Our
Evolving
Planet
Life Evolves – It Changes
Everything on Earth that has ever lived is
connected through, and is the result of,
evolution.
It’s a process that’s been happening since the
first tiny life forms appeared some four billion
years ago.
Our story begins with our understanding of
time.
Geologic Time
The Earth is around 4.5 billion years old.
To help organize and understand this immense
expanse of time, scientists divide Earth’s history into
smaller chunks, such as eras and periods.
Together, these make up the geologic time scale.
– Think of the geologic time scale as the table of
contents in the history of Earth.
– The eras and periods are chapters in the story of
evolution.
– Each chapter has its own tale to tell—when life
began, when mammals first appeared, when
humans entered the scene, etc.
Precambrian Time
In Earth’s first four billion years—the time known as the
Precambrian — life first evolved, flourished, and changed the planet
forever.
- Began 4.5 Billion Years Ago -
The atmosphere contained mostly carbon dioxide, nitrogen, and
water vapor.
•Made
up of:
– Most oxygen
molecules were bound to other molecules, not free
in the atmosphere.
– You
could notEra
have breathed.
•Hadean
High levels of carbon dioxide trapped the sun’s heat, creating surface
•Archaean
temperatures
of up toEra
120 degrees Fahrenheit.
Meteorites
bombardedEra
the planet.
•Proterozoic
Volcanoes poured lava and released gases from deep inside the
Earth.
– As the lava cooled, it hardened to form the first continents.
– Volcanic steam condensed into heavy rains, which accumulated
into shallow oceans.
Origin of Life Theories
Organic
compounds
Organic compounds
may
have been
to Earth
may
havecarried
formed
on
aboard meteorites from
Earth,
perhaps in
outer space.
underwater
thermal
Scientists who study
ancient meteorites have
vents.
discovered that some
1.
2.
When
Beneath
thethe
hotocean
water
floor,
meets
cold
4.
This
charge
may
have
caused
3. contain
The hot
and
cold
waters
have
organic
chemical-rich
seawater,
dissolved
waterand
minerals
is heated
by
chemicals
to react
combine
different
chemical
make-ups,
compounds,
life’s
building
molten
precipitate
rock.
(they
Thisseparate
water
spews
out
as
inside
honeycomb-like
chambers
creating
an
electric
charge
inside
blocks.
up
solids)
through
and accumulate,
openings
in Earth’s
forming
in
the
chimney’s
walls,
forming
theSuch
chimney’s
walls.
crust.
the
vent’smeteorites
chimney. may well
organic
compounds.
have brought the raw
material of life to Earth.
First Life
By 3.5 billion years ago, tiny single-celled organisms
called prokaryotes were living in Earth’s oceans.
We find fossil evidence of these organisms in some
of the oldest rocks on Earth’s surface.
– These ancient rocks, found in Australia and Greenland,
range from 3.8 billion to 3.5 billion years old.
Photosynthetic bacteria changed the earth
dramatically.
– Used the sun’s energy to make food and water as well as
oxygen that was released into the atmosphere and the
oceans.
Endosymbiosis
Around 2.5 billion years ago, some cells began
engulfing other cells.
These cells were able to function together,
forming a new type of cell: a eukaryote.
– These different parts perform different tasks within
the cell.
Reproduction
– For billions of years by binary fission
– Later by sexual reproduction
exchanging DNA
Natural Selection
Immense, shallow oceans covered much of the planet.
Paleozoic
Era
After three billion years of evolution, Earth witnessed an
explosion of life. (AKA: Cambrian Explosion)
--Arthropods
--Sponges
--Mollusks
Cambrian and Ordovician Periods
Most animal groups living today evolved in the Cambrian
seas.
- Began
Years
– Among
the new 543
animalBillion
groups, many
hadAgo
developed
skeletons (plates, shells, and bones), backbones, and
other new features that would change the shape of life
forever.
The first mass extinction came at the end of the Ordovician Period.
– Global cooling was probably the cause.
A large landmass moved over the South Pole, causing glaciers to
form and global temperatures to cool.
Many species of trilobites, brachiopods, echinoderms, graptolites,
and corals became extinct.
– due to cooler conditions and suffered from habitat loss as water turned
to ice, lowering sea levels worldwide.
If almost all life became extinct,
then how do we know . . . .
If radiometric dating identifies the rock in layer C as 425
million years old, what can you infer about the age of the
fossils in layer C? In layers B and D? Explain.
When the
Silurian Period
began, continents
that once were
Silurian
&
Devonian
Periods
separate had come together along the equator.
Life landed ashore during the Silurian & Devonian periods.
– Plants
colonized
the continents,
creating habitats
for
the
Began
443
Million
Years
Ago
ancestors of today’s animals.
The first land plants evolved from water plants.
– green algae
Early plants had to live near water.
– Nonvascular
Movement by osmosis
Stems let plants move away from the water’s edge.
– Vascular
Movement through tissues (xylem & phloem)
Pollen and seeds broke plants’ last ties to wet
environments.
•In the seas, massive reefs — larger than at any other time in
history—covered the ocean floor, and fishes.
•The development of jaws allowed fishes and other
emerging vertebrates to catch larger prey.
•The development of tetrapods paved the way for animals
that could walk on land. (limbs and digits)
•Arthropods that evolved to live on land during this time are
ancestors of today’s insects and spiders.
•Mass extinction #2 continents had moved over the South
Pole.
•Climate too cold for many species.
•70% of life in ocean died out.
Landmasses movedCarboniferous
towards the equator and continents
began shifting from east to west.
– A resulting milder climate helped great forests
- Begins 354 billion years ago –
flourish.
Swampy tropical forests
covered
Divided
intothe continents.
– Over time and under pressure, the remains of these
forests would become the great coal fields mined for
fuel we use today.
Mississippi and Pennsylvanian
Fossils tell us arthropods and tetrapods thrived here
(some were giants).
--insects --millipedes
--arachnids
Permian
Earth’s continents had assembled into one giant landmass called Pangaea.
Three basic environments:
--arid
--tropical
--temperate
- Began 290 Million Years Ago -
Ever-increasing diversity of plant and animal life.
Tetrapods that waded ashore in previous periods diversified into to two new
groups.
– Reptiles
Amniotic Egg
– Synapsids
Ancestor of Mammals
– Third mass extinction at the end.
Global warming (volcanic activity)
Nearly wiped out all life on earth
– 90% of Marine Animals died out
– 80% of Land Animals died out
This era saw the evolution of the largest animals to
have ever walked the earth.
Mesozoic
– Called the Age of Dinosaurs
– They would give rise to birds.
– Crocodiles,
snakes,
and
turtles making
their
first
Began
248
Billion
Years
Ago
appearance.
The emergence of mammals,
from which humans
Divided into
eventually evolved.
The emergence of birds, which are the living dinosaurs
of today.
Triassic
The emergence of flowing plants, which created rich
Jurassic
and varied habitats where
new forms of life could
evolve and diversify.Cretaceous
– Angiosperm
4th Mass Extinction
– Early Mesozoic
Volcanic Activity lead to global warming.
–50% of Marine Life went extinct
5th Mass Extinction
– Late Mesozoic
– Possible Meteorite
50% of all Life went extinct
Age of Mammals
– hoofed mammals, rodents, and carnivores evolved
– First warm tropical forests, then cooler, drier grasslands provided
rich habitats where mammal species could thrive and diversify.
Cenozoic Era:
Tertiary
– Three types of mammals:
Monotremes - hatch Period
from eggs.
Marsupials - are born before they are fully developed and
continue development outside the womb, often in a pouch.
Placentals - develop completely in their mother’s wombs
before they are born.
– also grouped by differences in their features
Claws/Hooves
Teeth Differences (eating)
Grasping Hands & Feet
- Began 65 Million Years Ago -
The Age of Early Human
Primates
– Grasping Hands & Feet
– Forward Facing Eyes (depth perception)
– Large Brain (in relation to rest of body)
Humans belong to the primate group called
hominids.
– First appeared eight million years ago.
– Evolved from an ape ancestor.
did not all evolve in a single direct progression from apes
– Evolved through the same unpredictable process as
every other living thing
Telling Hominids
&
Apes Apart
1. Skull
6.
3.
4.
5.
Pelvisarches
Femur
Foot
2. Toes
Teeth
The opening for an ape’s spinal
An
ape’s
big
toe
istall
splayed
off to
An
ape’s
pelvis
femur
foot
is
is
(upper
flat.
and
leg
narrow.
bone)
An
ape’s
canine
teeth
are
column is towards the back of the
the
side.straight
This
thumb-like
toe is
extends
down.
relatively
large.
skull, so the spine extends
great
for grasping,
but not
for
A
human’s
shorter
foot
is
arched,
and
wider
backwards and down.
weight
bearing.
pelvis
A
absorbing
makes
shock
femur
for when
more
isteeth
angled
stable
theare
foot
A hominid’s
hominid’s
canine
walking
inward,
falls.
positioning
oncomparison.
two
the knees and
smaller
by
The opening
for legs.
a hominid’s
A
human’s
big
toe is
lined
up
feet
directly
under
the
body’s
spinal column is at the bottom of
parallel
with
the other
toes,
bearing
center
of
gravity
during
walking.
the skull, so the spine extends
the weight of the body during the
directly down underneath the
“push-off” to the next step.
skull.
Australopithecines
One of the earliest hominids
– Smaller than the average modern human
– Smaller brains
– Protruding jaws
– Large molars
grinding down tough plant material
– Walked upright
some probably spent time in trees
The female hominid, a young adult named
“Lucy”, lived in eastern Africa 3.2 million
years ago.
Homo ergaster
Earliest species of the genus Homo
First appeared in Africa
– around 2 million years ago
The first true humans
– Characteristics:
Larger brains
Flatter faces with projecting, flat, noses
Smaller teeth
– Could now eat meat
Larger with shorter arms and longer legs
A life spent completely on the ground, not in the trees
Key Trends in Hominid Evolution
Leaving the trees and walking on land
Bigger brains relative to body size
– more sophisticated thinking processes
Remnants of primate body parts that we
no longer use
Remnants
Wisdom teeth
– Needed for chewing to break down plants
Third eyelid
– Small pink fold in the inner corner of the eye
– Helped keep eyes clean.
Reptiles have this membrane too, so we have a common ancestor
Ear wiggling muscles
– Early primates could move their ears independently
cats and dogs
Palmaris muscle
– long, narrow muscle that runs from wrist to elbow
important for climbing and hanging
about 11% of us are missing this
Goosebumps
– Muscle fibers that make your hair stand on end
When cold or scarred
Early primates used for insulation or to intimate
Fifth toe
– For grasping or clinging to branches.
– Big toe used for balance
Climate Shapes Evolution
Homo sapiens VS Neanderthals
Homo sapiens
– Originated in Africa 195,000 years ago
– Slender body great for warm environment
Neanderthals
– first evolved in Europe, at least 400,000 years ago.
– Stockier body to help retain heat
Neanderthals were our neighbors, not our ancestors.
Quartenary
Commonly known as the Ice Age
Changing climate and the formation of new land
- Began 1.8 Million Years Ago bridges.
– Dramatically affected the evolution of
mammals
Led to diversity
Mammals became massive
Continents moved to their current locations
Glaciers at the poles
6th Mass Extinction
HUMANS
For the first time in Earth’s history, a
single species is the primary cause of a
mass extinction.
ARE
THAT
SPECIES!
Sources
http://www.fieldmuseum.org/evolvingplane
t/exhibition.asp
http://evolution.berkeley.edu/evolibrary/article
/0_0_0/evo_13