fossils cx

7/29/2019 Fossils cx

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How old is the Earth?

SCIENTISTS BELIEVE THE EARTH WAS

FORMED

4.6 BILLION YEARS

AGO


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4.6 3.8 Billion Years Ago

The formation of our solar system


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3.8 2.5 Billion Years Ago

Earths crust was cooling and rocks and

continental plates were forming.

The atmosphere consisted mostly of

methane and ammonia.


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2.5 Billion to 543 Million Years Ago

LIFE APPEARS!!!

First fossil evidence of bacteria and later

the first eukaryotic cells.


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How can we keep up with 4.6

Billion Years of time?In order to help us work with a huge span of

time geologists have divided up the

earths history into time periods called the

Geologic Time Scale


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The Geologic Time Scale

Shows

how life has developed on Earth over time.


7/40http://geology.com/time/geologic-time-scale-550.gif


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You will see different

versions of the

Geologic Time Scale:

they arent meant foryou to memorize, but

be able to use them as

a tool.


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Precambrian Eon

Makes up 90% of Earths history.

Spans from 4.6 billion to 543 million yearsago


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These are the eras in which life

became abundant and diversified.

Paleozoic (ancient life)

Mesozoic (middle life)

Cenozoic (recent life)


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Paleozoic Era


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For example during the Mesozoic Era is

most famous for the dinosaurs that livedthen.


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Cenozoic Era Mammals are the dominant

animals: especially humans. WE ARE

STILL LIVING IN THE CENOZOIC ERA!


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Fossils


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What is a fossil?

A fossil is the remains or evidence of any

creature or plant that once lived on the

Earth.


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A fossil may be:

Bones

Teeth

The impression of a plant or animal Footprints

Burrows

Coprolite or animal feces


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Limestone matrix with 34 teeth

from same shark

http://www.fossilmuseum.net/fishfossils/Chondrichthyes-fossils.htm
http://www.fossilmuseum.net/Fossil_Galleries/Phylum_Chordata_Fossils/Class_Chondrichthyes_Fossils/Shark_Tooth_Assemblage/Shark.htm


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dinosaur tracks

www.scsc.k12.ar.us/TuttS/fossil_formation.htm
http://www.scsc.k12.ar.us/TuttS/fossil_formation.htmhttp://www.scsc.k12.ar.us/TuttS/fossil_formation.htm


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http://www.geo-tools.com/plants.htm


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Fossils are not found like assembled dinosaurs

you see in museums.


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Turtlesaur Coprolite droppings

from a turtle-like dinosaur

www.ihs.issaquah.wednet.edu/Teachers/robles/i...
http://www.ihs.issaquah.wednet.edu/Teachers/robles/in_the_classroom.htmhttp://www.ihs.issaquah.wednet.edu/Teachers/robles/in_the_classroom.htm


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Frozen baby mammoth found in the

permafrost of Siberia

goofyblog.net/news-baby-woolly-mammoth-found/
http://goofyblog.net/news-baby-woolly-mammoth-found/http://goofyblog.net/news-baby-woolly-mammoth-found/http://goofyblog.net/news-baby-woolly-mammoth-found/http://goofyblog.net/news-baby-woolly-mammoth-found/http://goofyblog.net/news-baby-woolly-mammoth-found/http://goofyblog.net/news-baby-woolly-mammoth-found/http://goofyblog.net/news-baby-woolly-mammoth-found/http://goofyblog.net/news-baby-woolly-mammoth-found/http://goofyblog.net/news-baby-woolly-mammoth-found/http://goofyblog.net/news-baby-woolly-mammoth-found/


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How are fossils formed?

No matter which way preservation occurs

it takes very special conditions. Most living

things are quickly decomposed upon

death. Scavengers and bacteria usuallyconsume all but bones and shells.


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When you think of the billions and billions of living

things that have inhabited the earth over the last

550 million years only a very small percentageare immortalized in stone!


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How do we know how old a fossil is?

Relative Dating does not give the fossils

actual age. It compares its age with fossils

or rock formations around it.


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Law of Superposition

In a sedimentary sequence, the older beds

are on the bottom and the younger beds

are on the top

C

B

A

Which is the youngest?

Layer A was deposited first


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From relative dating, we predict that layer B

is younger than A and older than C.


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Index or Guide Fossils

There were some species of organisms thatwere only around for a relatively shortperiod of time. (evolved, then became

extinct)

Therefore, when we find a rock with one of

these index fossils in it we know therelative time in which that rock wasformed.


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Examples of Index Fossils


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Absolute dating gives us the actual date of

the fossil

Most absolute dating methods use

radioactive isotopes in order to know

what an isotope is, we need to review

atomic structure.


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Radioactive Decay

the spontaneous transformation of oneelement into another.


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http://www.nrc.gov/images/reading-rm/basic-ref/glossary/radioactive-atom.gif


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By losing particles from the nucleus the

atom will become a different isotope or

another element entirely.

The original isotope is the parent.

The new isotope is the daughter.


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Examples of Radioactive

Isotopes

Parent Isotope Daughter IsotopeUranium 235 Lead 207

Potassium 40 Argon 40

Carbon

14 Nitrogen - 14


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Half-Life

Half-life is the amount of time its takes for

of the parent isotopes to turn into the

daughter isotopes.


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Example of Radioactive

Isotopes


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A fossil sample containsCarbon-14. Carbon-14 has a

half-life of 5730 years. If it hasgone through 3 half-lives, how

old is the sample?


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Geologists compare the ratio of parentelement to the daughter element to

determine the number of years ago therock was formed.

Which would be younger? a rock with agreater amount of parent, or a greateramount of daughter?

parent, because it has had less

time to decay into the daughter

element


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From measuring the ratios of the isotopes,scientists are able to determine theamount of radioactive decay that has

taken place.

Knowing the time that it takes specific

isotopes to decay gives them theabsolute date of the rock or fossilsformation.

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