologic TimeSporadoceraSporadocera
s s
NautilusNautilus
A Trip Through Geologic Time
OrthocerasOrthoceras
SquidSquid
A Trip Through Geologic Time
TrilobitesTrilobites
Lobster Lobster
A Trip Through Geologic Time
Fossil Fossil Fish Fish
A Trip Through Geologic Time
Dinosaur BonesDinosaur Bones
A Trip Through Geologic Time
Changes Over Time
- Fossils
The fossils record provides evidence about the history of life and past environments on Earth. The fossil record also shows that different groups of organisms have changed over time.
A Trip Through Geologic Time
Changes Over Time
- Fossils
From fossils, scientists have reconstructed the paleomastodon. This animal had a short trunk and short tusks on both the upper and lower jaws. The paleomastodon is an ancestor of the modern elephant.
A Trip Through Geologic Time
The Position of Rock Layers
According to the law of superposition, in horizontal sedimentary rock layers, the oldest layer is at the bottom. Each higher layer is younger than the layers below it.
- The Relative Age of Rocks
A Trip Through Geologic Time
Determining Relative Age
To determine relative age, geologists also study extrusions and intrusions of igneous rock, faults, and gaps in the geologic record.
- The Relative Age of Rocks
A Trip Through Geologic Time
Determining Relative Age
- The Relative Age of Rocks
An unconformity occurs where erosion wears away layers of sedimentary rock. Other rock layers then form on top.
A Trip Through Geologic Time
Using Fossils to Date Rocks
Index fossils are useful because they tell the relative ages of the rock layers in which they occur.
- The Relative Age of Rocks
A Trip Through Geologic Time
Index Fossil Activity
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- The Relative Age of Rocks
A Trip Through Geologic Time
Question Answer
Asking Questions
What does the position of rock layer reveal?
The oldest layers—and the oldest fossils—are at the bottom.
How do geologists determine the relative age of a rock?
They examine the position of rock layer, extrusions and intrusions of igneous rock, faults, and gaps in the geologic record.
How are fossils used to date rocks?
The age of an index fossil tells the age of the rock layer in which it occurs.
- The Relative Age of Rocks
A Trip Through Geologic Time
Determining Absolute Ages
Radioactive Decay = During radioactive decay, the atoms of one element break down to form atoms of another element.
- Radioactive Dating
A Trip Through Geologic Time - Radioactive Dating
Radioactive Decay
The half-life of a radioactive element is the amount of time it takes for half of the radioactive atoms to decay.
A Trip Through Geologic Time - Radioactive Dating
Determining Absolute Ages
Geologists use radioactive dating to determine the absolute ages of rocks.
A Trip Through Geologic Time - Radioactive Dating
Determining Absolute Ages
The age of a sedimentary rock layer can be determined relative to the absolute age of an igneous intrusion or extrusion near the sedimentary rock.
A Trip Through Geologic Time - The Geologic Time Scale
The Geologic Time ScaleBecause the time span of Earth’s past is so great, geologists use the geologic time scale to show Earth’s history.
A Trip Through Geologic Time
Earth’s Surface Forms
During the first several hundred million years of Precambrian Time, an atmosphere, oceans, and continents began to form.
- Early Earth
A Trip Through Geologic Time
Life Develops
Scientists have found fossils of single-celled organisms in rocks that formed about 3.5 billion years ago. These earliest life forms were probably similar to present-day bacteria.
- Early Earth
A Trip Through Geologic Time
Mass Extinctions
The graph shows how the number of families of animals in Earth’s oceans has changed.
- Eras of Earth’s History
A Trip Through Geologic Time
Mass Extinctions
Slightly more than 50 million years ago
Interpreting Data:
How long ago did the most recent mass extinction occur?
- Eras of Earth’s History
A Trip Through Geologic Time
Mass Extinctions
The one that occurred about 230 million years ago
Interpreting Data:
Which mass extinction produced the greatest drop in the number of families of ocean animals?
- Eras of Earth’s History
A Trip Through Geologic Time
Mass Extinctions
The number of families of ocean animals immediately dropped but then increased.
Relating Cause and Effect:
In general, how did the number of families change between mass extinctions?
- Eras of Earth’s History
A Trip Through Geologic Time - Eras of Earth’s History
Geologic History
A Trip Through Geologic Time
Continental Drift Activity
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- Eras of Earth’s History