Download PPT #6 Evolution, Early Earth History

Unit 1 NOS/Evolution
ppt #6 Evolution: Early Earth History
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Earth is about 4.6 Billion years old!!
Fossil records tell the Earth’s story.
Over years many many layers of rock have
formed.
Many fossils are found within layers of
rock. Fossils are the preserved remains or
traces of organisms that lived in the past
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17-1 The Fossil Record
Interpreting Fossil Evidence
Interpreting fossil evidence to show evolution or
organisms
1. Relative Dating
Using the LAW of SUPERPOSITION:
Rock layers form in order by age—the oldest on the bottom, with
more recent layers on top.
In relative dating, the age of a fossil is determined by comparing
its placement to that of fossils in other layers of rock.
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17-1 The Fossil Record
Interpreting Fossil Evidence
Relative Dating
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17-1 The Fossil Record
In Relative dating you are comparing 1 fossil to another,
generating a history. For this you need an INDEX
FOSSIL
INDEX FOSSIL = An index fossil is a species that is recognizable
and that existed for a short period but had a wide geographic
range.
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17-1 The Fossil Record
Interpreting Fossil Evidence
Interpreting Fossil Evidence to show evolution of
organisms
2. Absolute Dating= radioactive dating
Paleontologists determine the age of fossils using the fact that
elements decay into measureable radioactive quantities.
Scientists use radioactive decay to assign an absolute
age to rocks
Using radioactive decay, C12-C14scientists can
determine true age of a fossil.
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Radioactive dating is the use of half-lives to
determine the age of a sample.
A half-life is the length of time required for half of
the radioactive atoms in a sample to decay.
17-1 The Fossil Record
Interpreting Fossil Evidence
By comparing the amounts of carbon-14 and carbon-12 in a fossil,
researchers can determine when the organism lived.
In radioactive dating, scientists calculate the age of a
sample based on the amount of remaining radioactive
isotopes it contains.
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Compare/Contrast Table
Section 17-1
Comparing Relative and Absolute Dating of Fossils
Can determine
Is performed by
Drawbacks
Relative Dating
Absolute Dating
Age of fossil with respect to
another rock or fossil (that is,
older or younger)
Age of a fossil in years
Comparing depth of a fossil’s
source stratum to the position
of a reference fossil or rock
Determining the relative
amounts of a radioactive
isotope and nonradioactive
isotope in a specimen
Imprecision and limitations of
age data
Difficulty of radioassay
laboratory methods
17-1 The Fossil Record
Geologic Time Scale
Paleontologists use a scale called the geologic time scale to
represent evolutionary time.
It is time on the scale of the history of Earth, which spans 4.6 billion
years
Scientists first developed the geologic time scale by studying rock
layers and index fossils worldwide.
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Geological time scale shows
macroevolution marked by mass
extinctions and episodic speciation.
Episodic speciation is a pattern of periodic
large scale increase in new species that
follows mass extinctions.
Compare/Contrast Table
Section 17-1
Over Earth’s History, 99.9% of all species that
have lived on Earth have become extinct, which
means that the species has died out.
Extinction means the death of an entire species.
Major Extinctions
Precambrian Extinction:
The abrupt and nearly complete disappearance of life form in late
Precambrian may have resulted from unbalanced predation, grazing, or
competition, or yet another environmental crisis such as
supercontinent breakup, changes in ocean chemistry, and/or rising
sea levels.
Whatever the causes, most species disappeared by the end of the
Precambrian, about 542 million years ago.
Their extinction, however, appears to have paved the way for a
spectacular evolution of much more familiar life, which marks the
beginning of the modern Phanerozoic Eon: the Cambrian explosion.
Cambrian Explosion
Cambrian explosion followed Precambrian
extinction. The evidence shows that nearly all
modern animal phyla, including our own chordate
phylum, are represented in this diversity of life.
Major Extinctions
Permian Extinction:
During the Permian period, all the major
landmasses of earth combined into a single
supercontinent, Pangaea. During the formation of
the supercontinent Pangaea, most marine
invertebrate species disappeared with the loss
of their coastal habitats. The Permian ended with
the most massive extinction of all time; 99.5% of
all species disappeared, opening the door for a
new radiation of species in the Mesozoic.
Major Extinctions
“K-T” (Cretaceous-Tertiary) Extinction:
The dramatic extinction of all dinosaurs (except the
lineage which led to birds) marked the end of the
Cretaceous. A collision/explosion between the Earth and
a comet or asteroid could have spread debris which
set off tsunamis, altered the climate (including acid rain),
and reduced sunlight 10-20%. A climatic shift to cooler
temperatures because of diminished solar energy coincided
with the extinction of dinosaurs.
A consequent reduction in photosynthesis would have
caused a drastic disruption in food chains. The massive
extinction and sharp geologic line led geologists to define the
end of the Mesozoic and the beginning of our modern Era,
the Cenozoic, with this event.
17-2 Earth's Early History
Formation of Earth
Evolution of THE FIRST ORGANISMS…
What substances made up Earth's early atmosphere?
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17-2 Earth's Early History
Formation of Earth
Earth's early atmosphere probably
contained hydrogen cyanide, carbon
dioxide, carbon monoxide, nitrogen,
hydrogen sulfide, and water.
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17-2 Earth's Early History
The Puzzle of Life's Origin
The Puzzle of Life's Origin
Evidence suggests that 200–300 million years
after Earth had liquid water, cells similar to
modern bacteria were common.
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17-2 Earth's Early History
The Puzzle of Life's Origin
Formation of Protocells
In certain conditions, large organic molecules like RNA form tiny
bubbles called protocells.
Protocells are not cells, but they have selectively permeable
membranes and can store and release energy.
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17-2 Earth's Early History
The Puzzle of Life's Origin
Hypotheses suggest that structures similar to protocells might have
acquired more characteristics of living cells.
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17-2 Earth's Early History
The Puzzle of Life's Origin
Evolution of RNA and DNA
How could DNA and RNA have evolved? Several hypotheses
suggest:
• Some RNA sequences can help DNA replicate under the right
conditions.
• Some RNA molecules can even grow and duplicate themselves
suggesting RNA might have existed before DNA.
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17-2 Earth's Early History
Free Oxygen
About 2.2 billion years ago, photosynthetic bacteria
began to pump oxygen into the oceans.
Next, oxygen gas accumulated in the atmosphere.
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17-2 Earth's Early History
Free Oxygen
The rise of oxygen in the atmosphere
drove some life forms to extinction,
while other life forms evolved new, more
efficient metabolic pathways that
used oxygen for respiration.
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17-2 Earth's Early History
Origin of Eukaryotic Cells
The Endosymbiotic Theory
The endosymbiotic theory proposes that eukaryotic cells
arose from living communities formed by prokaryotic
organisms.
Prokaryotes became the organelles within the Eukaryotic
cell.
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17-2 Earth's Early History
Origin of Eukaryotic Cells
Endosymbiotic Theory
Ancient Prokaryotes
Chloroplast
Aerobic
bacteria
Nuclear
envelope
evolving
Ancient Anaerobic
Prokaryote
Photosynthetic
bacteria
Plants and
plantlike
protists
Mitochondrion
Primitive Aerobic
Eukaryote
Primitive Photosynthetic
Eukaryote
Animals,
fungi, and
non-plantlike
protists
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17-2 Earth's Early History
Origin of Eukaryotic Cells
About 2 billion years ago, prokaryotic cells began evolving internal cell
membranes.
The result was the ancestor of all eukaryotic cells.
According to the endosymbiotic theory, eukaryotic cells formed from a
symbiosis among several different prokaryotes.
Eukaryotic, multicellular life evolved with sexual reproduction which
increases genetic variability. Thus…evolution of higher life
forms!
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Concept Map
Section 17-2
Evolution of first life
Early Earth was hot; atmosphere contained poisonous gases.
Earth cooled and oceans condensed.
Simple organic molecules may have formed in the oceans..
Small sequences of RNA may have formed and replicated.
First prokaryotes formed when RNA or DNA was enclosed in microspheres.
Later prokaryotes were photosynthetic and produced oxygen.
An oxygenated atmosphere capped by the ozone layer protected Earth.
First eukaryotes may have been communities of prokaryotes.
Multicellular eukaryotes evolved.
Sexual reproduction increased genetic variability, hastening
evolution.