Download THE HISTORY OF LIFE

THE HISTORY OF LIFE
SC STANDARD B-5 Students will demonstrate an understanding
of the basis of evolution
CN: page 54 notebook
 Topic: The History of Life
 EQ: What are the 4 important patterns of
macroevolution?
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Paleontologist: scientists
who study fossils
Fossil Record:
information about past
life, including the
structure of organisms,
what they ate, in what
environment they lived,
& order in which they
lived
FOSSILS

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The fossil record
provides evidence
about the history of
life on Earth.
It also shows how
different groups of
organisms, have
changed over time.

Extinct: term used to
describe a species that
has died out
This species lived
7700 years ago
http://extinctanimal.com/extinct/exti
nct_mammals.htm
Lists of Extinct Animals

Formation of any fossil
depends on a precise
combination of
conditions
How Fossils Form

Why is the fossil
record described as an
incomplete record of
life’s history?
Evolution of Whales

Erosive forces cut
through sedimentary
rock wearing away the
youngest layers first,
exposing any fossils
embedded in them.
Interpreting Fossil Evidence

Paleontologists
reconstruct extinct
species from few fossil
bits to entire bodies.
They look for
similarities &
differences with living
organisms

In relative dating, the
age of a fossil is
determined by
comparing its
placement in the layers
of sedimentary rock
Relative Dating
Relative Dating

Index fossils: distinctive fossil used to compare
relative ages of fossils
half-life: is the length of time required for 50%
of the sample of radioisotopes to decay
 radioactive dating: calculating the age of a fossil
based on the remaining radioactive isotopes

◦ assumption is: the amount of C-14, for example, has
remained constant
◦ C-14 can only be used for fossils <60,000 yrs because
of its short half-life (not enough specimen left to
measure)
Radioactive Dating
Radioactive Decay of K-40
Geologic Time Scale
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Geologic evidence
suggests that Earth
formed over millions
of years
Process began ~4.6
billion years ago
This process involved
multiple collisions and
temperatures so high
anything solid melted

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While melted
substances arranged
themselves by densities
Less dense substances
floated to surface and
gradually cooled
forming Earth’s crust
Formation of Earth

Hydrogen & Nitrogen
formed early
atmosphere
◦
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hydrogen cyanide
carbon dioxide
carbon monoxide
sulfide
water
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~ 4 billion years ago
Earth had cooled
enough to allow 1st
solid rocks to form
still being bombarded
by comets, asteroids,
etc.
too hot for water to
exist in liquid form
Earth’s Early Atmosphere

~ 3.8 billion years ago
Earth’s surface cooled
down enough for water
to stay in liquid phase

Oceans covered most
of planet
◦ Oceans brown due to
dissolved iron
◦ Oldest sedimentary rock
deposited in water
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Miller & Urey tried to
reproduce conditions
on early Earth in a lab:
CH4 , H2 , NH3 , H2O in
a flask to represent
early atmosphere
passed electric shocks
through it to simulate
lightening
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Over a few days several
amino acids began to
accumulate
Results suggests how
mixtures of organic
cpds necessary for life
could have arisen from
simpler cpds present
on primitive Earth
The 1st Organic Molecules

Proposes that
eukaryotic cells arose
from living
communities formed
by prokaryotic
organisms
◦ Mitochondria
◦ Chloroplasts
Endosymbiotic Theory