Download - 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.
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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
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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.