Fossils, Relative Time and Absolute Time Studying the Past Fossils, Relative Time and Absolute Time

Paleontology The study of the forms of life existing in prehistoric or geologic times, as represented by the fossils of plants, animals, and other organisms.

What do you know about fossils?

Fossils Fossilis is Latin for “dug up” Fossils are the remains, molds or traces of organisms that died a long time ago Fossils are usually found in sedimentary rock like sandstone, limestone or shale

Fossils Fossils provide evidence that different organisms lived long ago Fossil organisms many times do not exist on Earth anymore They have gone extinct or they have evolved

Fossils As we go through the different types of fossils look for what each type of fossil needs to form.

5 Main Types of Fossils Original Remains Replaced Remains Molds and Casts Trace Fossils Carbonaceous Films

Original Remains Very rare Examples Most animals decay or decompose Frozen woolly mammoths Insects incased in resin (amber)

Replaced Remains Actual remains are replaced with minerals Many hard parts fossilize this way Teeth Bones Shells

Molds and Casts A replaced remain fossil may dissolve leaving behind a mold Later minerals may fill in the mold creating a cast of the original organism Click picture to see cast and mold formation

Trace Fossils Coprolites Tracks No actual part of the organism is left Give information about the location of different organisms Traces like Impressions Bite Marks Burrows Feces Coprolites Tracks

Carbonaceous Films An imprint or thin film is left behind Not the actual organism Tissue undergo chemical changes

What do fossils need to form? Sediment Compaction Water Minerals Organism TIME!!! Lots of TIME!!!

Fossil Concept Map 1. Write in the 5 fossil types 2 Fossil Concept Map 1. Write in the 5 fossil types 2. Write in a few details about each fossil type

Dating Past Geologic Events Relative Dating Example: On the way home I stopped for gas First, I ate dinner I drove home Then I went to the store Absolute Dating Example I drove home at 5:35 I stopped for gas at 5:25 I ate dinner at 5:00 I went to the store at 5:15

Dating Past Geologic Events What is the difference between these two dating methods? Relative Time has no actual times but can be put in order Absolute Time gives actual times

Relative Time Puts events in a sequence without telling when they actually happened Does not reveal actual age but age in comparison to other events

Relative Dating The evidence is in the rocks Each layer represents a different place in time Every layer of rock is another part of the timeline

Uniformitarianism “the present is the key to the past” We can watch how things happen now to understand how they happened before.

Uniformitarianism James Hutton realized these processes did not happen quickly therefore the Earth must be very old.

Uniformitarianism Siccar point in Scotland is where he made the observations Came up with the idea of DEEP TIME

Principles of Relative Dating The Principle of Superposition The Principle of Cross-Cutting Relationships Embedded Fragments

The Principle of Superposition Draw This… Water 3 2 1

The Principle of Superposition The OLDEST rock is on the bottom and the YOUNGEST is on the top Rocks are deposited horizontally

The Principle of Cross-Cutting Relationships Draw This… Water 4 2 1 3

The Principle of Cross-Cutting Relationships An igneous intrusion is YOUNGER than the rock it intrudes A fault is YOUNGER than the rock it breaks

The Principle of Embedded Fragments Water 4 3 2 1

The Principle of Embedded Fragments Rocks that are embedded in other rocks are OLDER than the rock they are found.

Unconformity Gaps in time Surfaces have been eroded away New rock has been laid on top

Unconformity

Putting in all together Rock layer correlation Matching rock in one area to rocks in another Match characteristics Match index fossils Using fossils to tell what type of environment existed

Index Fossils Fossils that can be used to identify a certain rock layer Fossils that lived within a certain time can give the rock a relative age. See page 653

Fossils Fossils can also give clues to the type of environment existed. Is there a lot of coral? Are there a lot of amphibians? Are there a lot of deep sea animals?

Relative Time Use the present to determine past processes No actual time is given Fossils can be used to indicate a general time 3 Principles