Transcript Unit 1 PP

Many Planets,
One Earth
Unit 1
INTRODUCTION
•Earth’s history has been constant
change
•Both the physical and biological
environments and their connections
have always been changing
•3.8 bya- simple organisms appeared
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INTRODUCTION
•2 bya- complex life emerged
•Life has endured many challenges: ice
ages, warm episodes, high/low oxygen
levels, mass extinctions, super volcanoes
erupting, and meteorite impacts
•How could life survive these hardships?
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INTRODUCTION CONT.
•Humans are new compared to the age
of the Earth
•If you scale Earth’s history down to 24
hours, we have been here for less than
half a minute before midnight.
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INTRODUCTION CONT.
•In that short period of time, we
have changed the environment
drastically.
•Even though we have done a large
amount of damage, life will go on.
•How???
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MANY PLANETS, ONE EARTH
•4.56 billion years ago, our solar
system formed from a nebula that
collapsed on itself
•Most of the matter formed the sun,
and the rest formed the planets,
asteroids, etc.
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MANY PLANETS, ONE EARTH
•The outer planets are gas because they
condensed at cooler temperatures
away from the sun
•The inner planets are called terrestrial
planets due to their rocky bodies
formed when hydrogen and helium
couldn’t condense
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MANY PLANETS, ONE EARTH
•Early Earth was not a friendly place to
be.
•Radioactivity and impacts from space
caused Earth to be extremely hot
•Earth is called Hadean after hades
during its history from 4.5 to 3.8 bya
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MANY PLANETS, ONE EARTH
• The rock during this period was melted and
recycled into the crust, so we do not have many
samples from this time
• How do we study the Earth when it was that
old???
•Meteorites that fall to Earth that are up to 4.5
billion years old can give scientists a clue into
what materials were present at the to make
the solar system.
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MANY PLANETS, ONE EARTH
• 4 bya- Earth began to moderate
• The surface cooled, allowing water vapor to condense
in the atmosphere and fall as rain
•This promoted the weathering of rock, which is part
of the carbon-silicate cycle that helps regulate
climate
• These rains created oceans around 3.5 bya
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MANY PLANETS, ONE EARTH
• On Venus, the conditions were much different
•Its average surface temp is 460 degrees Celsius
(860F) caused by the greenhouse effect of the
atmosphere
• If Venus had the same atmosphere as Earth, it would
be much colder than us due to its higher albedo
(brighter surface than Earth’s) which reflects light
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MANY PLANETS, ONE EARTH
• Mars is much colder than Earth.
• With an atmosphere 100 times thinner than Earth, it doesn’t
hold in much heat.
•Early in its history it had a denser atmosphere and could
sustain liquid water and oceans
• Earth is very unique, and it is unlikely any sort of life in
the universe is like what we have on Earth
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READING GEOLOGIC RECORDS
•The divisions of the units mark some
major change like a new life form or a
mass extinction
•Geologic time is shorter the closer you
move to present day because we have
more information to work with
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READING GEOLOGIC RECORDS
•The divisions of the units mark some
major change like a new life form or a
mass extinction
•Geologic time is shorter the closer you
move to present day because we have
more information to work with
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READING GEOLOGIC RECORDS
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READING GEOLOGIC RECORDS
• The stratigraphic record- rock layers and fossil
remains embedded in them
• This record helps scientists learn about the past
to determine two types of time scales.
• Relative time refers to sequences, what came
first or last
• Plate tectonics constantly reshape Earth,
causing the rock record to change
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READING GEOLOGIC RECORDS
• The rules for determining relative ages of rocks
are
• 1. rock are deposited horizontally
• 2. older rocks are below younger
• 3. intruding rocks are younger than the layers
they intrude into
• 4. faults are younger than the beds they cut
across
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READING GEOLOGIC RECORDS
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READING GEOLOGIC RECORDS
•Fossils also help determine relative age
•Fish evolved before mammals, so a rock
with a fish fossil is older than a rock that
contains a mammal fossil
•The environment can also leave traces on
the rock record to help form a relative age
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READING GEOLOGIC RECORDS
nd
•The 2 type of time is absolute.
•Scientists use radiometric dating to
determine the absolute age of the
rock
•This measures the decay of
radioactive isotope in the rock
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READING GEOLOGIC RECORDS
•The rocks capture the levels of certain
elements in them when the rock forms.
•Over years, unstable isotopes will decay
and lose a given amount.
•Half-life refers to the time it takes half of
the unstable isotopes to change into its
stable form.
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READING GEOLOGIC RECORDS
• Other scientific fields use our understanding of
Earth’s history
• Biologists can trace genealogical relationships
among organisms
• Climate scientists can analyze changes in
Earth’s atmosphere, temperature, and
geochemical cycle to understand why ice ages
and warming events occurred.
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CARON CYCLING AND EARTH’S CLIMATE
•Meteors and rocks stopped
raining down on Earth about
3.8 bya (the Archean eon)
•The planet then could cool and
solidify
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CARON CYCLING AND EARTH’S CLIMATE
•Water vapor condensed and fell as
rain creating oceans
•Geochemical cycle-flows of
chemical substances between
reservoirs in the atmosphere,
hydrosphere, and lithosphere
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CARON CYCLING AND EARTH’S CLIMATE
•The sun was 30% dimmer
•Earth should have been
well below freezing point of
water
•Too cold for life
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CARON CYCLING AND EARTH’S CLIMATE
•However, there is evidence of liquid
water and simple life forms 3.5 bya
•The greenhouse effect retained
enough heat from the dim sun to
keep the planet from freezing
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CARON CYCLING AND EARTH’S CLIMATE
•The Archean atmosphere was a mix
of nitrogen, water vapor, methane,
and CO2
•Volcanoes emitted the CO2
because the Earth was heating up
within the crust
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CARON CYCLING AND EARTH’S CLIMATE
•Earth could have then ended up like
Venus, but the carbon cycle saved us
•The natural sink of the carbon cycle
removes excess carbon from the
atmosphere
•The sink includes granites, basalts, etc.
located in Earth’s crust
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CARON CYCLING AND EARTH’S CLIMATE
• The carbon cycle has these basic stages
•Rainfall scrubs CO2 out of the air, making
carbonic acid (H2CO3)
•Carbonic acid reacts on contact with silicate
rocks to release calcium and leave behind
carbonate and bicarbonate dissolved in water
•This solution is washed into the oceans and
calcium carbonate (CaCO3) is precipitated in
sediments
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CARON CYCLING AND EARTH’S CLIMATE
• Over long time periods, the oceanic crust is
forced downward into the mantle at points
where the plates collide in a process called
subduction
• The limestone heats up and turns back into
CO2
• The CO2 travels back up to the surface with
magma in volcanoes
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CARON CYCLING AND EARTH’S CLIMATE
•Warmer temperature speed up this
cycle
•When the climate warms,
weathering rates accelerate and
adds carbon to rocks
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CARON CYCLING AND EARTH’S CLIMATE
•When the climate cools, weathering slows
but volcanoes continue to expel CO2
•The balance of volcanoes and adding
carbon to rocks keeps the Earth’s climate
stable
•The feedback loop can take hundreds of
thousands of years, but has never gone to
great extremes like Mars or Venus
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CARON CYCLING AND EARTH’S CLIMATE
• Venus has a large greenhouse effect because of
its lack of water to dissolve CO2
• Mars had a carbon cycle a long time ago, but
volcanism stopped putting CO2 back into the
atmosphere
• Earth has plate tectonics to continuously
recycle carbon from the atmosphere, rocks,
and to volcanoes
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TESTING THE THERMOSTAT: SNOWBALL EARTH
•Earth has had some extreme
climate episodes in its history,
including extreme glaciation
•The first Snowball Earth occurred
about 2.3 bya and others followed
between 750 and 580 mya
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TESTING THE THERMOSTAT: SNOWBALL EARTH
•Proponents of this theory believe that
Earth became so cold it froze from
equator to pole for ten millions years
or more
•They believe that eventually, the
carbon silicate cycle ended this frozen
Earth
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TESTING THE THERMOSTAT: SNOWBALL EARTH
•One possible reason for the entire
planet to freeze over is because of
continental drift
•It is believed that 750 mya the
continents clustered together in the
tropics and that had large effects on
the climate.
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TESTING THE THERMOSTAT: SNOWBALL EARTH
•If the continents were closer to the poles,
there would have been ice sheets at high
latitudes
•The Snowball Earth theory states that
since the continents grouped together at
lower latitudes, the ice sheets built up over
the oceans and reflected most of the solar
energy back to space due to ice-albedo
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TESTING THE THERMOSTAT: SNOWBALL EARTH
• If the Earth was completely frozen over, volcanoes
would still expel CO2 since they are powered by the
Earth’s core
• The continual venting of the volcanoes, plus the lack
of rain to was the CO2 out of the atmosphere, would
eventually (10 million years) bring about a warming
cycle for Earth
• Once the Earth started to warm, ice would melt and
evaporate, causing precipitation that would bring
CO2 levels back to normal
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TESTING THE THERMOSTAT: SNOWBALL EARTH
• Support for the snowball Earth scenario can be
found in the geologic record
• Glacial deposits are found on all continents at
two different times in Earth’s history (700 &
2,200 mya)
• Unusual iron formations typical of frozen
oceans and the CO2 levels are found dating
around the time of the Snowball Earth
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TESTING THE THERMOSTAT: SNOWBALL EARTH
• This frozen Earth could still have had life, called
extremophiles, inside channels in the floating
ice or around deep ocean vents
• It is possible, but not proven, that these
episodes of extreme cold fostered life forms
that were highly adaptable and those life forms
expanded quickly once the Earth warmed up
• The Snowball Earth hypothesis is still
controversial
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ATMOSPHERIC OXYGEN
•Life needs a fairly stable
climate, but also oxygen for
respiration
•Today, O2 is 20% of the
atmosphere
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ATMOSPHERIC OXYGEN
•The first 2 billion year of Earth’s
history, the atmosphere was
anoxic (no O2)
•2.3 bya, O2 was about 1% of
the atmosphere
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ATMOSPHERIC OXYGEN
•Early in Earth’s history, what little
O2 was available would have
reacted with other gases or metals
•Oxygen is highly reactive and
combines readily with other
elements
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ATMOSPHERIC OXYGEN
•Oxidation- reaction in which a
substance loses electrons and
becomes more positively
charged
•Rust forms when iron loses
electrons to oxygen
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ATMOSPHERIC OXYGEN
• Geologists can determine the levels of O2 in
Earth’s history by looking at the levels of
oxidation
• The Archean eon had little O2 in the
atmosphere because we find metals from that
eon that would normally oxidize
• 2.3 bya, there was enough O2 to form the red
bands of rock that you see in the canyons of
Arizona or Utah
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ATMOSPHERIC OXYGEN
•Cyanobacteria were the first organisms
capable of producing oxygen through
photosynthesis
•Plants producing oxygen, and animals that
respire oxygen and consume the plants,
form part of the carbon and oxygen cycle
that keeps these levels stable
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ATMOSPHERIC OXYGEN
•Sometimes material leaks out of the
cycle and alters the levels of carbon
and oxygen
•The initial rise in O2 was most likely
due to only plants producing oxygen
and little to no other organisms that
use oxygen
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ATMOSPHERIC OXYGEN
•O2 levels rose to modern levels 600
mya
•The evidence for this is that organisms
were able to grow much larger
•Organisms remain smaller if O2 levels
are low
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ATMOSPHERIC OXYGEN
• The oxygen levels of the atmosphere will remain
fairly stable, as fluctuations in either direction will
cause events that push oxygen levels back to a steady
state
• Forest fires are a negative feedback that regulate O2
levels
•The more O2 in the atmosphere, the more common
fires are
•Fires require oxygen, so many fires would reduce
oxygen levels
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EARLY LIFE: SINGLE-CELLED ORGANISMS
•Scientists know a range of when life
appeared on Earth, but not an exact
date
•Life existed at least 3 bya
•Some scientists believe rocks from
3.8 bya hold traces of early life
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EARLY LIFE: SINGLE-CELLED ORGANISMS
• The first billion years of Earth’s history had life of bacteria
and archaea
•Domains of microscopic organisms that are prokaryotes
(single celled with no nuclei)
• The tree of life branches out in the sequence in which
organisms evolved
• The lowest groups on the tree are anaerobic organisms
(survive without oxygen)
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EARLY LIFE: SINGLE-CELLED ORGANISMS
•Some bacteria and archaea are
extremophiles- can thrive in highly
saline, acidic, alkaline, hot, or cold
conditions
•Early on, microorganisms were a major
part in the Earth’s chemical cycles
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EARLY LIFE: SINGLE-CELLED ORGANISMS
•Today, they are still apart of it, but
most of the energy flow comes from
photosynthetic plants
•Cyanobacteria were found in rock
dating back 3.5 bya and jump started
these chemical cycle
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EARLY LIFE: SINGLE-CELLED ORGANISMS
•Eukaryotes are organisms with complex
cells
•Eukaryotic cells have a nucleus surrounded
by a membrane
•They contain organelles
•Endosymbiosis is a theory that explains
how eukaryotes evolved to carry out
photosynthesis
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EARLY LIFE: SINGLE-CELLED ORGANISMS
•Large cells consumed cyanobacteria but
did not digest them.
•Instead they were used to produce energy
for the new eukaryotic cell
•Mitochondria are believed to have
developed this way, since they have their
own separate DNA from the eukaryotic
cell
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EARLY LIFE: SINGLE-CELLED ORGANISMS
• The first eukaryotes appeared between 1.7 and
2.5 bya, coinciding with the rise of oxygen in
the atmosphere
• From 2.3 bya to 575 mya, life was mostly singlecelled and small
• Land was barren with no life and was
bombarded with UV rays
• Most life in this time was aquatic
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THE CAMBRIAN EXPLOSION AND THE
DIVERSIFICATION OF ANIMALS
•Multicellular fossils appear from the
late Proterozoic era (575 mya)
•Worms, jellyfish, sea pens, and
polyps (sea anemones) were the
first soft bodied multicellular
organisms
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THE CAMBRIAN EXPLOSION AND THE
DIVERSIFICATION OF ANIMALS
•These organisms grew up to a meter
across
•540 mya, the Cambrian Explosion
occurred
•The Cambrian Explosion was a period
of intense diversification of complex
life in only 50 million years
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THE CAMBRIAN EXPLOSION AND THE
DIVERSIFICATION OF ANIMALS
• The Cambrian Explosion was triggered by many
factors
•Predation spurred the evolution of
shells/armor
•Complex relationships created distinct roles
•Rising oxygen promoted larger animals
•Previous mass extinction might have created a
favorable environment for new life
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THE CAMBRIAN EXPLOSION AND THE
DIVERSIFICATION OF ANIMALS
•Phanerozoic eon (Visible Life) 540 mya to
present
•3 eras and a mass extinction between
each era
•Paleozoic
•Mesozoic
•Cenozoic
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THE CAMBRIAN EXPLOSION AND THE
DIVERSIFICATION OF ANIMALS
•Early Paleozoic life lived in the sea
•Organisms developed hard body
parts, allowing for more fossils to
be made
•Land plants emerged 500-400 mya
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THE CAMBRIAN EXPLOSION AND THE
DIVERSIFICATION OF ANIMALS
• These plants stabilized soil against erosion and
accelerated weathering of rock
• Plants decreased atmospheric carbon so much,
they are thought to have helped cause several
ice ages and mass extinctions
• The shade they provided helped the first
amphibians in their transition to land
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THE CAMBRIAN EXPLOSION AND THE
DIVERSIFICATION OF ANIMALS
•The greatest mass extinction
occurred between Permian/Triassic
boundary
•80-85% of life was wiped out
•Deep seas became anoxic (no
oxygen)
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THE CAMBRIAN EXPLOSION AND THE
DIVERSIFICATION OF ANIMALS
•The climate became suddenly warmer
and drier
•Possible causes are massive volcanic
eruptions or melting of methane
deposits that could have increased the
greenhouse effect
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THE CAMBRIAN EXPLOSION AND THE
DIVERSIFICATION OF ANIMALS
•Mesozoic era- era of reptiles
•Dinosaurs evolved in the Triassic (215
mya) and dominated for the next 150
million years
•Modern land plants emerged
(flowering plants)
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THE CAMBRIAN EXPLOSION AND THE
DIVERSIFICATION OF ANIMALS
•Small mammals and the first birds
(evolved from dinosaurs) appeared as
well
•The Mesozoic mass extinction (65
mya) killed all of the dinosaurs except
birds
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THE CAMBRIAN EXPLOSION AND THE
DIVERSIFICATION OF ANIMALS
•The meteorite that hit Earth caused:
•Shock waves
•Severe atmospheric disturbances
•A global cloud of dust cooling the
planet
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THE CAMBRIAN EXPLOSION AND THE
DIVERSIFICATION OF ANIMALS
• Evidence for this was the deposits of iridium (an
extremely rare metal from meteorites) found in
the K-T (Cretaceous-Tertiary) boundary rock
layer
• A crater in Chicxulub, Mexico’s Yucatan
peninsula, that could have been big enough to
cause this extinction
•Rocks from the region have been found
thousands of kilometers away from the site
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THE AGE OF MAMMALS
•The first mammals were rodent-sized
•They appeared during the Jurassic and
Triassic periods
•After the meteorite hit Earth and killed the
dinosaurs, mammals had less predators
and competition
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THE AGE OF MAMMALS
•Now they could radiate widely and evolve
•Most modern mammals appeared about
10 million years after the dinosaurs died
out
•Their warm bloodedness allowed them to
adapt to a wide range of temperature and
locations
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THE AGE OF MAMMALS
• Flowering plants diversified and became the
dominant land plant
• The flowers of angiosperms protected their
seeds and allowed their embryos to develop
• The flowers and fruits attracted animals to
spread their seeds and pollinate
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THE AGE OF MAMMALS
•After a quick warming period during
the Cenozoic era 55 mya, Earth cooled
down to modern temperatures
•The cooling was due to the breakup of
Gondawanaland, the supercontinent,
which formed ocean currents around
Antarctica
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THE AGE OF MAMMALS
•These currents brought cooler
water, which froze over the
continent and cooled the planet
•Climates then became dryer in
certain areas (grasslands and
deserts)
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THE AGE OF MAMMALS
•3.2 mya was Earth’s most recent ice age
•20,000 years ago was the glacial
maximum, ice sheets covered most of
Canada and extended into New England
and the upper Midwestern state
•Human evolution roughly at the same time
as this ice age
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THE AGE OF MAMMALS
•Early hominids (great apes) radiated from
earlier apes in Africa 8-5 mya
•Australopithecus (our closest ancestor)
was shorter than us and though to spend
most of its time in trees
•Homo (human genus) evolved 2.5 mya
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THE AGE OF MAMMALS
•Early humans had a larger brain,
used hand tools, and ate more
meat
•Early humans were better adapted
for life on the ground in cooler,
drier climate with expanding
grasslands
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THE AGE OF MAMMALS
• 1.9 mya, Homo erectus migrated from Africa to China
and Eurasia
•Driven by climate shifts and changes in local
environments
• Homo sapiens, modern humans, evolved in Africa
200,000 years ago
• Homo sapiens migrated from Africa following dry
land routes exposed by lower sea levels due to
glaciation
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THE AGE OF MAMMALS
•40,000 years ago, homo sapiens settled in
Europe
•10,000 years ago, they settled in North
America
•Archaeologist, anthropologists, and
geneticists are developing more precise
maps and histories of human migration
out of Africa using mitochondrial DNA
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THE AGE OF MAMMALS
•Early on, humans manipulated their
environment to survive
•Mass extinctions of large mammals
(mammoth and saber-toothed cats)
occurred in the Americas, Europe, and
Australia around the same time when
humans settled there
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THE AGE OF MAMMALS
•Early on, humans manipulated their
environment to survive
•Mass extinctions of large mammals
(mammoth and saber-toothed cats)
occurred in the Americas, Europe, and
Australia around the same time when
humans settled there
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