History of Life
(Ch. 19)
The Fossil Record
Fossils and Ancient Life
Fossils are preserved remains or traces of ancient life.
Fossils are the most important source of information about
extinct species.
An extinct species is one that has died out.
Most fossils are preserved in sedimentary rock.
Sediments build up over time, and bury the remains and traces of
dead organisms.
Scientists who study fossils are called paleontologists.
What do fossils reveal about ancient life?
• FOSSILS!
– TRACE
– MOLD
– CAST
– AMBER
– IMPRINT
– PETRIFIED
Types of Fossils
• A mold is an imprint of an organism or
its trace.
• A cast fossil forms when a mold fossil is
filled with some form of mineral, usually
through the seepage of water depositing
the minerals within the mold. In time, the
mold is filled and the materials deposited
harden, creating a replica of the original
fossil. This is called a cast fossil.
•
Trace fossils give us proof of animal life
from the past. Trace fossils include things
like foot prints, burrows, and fossilized
poop.
Types of Fossils
• Amber - fossilized tree sap
• The fossils that are encased in
amber probably got there when
they flew or crawled on to the fresh
seeping sap and then got stuck. The
sap oozed over the trapped animals
and perhaps fell to the ground and
was later covered by dirt and
debris. The sap later hardened and
became a fossil.
Types of Fossils
PETRIFIED
• An exact stone copy
of an organism, the
hard parts of which
have been
penetrated and
replace by minerals.
Petrified Wood
Fish fossil
The Fossil Record
Trilobite fossil
Crayfish fossil
Dinosaur footprint fossil
Leaf fossil
Conifer leaf fossil
Dating Earth’s History
Relative dating and radiometric dating are used to
determine the age of fossils.
•Relative dating establishes the relative age of fossils.
Fossils from deeper rock layers are assumed to be older
than fossils from rock layers closer to the surface.
• Index fossils represent species that lived for a short
period of time but over a wide geographic range. Index
fossils can help determine the relative ages of rock layers
and their fossils.
• WHERE ARE FOSSILS USUALLY FOUND?
• WHO STUDIES THESE?
• HOW DO SCIENTISTS DETERMINE THE AGE OF SOMETHING
BILLIONS OF YEARS OLD?
– RELATIVE DATING
– RADIOMETRIC DATING
Dating Earth’s History
• Radiometric dating determines a fossil’s approximate age in
years by finding the proportion of radioactive to nonreactive
isotopes in a sample.
• Radioactive isotopes in fossils and rock layers decay, or break
down, at a steady rate, called a half-life.
• A half-life is the length of time needed for half of the
radioactive atoms in a sample to decay.
• A fossil’s age is calculated from the half-life and the amount of
remaining radioactive atoms the fossil contains.
Geologic Time Scale
• The geologic time scale is a time line of
Earth’s history based on relative and absolute
dating.
•The scale begins with the Precambrian.
•Geologic time is divided into four eons:
1. Hadean
2. Archean
3. Proterozoic
4.Phanerozoic.
GEOLOGICAL TIME
• Too old for years or months
• Four eras depending on which organisms
lived
• Precambrian
• Paleozoic
• Mesozoic
• Cenozoic
WHY DO WE HAVE DIFFERENT ERA’S?
PRECAMBRIAN
• WHAT DO SCIENTISTS THINK WAS ALIVE WAY BACK
THEN??
• BACTERIA
• THIS ERA LASTED FOR BILLIONS OF YEARS UNTIL MORE
LIVING ORGANISMS EVOLVED
PALEOZOIC ERA
540 MILLION YEARS AGO!!
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NOW THE EARTH IS GETTING LARGER LIFE!
FIRST PART OF PALEOZOIC IS CALLED CAMBRIAN
PROTISTS!
SEA PLANTS!
SEA ANIMALS!
LAND PLANTS!
LAND ANIMALS!
WHAT ENDED THE
PALEOZOIC ERA??
• MASS EXTINCTION!
PALEOZOIC ERA
540 MILLION YEARS AGO
MESOZOIC ERA
245 MILLION YEARS AGO!!
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DINOSAURS
REPTILES
SMALL MAMMALS APPEAR
BIRDS EVOLVE
PLATE TECTONICS
WHAT ENDED THE MESOZOIC ERA?
MASS EXTINCTION!
? METERORITE????
CENOZOIC ERA
66 MILLION YEARS AGO!
• MAMMALS FLOURISH
• PRIMATES ABOUT 30 MILLION YEARS AGO
• MODERN HUMAN SPECIES – ABOUT 200,000
YEARS AGO
Life on a Changing Planet
• Climactic, geological, astronomical, and biological processes
have affected the history of life on Earth.
• Earth’s climate has changed often in the course of its history.
• Small temperature shifts can bring about heat waves and ice
ages which have great effects on living things.
• Plate tectonics is a theory that Earth’s outermost layer is
divided into plates that move.
– The movement, called continental drift, has transformed
life on Earth through the formation of mountain ranges,
super continents, and other geologic features.
Super Continent - Pangea
Pangea - 250 million years ago
After the break up - 65 million years ago
Life on a Changing Planet
• The impact of objects from space has affected
the global climate.
Patterns and Processes of Evolution
(19.2)
Speciation and Extinction
• Macroevolutionary patterns are grand
transformations in anatomy, phylogeny,
ecology, and behavior that usually take place
in clades larger than a single species.
Speciation and Extinction
A clade is a group
consisting of an
organism and all its
descendants.
In the terms of
biological
systematics, a clade is
a single "branch" on
the "tree of life".
Speciation and Extinction
• If the rate of speciation in a clade is equal to
or greater than the rate of extinction, the
clade will continue to exist.
• If the rate of extinction in a clade is greater
than the rate of speciation, the entire clade
will eventually become extinct.
Speciation and Extinction
• Background extinction is extinction caused by
the slow process of natural selection.
• Mass extinctions affect huge numbers of
species over a relatively short time.
This graph shows how the rate of
extinction has changed over time.
Rate of Evolution
• Evidence shows that evolution has occurred at
different rates for different organisms at
different times.
• The idea that evolution occurs slowly and
gradually is called gradualism.
• In punctuated equilibrium, long periods of
little or no change are interrupted by short
periods of rapid change.
Gradualism
• Supports Darwin’s theory
Punctuated equilibrium
• Gradualism does not always hold true.
• Example – Horseshoe crabs have had very
little change in structure from the time they
appeared in the fossil record
• These organisms are in a state of equilibrium.
• Something happens to upset the equilibrium
and rapid change occurs. – Punctuated
equilibrium
Rapid Evolution After Equilibrium
– Rapid evolution may occur after a small
population becomes isolated from the main
population. This small population can evolve
faster than the larger one because genetic
changes spread more quickly among fewer
individuals.
– Rapid evolution may also occur when a small
group of organisms migrates to a new
environment. That’s what happened with the
Galápagos finches.
Adaptive Radiation
• Adaptive radiation is the process in which a
single species evolves into diverse species that
live in different ways.
This diagram shows part of the adaptive
radiation of mammals.
Adaptive Radiations in the
Fossil Record
– Dinosaurs flourished for about 150 million
years during the Mesozoic Era. The fossil
record documents that during this time,
mammals diversified but remained small.
– After most dinosaurs became extinct,
however, an adaptive radiation began and
produced the great diversity of mammals of
the Cenozoic Era.
Divergence / Adaptive Radiation
• Divergence occurs
when species evolve
in several directions
away from a common
ancestor. This happens
usually to fill a vacant
ecological niche. Also
known as adaptive
radiation.
Modern Adaptive Radiations
– Both Galápagos finches and Hawaiian
honeycreepers evolved from a single bird
species.
– Both finches and honeycreepers evolved
different beaks and different behaviors that
enable each of them to eat different kinds of
food.
Convergent Evolution
– Sometimes groups of organisms evolve in different
places or at different times, but in similar environments.
– These organisms start out with different structures, but
they face similar selection pressures.
– In these situations, natural selection may mold
different body structures in ways that perform similar
functions. Because they perform similar functions,
these body structures may look similar.
– Evolution produces similar structures and
characteristics in distantly-related organisms through
the process of convergent evolution. Convergent
evolution has occurred often in both plants and
animals.
Convergent Evolution
– Mammals that feed on
ants and termites evolved
four times in four different
regions.
– They all developed the
powerful front claws, long
hairless snout, and tongue
covered with sticky saliva
that are necessary
adaptations for hunting
and eating insects.
Coevolution
– Sometimes, the life histories of two or more
species are so closely connected that they
evolve together.
– The process by which two species evolve in
response to changes in each other over time is
called coevolution.
Flowers and Pollinators
– Coevolution of flowers and
pollinators is common and
can lead to unusual results.
–For example, Darwin
discovered an orchid whose
flowers
had
40-centimeter–About
40ayears
later,
long
structurediscovered
called a spur
researchers
with
a supply
nectar at the
a moth
with of
a 40bottom.
Darwin predicted
centimeter-long
feeding
that
some
tube
thatpollinating
matched insect
must
have some
kind of
Darwin’s
prediction.
feeding structure that would
allow it to reach the nectar.
Darwin never saw that
Plants and Herbivorous Insects
– Plants and herbivorous insects also
demonstrate close coevolutionary
relationships.
– Over time, many plants have evolved badtasting or poisonous compounds that
discourage insects from eating them.
Plants and Herbivorous Insects
– Once plants began to
produce poisons, natural
selection on herbivorous
insects favored any variants
that could alter, inactivate, or
eliminate those poisons.
– Milkweed plants, for
example, produce toxic
chemicals. But monarch
caterpillars not only can
tolerate this toxin, they also
can store it in their body
tissues to use as a defense
against their predators.
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Natural Selection : The Peppered Moth
The peppered moth is a species of
moth which uses camouflage
against tree bark to avoid being
eaten by birds. It is normally a light
grey color.
During England's industrial
revolution, pollution caused a
darkening of the bark of the trees.
There was a natural variation in
moth coloration with some being
darker than others.
Those moths of a lighter color,
were easier to spot and eat by
birds. And were eaten at a faster
rate.
The survivors tended to be darker,
and when they mated, their
offspring tended thus to be darker
also.
Over time, this resulted in the
species becoming darker in color.