a trip through geologic time fossils & history of the earth - fossils

A Trip Through Geologic Time

Fossils &History of the Earth

- Fossils

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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


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.


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


Trace fossils –

Fossil Types continuedFossil Types continued


..

3) Body fossils – actual parts of an organism bones, shells, leaf imprints



4) Burrows or borings –

Spaces dug out by living things & preserved as is or filled in

5) Tracks –

impressions of passage of living things



6) Imprint –

Thin objects such as a leaf that falls onto sediment & leaves an imprint then the sediment hardens into rock



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



Where are Where are fossils found?fossils found?

Sedimentary Rock

Sedimentary Rock


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


OrthocerasOrthoceras

SquidSquid


TrilobitesTrilobites

Lobster Lobster


Fossil Fossil Fish Fish


Dinosaur BonesDinosaur Bones


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.


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.


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


Determining Relative Age

To determine relative age, geologists also study extrusions and intrusions of igneous rock, faults, and gaps in the geologic record.



Determining Relative Age


An unconformity occurs where erosion wears away layers of sedimentary rock. Other rock layers then form on top.


Using Fossils to Date Rocks

Index fossils are useful because they tell the relative ages of the rock layers in which they occur.



Index Fossil Activity

Web Site: PHSchool.com

Code: cfp-2042



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.



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.



Geologists use radioactive dating to determine the absolute ages of rocks.



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.


Earth’s Surface Forms

During the first several hundred million years of Precambrian Time, an atmosphere, oceans, and continents began to form.

- Early Earth


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


Mass Extinctions

The graph shows how the number of families of animals in Earth’s oceans has changed.

- Eras of Earth’s History


Mass Extinctions

Slightly more than 50 million years ago

Interpreting Data:

How long ago did the most recent mass extinction occur?



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?



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?


A Trip Through Geologic Time - Eras of Earth’s History

Geologic History


Continental Drift Activity

Web Site: Phschool.com

Code: cfp-1015


a trip through geologic time fossils & history of the earth - fossils

Documents

time fossils

geologic time fossil

geologic time changes

geologic time fossils

geologic record

disturbed slide

fossil fish slide

living thing slide