Transcript The History of Life

The History of Life
The Fossil Record
• Provides
evidence about
the history of life
on Earth.
• Shows how
different groups
of organisms,
including species
have changed
over time.
The Fossil Record

Paleotologists
• Study fossils
to infer what
past life
forms were
like.

99% of all
species that
ever lived are
EXTINCT.
Fossil Formation

Permineralization
• Occurs when
minerals carried
by water are
deposited around
a hard structure.
They may also
replace the hard
structure itself.
Fossil Formation

Natural Casts
• Form when flowing
water removes all
the original bone or
tissue, leaving just
an impression in
the sediment.
Minerals fill the
mold, recreating
the original shape
of the organism.
Fossil Formation

Trace Fossils
• Record the activity of an
organism. They include
nests, burrows, imprints
of leaves, and footprints.

Amber-Preserved
Fossils
• Organisms that become
trapped in tree resin that
hardens into amber after
the tree gets buried
under ground.
Fossil Formation

Preserved Remains
• Form when an entire organism becomes
encased in material such as ice or
volcanic ash.
Living Fossils

A living species that has remained
unchanged for tens of millions of
years
Frillshark
Cockroaches
Ants
Dragonflies
Starfish
Turtles
Opossoms
Sharks
Interpreting Fossil Evidence

Relative Dating
• The age of a fossil is
determined by
comparing its
placement with that
of fossils in other
layers of rock.
Interpreting Fossil Evidence

Index Fossils
• Are species
easily
recognized
• Found in only
a few layers
of rock in
different
geographic
locations
Interpreting Fossil Evidence

Radioactive Dating
• Radioactive elements break
down into non-radioactive
elements at a steady rate
• Scientists use this to assign
absolute ages to rocks

Half-Life
• The length of time required
for half of the radioactive
atoms in a sample to break
down.
Interpreting Fossil Evidence

C14 - Taken up by living things while alive
• After death, C14 decays to N14 (half-life of 5,730 years.)
• C12 is also taken up by living things while alive, and
does not decay after death
The more C12 there is in a sample compared to C14, the older the
sample is.
Geologic Time Scale

Scientists use the geologic time scale to
represent evolutionary time.
• As geologists studied the fossil record, they
found major changes in the fossil animals and
plants at specific layers in the rock.
Geologic Time Scale

Eras
• Scientists divide the
time into eras
• Example:




Paleozoic Era—544 mya
Mesozoic Era—245 mya
Cenozoic Era—65 mya
Periods
• Eras are subdivided into
periods, which range in
length from millions of
years to less than two
million years.
In The Beginning…
BIG BANG

12-15 billion years ago,
all matter and space was
compressed into a hot,
dense volume at one
single point.
• This incredibly hot, dense
state lasted only for an
instant, and then big bang
occurred.
• The big bang was the
instantaneous distribution
of all matter and energy
throughout the universe.
Big Bang Evidence


Radio telescopes
have detected a
relic of the big
bang—cooled,
diluted background
radiation left over
from the beginning
of time.
Telescopes have
shown that the
universe is
continuously
expanding.
Stephen Hawking proposed that
black holes formed from gamma
ray emissions following the Big
Bang.
He now suffers from ALS (Lou
Gehrig’s Disease).
Conditions on the early Earth

Between 4.6 and 4.5
billion years ago, our
Earth was formed.
• By studying other protoplanets, scientists
theorize that the Earth
began as a toxic mixture
of hydrogen gas, water,
iron, silicates, hydrogen
cyanide, ammonia,
methane, formaldehyde,
and other small organic
and inorganic
substances.
Titan, the largest moon of
Saturn.
Conditions on the early Earth

The earth did
not have a
fully functional
ozone layer at
this point and
was constantly
bombarded by
meteorites,
radiation, and
other space
debris.
Conditions on the early Earth

What about water?
• All the water that
fell on the molten
surface of the Earth
would have
evaporated at once.
• After the crust
cooled and became
solid, rainfall and
runoff eroded
mineral salts from
rocks.
Most of Earth’s early oceans were
extremely hot and had magma
just beneath the surface.
Abiotic synthesis of organic
compounds

Cells appeared less
than 200 million
years after the crust
solidified, so
complex
carbohydrates and
lipids, proteins, and
nucleic acids must
have formed by
then.
Abiotic synthesis of organic
compounds.

Synthesizing organic
compounds requires
energy.
• On the early Earth,
lightning, sunlight, or
heat from hydrothermal
vents might have fueled
the reactions.
Abiotic synthesis of organic
compounds

Stanley Miller was
the first to test
the hypothesis
that the simple
compounds that
now serve as the
building blocks of
life can form by
chemical
processes.
Abiotic synthesis of organic
compounds

Another hypothesis states
that simple organic
compounds formed in
space.
• Researchers detect amino
acids in interstellar clouds
and in come carbon-rich
meteorites that have landed
on Earth.
Abiotic synthesis of organic
compounds

Proteins, DNA, and other
complex organic
compounds break down
in open water. So how
did they form?
• By one hypothesis, the
clay of tidal flats bound
and protected the newly
forming polymers.
• Another hypothesis
proposes the first complex
biological molecules
formed near hydrothermal
vents.
Origin of the Plasma Membrane
• A current hypothesis
states that proto-cells
were transitional
forms between simple
organic compounds
and the first living
cells.
The Golden Age of Prokaryotes

Fossils indicate that the first
cells were like existing
prokaryotes; they had no
nucleus.
• There was very little free
oxygen that could attack
them.
• Anaerobic pathways would
allow them to obtain energy
from simple organic
compounds and mineral
ions.


Molecular comparisons of
living prokaryotes tell us that
some populations diverged
not long after life originated.
One lineage gave rise to
bacteria, the other archaea.
The Golden Age of Prokaryotes

Microscopically small
fossils in 3.5 billionyear-old rocks give clues
to what some of the first
prokaryotes looked like.
• 2.7 billion years ago,
colonies of prokaryotes,
called stromatolites were
abundant.
• As cyanobacteria
populations increased, so
did their waste product,
oxygen.
The Oxygen Revolution

An atmosphere
enriched with free
oxygen had two
irreversible effects.
• It helped solidify the
ozone layer.
• Aerobic respiration
evolved and in time
became the dominant
energy-releasing
pathway.
cyanobacteria
The Rise of Eukaryotes

The first complete
eukaryotic fossils are
found in rocks dated
at 2.1 billion-yearsold.
• The earliest known
eukaryote is
Bangiomorpha
pubescens. A red alga
which lived 1.2 billion
years ago.
The Rise of Eukaryotes

Eukaryotes are characterized by the
presence of organelles. So where did
they come from?
Where Did Organelles Come
From?

Endosymbiotic Theory

Some cells (parasites) struck an uneasy
balance with host cells within which they lived.
• Over time, they evolved into mitochondria,
chloroplasts, and some other organelles.
Evidence of Endosymbiosis

Mitochondria resemble
bacteria in size and
structure.
• Each has its own DNA
and divides
independently of cell
division.
• The inner membrane of
a mitochondrion
resembles a bacterial
cell’s plasma membrane.
• Its DNA has just a few
genes (37).
Evolution of Mutlicellular Life
Precambrian Time

90% of Earth’s
history occurred
during the
Precambrian
• Early life forms
developed
• Primitive multicellular
organisms appeared.
• Life existed only in the
sea
• Most animals animals
were soft bodied and
left few fossils behind.
Paleozoic Era



Rich fossil evidence shows that
early in the Paleozoic Era,
there was a diversity of marine
life.
During this period, life began
to form on dry land, including
arthropods, amphibians,
reptiles, ferns, and other
plants.
Mass Extinction
• At the end of the Paleozoic Era
about 95% of the life in the ocean
disappeared.
Mesozoic Era
Dinosaurs roamed the earth, and
flowering plants developed.
 Mass Extinction

• More than 50% of all plant and animal
groups were wiped out, including all
of the dinosaurs.
Cenozoic Era


Mammals evolved
adaptation that allowed
them to live in various
environments—on land,
in water, and even in the
air.
Homo sapiens
• Evolved 200,000 years ago
Basic Timeline of Life—Very
Approximate Dates



















3.8 billion years of simple cells (prokaryotes),
3 billion years of photosynthesis,
2 billion years of complex cells (eukaryotes),
1 billion years of multicellular life,
600 million years of simple animals,
570 million years of arthropods (ancestors of insects, arachnids and crustaceans),
550 million years of complex animals,
500 million years of fish and proto-amphibians,
475 million years of land plants,
400 million years of insects and seeds,
360 million years of amphibians,
300 million years of reptiles,
200 million years of mammals,
150 million years of birds,
130 million years of flowers,
65 million years since the non-avian dinosaurs died out,
2.5 million years since the appearance of the genus Homo,
200,000 years since humans started looking like they do today,
25,000 years since Neanderthals died out.