Geologic Time
Life and Geologic Time
Chapter 6---Section 1
Geologic Time Scale
• Division of Earth’s history into time units
based largely on the types of life-forms
that lived only during certain time
periods
• Four major subdivisions:
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Eons (largest)
Eras
Periods
Epochs (smallest)
http://thestonescryout.com/yahoo_site_admin/assets/images/Geologic_Time_Chart.289193940_std.jpg
• The geologic time scale takes us all the
way back from present day
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Phanerozoic Eon
Cenozoic Era
Quaternary Period
Holocene Epoch
to the origin of Earth 4.5 billion years
ago during the
• Hadean Eon (Precambrian Time)
Evolution
• The process of change that occurs over
time
Lamarck’s Theory of Evolution
• Organisms pass on characteristics that
they acquired during their lifetimes to
their offspring
• Ex: He thought giraffes necks got longer
after a lifetime of eating foliage that was
very high up in trees. Each succeeding
generation would have a longer neck.
• Was his theory correct?
• NO!!!!
• Think: Does a mouse that had its tail
chopped off have a baby mouse with no
tail?
Charles Darwin
• Famous biologist who wrote a book
called The Origin of Species in 1859
• Based on what he learned during his
travels to the Galapagos Islands while
traveling aboard the HMS Beagle in the
1830s
Darwin’s Theory of Evolution
by Natural Selection
• Main points:
• Overproduction - most organisms produce
more offspring than can be supported by
the environment…not all of them can
survive
• Variation - there are many variations within
a species…those who possess the most
favorable ones have a better chance of
survival
• Natural Selection - Organisms with more
favorable variations will live longer and,
thus, have more opportunities to reproduce
• Change Over Time - If organisms with
favorable traits reproduce more than
others, then these traits will be passed on
more to future generations. If enough
changes occur in a group, a new species
may develop
Natural Selection
• The process by which organisms best
suited to the environment survive and
reproduce
• Also known as “survival of the fittest”
Modern Day Example of
Evolution by Natural Selection
• Peppered Moth - light-colored in countryside where
no pollution, but dark-colored in industrial cities
where there is a lot of dark soot from pollution on
tree trunks
• Light moths have a better chance of surviving and passing
on their white genes in the countryside
• Dark moths have a better chance of surviving and passing
on their dark genes in the city
Trilobites
• Organisms with a three-lobed
exoskeleton
• Lived in the ocean during the Paleozoic
• Are considered to be index fossils
• Different kinds of trilobites lived during
different periods. All the different types
show how trilobites evolved in response
to changes in the environment.
Species
• A group of organisms that normally
reproduces only with other members of
their group and whose offspring are
fertile
Artificial Selection
• Humans use artificial selection when
breeding domestic animals.
• By carefully breeding individuals with
desired characteristics, animal breeders
have created many breeds of cats,
dogs, cattle, chicken, etc.
What drives evolution?
• A response to major changes in:
• Type of environment
• Climate
• Caused by Earth processes or dramatic
life-changing events
• Organisms are left with two choices:
• adapt or become extinct!
Early Earth History
Chapter 6---Section 2
Precambrian Time
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Longest part of Earth’s history (90%)
Hadean, Archean, Proterozoic Eons
4.5 billion to 544 million years ago
Life-forms:
• Cyanobacteria
• Invertebrates
• Ediacaran Fauna
• May be the longest time period, but
relatively little is known about the
organisms that lived then
• Buried so deeply that they have been
changed by heat and pressure
• Have long since eroded
• Most organisms didn’t have hard parts
Cyanobacteria
• Blue-green algae thought to be one of
the oldest life-forms on Earth
• Colonies formed layered mats called
stromatolites
• Contained chlorophyll and used
photosynthesis
• Produced the first oxygen for Earth’s
atmosphere
Invertebrates
• Animals without backbones that
appeared toward the end of the
Precambrian
• Not often preserved as fossils because
of their soft bodies
• Most evidence of their existence comes
in the form of trace fossils
Ediacaran Fauna
• Group of very unusual animals with shapes
similar to modern jellyfish, worms, and soft
corals that arose late in Precambrian Time
• First found in Ediacara Hills in Australia
• Bottom dwellers
• Might have had tough outer coverings like air
mattresses
• Trilobites might have outcompeted them and
caused their extinction, but nobody knows for
sure
Paleozoic Era
• 544 million to 248 million years ago
• Traces of life are much easier to find in
Paleozoic rocks because organisms with
hard parts, such as shells, started to
become common
• Warm, shallow seas covered large parts
of continents, so there are many marine
fossils
• i.e. trilobites
• Life-forms:
• Vertebrates
• Amphibians
• Reptiles
Vertebrates
• Animals with backbones
• First ones were fishlike creatures
without jaws
• Armored fish with jaws appeared during
the Devonian
• Some were large enough to eat sharks!
Life on Land
• Many ancient fish had lungs as well as
gills
• Enabled fish to live in water with low
oxygen levels because they could swim to
the surface and breathe
• Similar creatures are alive today that can
get their oxygen from both water and air
• Some had lungs and leglike fins, which
they used to swim and crawl around on
the bottom
• Amphibians may have evolved from them
• Still had to lay eggs in moist places
• Then, some amphibians evolved an egg
with a membrane that protected it from
drying out, meaning it could be laid on
land
• These were the first reptiles
• Had skin with hard scales that prevented the
loss of bodily fluids
• Now they could live far from water
Extinction
• At the end of the Paleozoic Era
(Permian Period), more than 90% of all
marine species and 70% of all land
species went extinct
• Might have been caused by changes in
climate and lowering of sea level caused by
the formation of Pangaea
• Might have been caused by extremely high
level of volcanic activity
• Might have been caused by an asteroid or
comet impact
• Perhaps it was a combination of all these
factors
Mountain Building
• Several mountain-building episodes
occurred during the Paleozoic Era.
• This is when the Appalachian Mountains
formed.
Middle and Recent Earth
History
Chapter 6---Section 3
Mesozoic Era
• 248 million to 65 million years ago
• Pangea started to break apart during
the Mesozoic Era.
• Life-forms:
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Dinosaurs
Birds
Mammals
Gymnosperms
Angiosperms
Dinosaurs
• First small dinosaurs appeared during
the Triassic Period
• Larger species, like the Tyrannosaurus and
Apatosaurus appeared during the Jurassic
and Cretaceous
• Dinosaurs were active
• Gallimimus could run up to 65 mph!
• Some may have been warm-blooded
• Some dinosaurs nurtured their young
and traveled in herds in which adults
cared for their young.
• Ex. Maiasaura
Birds
• First appeared during the Jurassic
Period
• Some paleontologists think birds
evolved from small, meat-eating
dinosaurs.
• The earliest known bird fossil is
Archeopteryx.
• Not a direct ancestor of modern birds
Mammals
• Warm-blooded vertebrates that have
hair covering their bodies. Females
produce milk to feed their young.
• First appeared during the Triassic
Period
• Earliest mammals were small,
mouselike creatures
Gymnosperms
• Plants that produce seeds, but no
flowers
• Ex: pine and ginkgo trees
• First appeared during the Paleozoic and
dominated for the majority of the
Mesozoic
Angiosperms
• Flowering plants that produce seeds
with hard outer coverings
• Ex: magnolia and oak trees
• First evolved during the Cretaceous
Period
• Because their seeds are enclosed and
protected, they can live in many
environments
• Angiosperms are the most diverse and
abundant land plants today.
Extinction
• The Mesozoic Era ended when many
groups of animals, including the
dinosaurs, disappeared suddenly.
• Probably caused by an asteroid impact that
sent up a huge cloud of dust and smoke,
which blocked out sunlight causing many
plants to die. All the animals that
depended on these plants also died.
Cenozoic Era
• 65 million years ago to present
• The climate became much colder and
ice ages occurred.
• All the organisms that are alive today
are descendants of survivors of the last
mass extinction.
• Mammals continued to evolve and
became dominant.
Mammals
• Many kinds of mammals became larger
• Ex: horses
• Not all mammals remained on land
• Ex: ancestors of present-day whales and
mammals evolved to live in the sea
• Many species became isolated and
evolved separately from other life-forms
• Ex: marsupials in S. America and Australia
• Homo sapiens evolved around 140,000
years ago.
Mountain Building
• Many mountain ranges formed during
the Cenozoic Era.
• Alps in Europe
• Andes in S. America
• Himalayas in Asia