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FOSSILS
Provide Evidence of Change in organisms over time!
What is a fossil?
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Preserved evidence of an organisms found
This happens once they die, decompose, and
become buried with sediment
Sediments build up in layers and are subject to
intense pressure.
Therefore where will you find the oldest fossils?
Deeper in the layers of sediments
Fossil Types
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Trace Fossil- Indirect evidence Ex. Footprint, feces, burrows
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Molds and Casts- Impression or organisms
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Amber- preserved in tree sap
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Original Material- Mummification or freezing preserves
bones, teeth, skulls, etc.
What is a person called who studies fossils?
Paleontologist
How do we know how old a fossil is?
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Relative Dating- Determine dates of rocks by
comparing them with those in other layers.
 Law
of Superposition- young layers deposited on top
of old layers
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Radiometric Dating- Decay of radiometric isotopes
 Half
Life- time it takes for half
of the original isotope to decay
(Uranium 238 or Carbon 14
dating less than 60,000 yrs old)
Geologic Time Scale
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Record of Earth’s history……..more than 4 billion
years….broken into subdivision
Largest to Smallest
 Eon,
Era, Period, Epochs
The Origin of Life
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Spontaneous Generation- 1668 Francesco Redi
Tested idea that flies arose spontaneously from rotting
meat.
Observed maggots (fly larvae) appeared only in flasks
that were open to flies.
Closed flasks had no flies or maggots
 Not widely accepted
 Gave rise to biogenesis…only living organism can produce
other living organisms (Louis Pasteur)

Origin of Life: Modern Ideas
Topic of ongoing research….3 ideas all developed
due to a series of chemical events early in Earth’s
History.
1. Stanley Miller simulated Earth’s early atmosphere
and discovered organic compounds such as amino
acids, sugars, and nucleotides.
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Simulation of Earth’s Early Atmosphere
Meteorites
Panspermia is a Greek word that translates
literally as "seeds everywhere". The panspermia
hypothesis states that the "seeds" of life exist all
over the Universe and can be propagated through
space from one location to another. Some believe
that life on Earth may
have originated through
these "seeds".
Hydrothermal Vents

Hydrothermal Vents-deep sea where sulfur forms
the base of a unique food chain
What were the first cells like?
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The first cells are too old to be found as fossils so
scientists predict the first cells were:
 Prokaryotic
 Survive
in extreme environments
 Anaerobic (Oxygen present until 1.8 billion years ago)
 First Cells were photosynthesizing
 Found
fossils of Cyanobacteria that were 3.5 bil years old
 Cyanobacteria eventually produced enough oxygen to
support the formation of the ozone layer….leading to
appearance of Eukaryotic Cells!
How does the Theory of Endosymbiosis
explain the origin of Eukaryotic Cells
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Prokaryotes might have lived inside Eukaryotes
 Ingested
or internal parasites
 Relationship became mutually beneficial
 Prok. symbionts became organelles in Eurk (Chloroplast
and Mitochondria)
Evidence to support Endosymbiosis
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Mitochondria and Chloroplast have their own
circular DNA just like prokaryotes
Ribosomes that resemble those of prokaryotes
Mitochondria and Chloroplast reproduce through
binary fission just like prokaryotes
 This
theory is widely accepted
Fossils
sediments
Relative dating
Radiometirc dating
organisms
Rock layers
minerals
age
fossils
Radioactive isotopes
Check
the correct column
for each Paleozoice
statementMesozoic Era
Statement
Precambria
n
Autotrophic prokaryotes
enrich the atmosphere with
oxygen
Era
X
Primates evolve and diversify
X
It is divided into three
periods: Triassic, Jurassic,
and Cretaceous
X
Many types of insects, land
plants, and the first land
vertebrates appear
X
Mammals appear
X
Dinosaurs roam the Earth,
and the ancestors of present
day birds evolve
X
Reptiles appear
Simple organisms, such as
stromalites, live in marine
ecosystems
Cenozoic
X
X