Transcript The History of Life

The History of Life
Unit V
Chapter 17
Fossils and Ancient Life
 A fossil is the preserved remains or evidence of an
ancient organism

Scientists who study fossils are paleontologists
 The fossil record is the grouping of similar organisms
from oldest to most recent

It can provide evidence about the history of life on Earth
and show how different groups of organisms have
changed over time
Extant v/s Extinct
 More than 99 percent of all species that have ever
lived on Earth have become extinct

The term extinct is used to describe a species that no
longer has a living representative

The term extant is used to describe a species that has
living representatives
The Formation of Fossils
 A fossil can be as large and complete as an
entire, perfectly preserved animal, or as small
as a tiny fragment of a jawbone or leaf

For a fossil to form, either the remains of the
organism or some trace of its presence must
be preserved
 The formation of any fossil depends on a
precise combination of conditions

Because of this, the fossil record provides an
incomplete record of the history of life – for
every organism that leaves a fossil, many
more die without leaving a trace
Figure 17-2 Formation of a Fossil
The Formation of Fossils
Section 17-1
Water carries small
rock particles to
lakes and seas.
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Dead organisms are
buried by layers of
sediment, which
forms new rock.
The preserved
remains may later
be discovered and
studied.
Radioactive Dating
 Radioactive dating is the use of half-lives to
determine the age of a sample


Radioactive elements decay, or break down,
into non-radioactive elements at a steady rate
called a half-life
A half life is the length of time required for half
of the radioactive atoms in a sample to decay
 In radioactive dating, scientists calculate the
age of a sample based on the amount of
remaining radioactive isotopes it contains
Formation of Earth
 Earth’s early atmosphere probably contained
hydrogen cyanide, carbon dioxide, carbon
monoxide, nitrogen, hydrogen sulfide, and
water


About 4 billion years ago, Earth cooled
enough to allow the first solid rocks to form on
its surface
About 3.8 billion years ago, Earth’s surface
cooled enough to allow water to remain liquid
 Could organic molecules evolve under these
conditions?
The First Organic Molecules
Section 17-2
Miller and Urey’s experiments
suggested how mixtures of the
organic compounds necessary
for life could have arisen from
simpler compounds present on a
primitive earth.
Mixture of gases
simulating
atmospheres of
early Earth
Spark simulating
lightning storms
Condensation
chamber
Water
vapor
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Miller and Urey produced
amino acids, which are needed
to make proteins, by passing
sparks through a mixture of
hydrogen, methane, ammonia,
and water.
Cold
water
cools
chamber,
causing
droplets
to form
Liquid containing
amino acids and
other organic
compounds
Origin of Eukaryotic Cells
 The endosymbiotic theory, championed by Lynn
Margulis, proposes that eukaryotic cells arose from living
communities formed by prokaryotic organisms
Chloroplast
Aerobic
bacteria
Ancient Prokaryotes
Nuclear
envelope
evolving
Plants and
plantlike
protists
Photosynthetic
bacteria
Mitochondrion
Primitive Photosynthetic
Eukaryote
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Ancient Anaerobic
Prokaryote
Primitive Aerobic
Eukaryote
Animals, fungi, and
non-plantlike protists
Patterns of Evolution


Macroevolution refers to the large scale
evolutionary changes that take place over long
periods of time
Six important patterns of macroevolution are:
1.
2.
3.
4.
5.
6.
Mass extinctions
Adaptive ratiation
Convergent evolution
Coevolution
Punctuated equilibrium
Changes in developmental genes
Mass Extinctions
 Extinctions occur all the time
More than 99% of all
species that ever lived are
extinct today
 Usually, extinctions occur at a
constant rate
 Several times, however,
huge numbers of species
have disappeared in
mass extinctions
 Paleontologists think that
most mass extinctions in the
past were caused by multiple
factors
 Asteroids
 Volcanic activity
 Changing position of
continents
 Changing sea levels

Adaptive Radiation
 The evolution of many diversely adapted species from a
common ancestor upon introduction to various new
environmental opportunities and challenges is called
adaptive radiation.
 Adaptive radiation typically occurs when a few
organisms make their way to new, often distant areas or
when environmental changes cause numerous
extinctions, opening up ecological niches for the
survivors.
 Fossil evidence indicates that mammals underwent a
dramatic adaptive radiation after the mass extinctions of
dinosaurs 65 mya.
Convergent Evolution
 Convergent evolution describes 2 unrelated
species that share similar traits.

These similarities are not due to common
ancestry, but rather a result of similar
environmental factors.
Coevolution
 Coevolution describes
the evolution of one
species in response to
new adaptations that
appear in another
species of which the
first shares close
interaction
Punctuated Equilibrium
 Punctuated equilibrium is a pattern of evolution in
which long stable periods are interrupted by brief
periods of more rapid change

Typically occurs when new niches become available
following a mass extinction
Developmental Genes & Body Plans
 Hox Genes are a stretch of DNA sequence
found in genes involved in the regulation of the
development (morphogenesis) of animals, fungi
and plants
 Correlations between Hox genes and major
evolutionary events are apparent…major
changes between animal phyla are correlated
with duplications in Hox genes or an increase in
the number of Hox genes
Speciation Flow Chart
Section 17-4
Species
that are
Unrelated
form
Related
in
under
under
in
in
Interrelationshiops
Similar
environments
Intense
environmental
pressure
Small
populations
Different
environments
can undergo
can undergo
can undergo
can undergo
can undergo
Coevolution
Convergent
evolution
Extinction
Punctuated
equilibrium
Adaptive
radiation
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