Transcript 2. PreCambrian time to Present

A View of Earth’s Past
PreCambrian Time - Present
Chapter 9
Sections 2 & 3
Introduction
• The rock and fossil records show that Earth changes
over time. One of these changes allowed the
Oxygen we breathe to begin accumulating.
• The geologic history of Earth is recorded in rock
layers. The types of rock and fossils occurring in each
layer reveal info about the environment when the
layer formed.
• A limestone layer in an area indicates that area was
once covered by water.
Evolution
• Fossils indicate the kinds of organisms that lived
when the rock formed. Examination of this evidence
led to the discovery that species change over time.
This process is evolution.
• This is gradual development of new organisms from
pre-existing ones. Scientists think that evolution
occurs by natural selection.
• Theory of Natural Selection was proposed in 1859 by
Charles Darwin.
• Evidence includes similarity in skeletal structures.
Skeletal Similarities
PreCambrian Time
• This is the time interval between the formation of
earth and ended about 542 mya.
• This makes up about 88% of Earth’s history.
• We know very little about this part of Earth’s history
because the rocks are so severely deformed
PreCambrian Rocks
• Large areas of exposed PreCambrian rocks called
shields exist on every continent except Antarctica.
• They are the result of several hundred million years of
volcanic activity, mountain building, sedimentation
and metamorphism.
• Nearly half of the valuable mineral deposits in the
world occur in rocks of Precambrian shields, including
Nickel, Iron, Gold and Copper.
PreCambrian Life
• Fossils are rare due to PreCambrian life forms lacking
backbones , shells or other hard parts that commonly
form fossils.
• Some PreCambrian rocks date back over a billion years
and volcanic activity, erosion and extensive crustal
movement have probably destroyed most fossils.
• Stromatolites are layered, reeflike deposits that form in
shallow warm water. These hold cyanobacteria. Their
presence indicates shallow seas covered much of the
earth at this time.
• Fossils include: Marine worms, jellyfish, and single celled
organisms.
Stromatolites
Paleozoic Era
• Began about 542 mya and ended about 251 mya.
• Earth’s landmasses were scattered around the world, but
by the end they had collided to form pangaea. Creating
new mountain ranges and lifting large areas above sea
level
• Paleozoic rocks contain abundant fossils because the
number of plant and animal species increased
dramatically.
Cambrian Period
• A variety of marine life forms appeared during this
period and being more advanced, they quickly
became the dominant life forms.
• This explosion of life may have
been due to the warm, shallow
seas covering much of the
continents during this time.
• Trilobites are the main index
fossil for this time.
Ordovician Period
• Number of Trilobite species decreases, Brachiopods,
Bryozoans, and Cephalopod Mollusks become
dominant life forms. Large
numbers of corals appear and
Graptolites
flourish in the oceans.
• Vertebrates appear- most
primitive are the fish. They had
no jaws or teeth, bodies covered
by thick bony plates.
• There is little plant life on land
Graptolites
Silurian Period
• Vertebrate and Invertebrate marine life are thriving.
• Echinoderms (relatives to sea stars) and corals are
more common.
• Eurypterids, scorpion like sea creatures also existed.
Fossils of giant eurypterids (2m long) have been
discovered in western NY.
• Early vascular land plants as well as animals, such as
scorpions evolved on land.
Carboniferous Period
• Climate generally warm and humidity was very high over
most of the world.
• Forests and swamps cover much of the land. Coal
deposits in PA, OH and WV are the fossilized remains of
these forests.
• Carboniferous means “carbon bearing”
• Amphibians and fish continue to flourish. Crinoids are
common in the oceans, giant cockroaches and
dragonflies are common on land.
• Toward the end of this period, vertebrates adapted to life
on land appeared. These early reptiles resembled large
lizards.
Mesozoic and Cenozoic Eras
• Mass Extinction- an episode where an enormous
number of species die. At the end of the
Permian Period, 90% of marine organisms and
more than 70% of land organisms died.
• This left many resources and space available and
an abundance of new life forms appeared.
• These new life forms evolved. Some flourished
while others eventually became extinct.
Mesozoic Era
• Began about 251 mya and ended about 65 mya.
Divided into 3 periods
• Earth’s surface changed dramatically during this
time. Pangaea broke into smaller continents,
tectonic plates drift and collide.
• The Sierra Nevada mountains in CA and the Andes in
South America were uplifted. Shallow seas and
marshes covered much of the land. Climate is warm
and humid. Rich fossil record.
• Conditions favored survival of Reptiles. This era is
known as the Age of the Reptiles.
Mesozoic Era
Triassic Period
Jurassic Period
Cretaceous Period
Lizards, turtles, crocodiles and a variety of
dinosaurs flourished.
Triassic Period
• Dinosaurs the size of squirrels to those weighing 15
tons. Most were about 2-5m long and quick moving.
• They roamed through lush forests of cone-bearing
trees and cycads
• Reptiles called ichthyosaurs lived in the oceans.
Ammonites evolved and serve as the index fossil for
this era.
• The first mammals, small rodent-like forest dwellers,
appeared.
Jurassic Period
• Dinosaurs become the dominant life form. Fossils
indicate 2 major groups, distinguished by their hip
structure.
– Saurischians (lizard hipped) herbivores and
carnivores, includes Brontosaurus, 15 tons, 25m
long.
– Ornithischians (bird hipped) herbivores, best
known is Stegosaurus, 9m long and 3m at the
hips.
Flying reptiles, pterosaurs were common. Had skin
covered wings.
Archaeopteryx
Cretaceous Period
146- 65.5 million years ago
Dinosaurs continue to dominate earthT-rex stood nearly 6m tall and had huge jaws and
sharp teeth nearly 15cm long.
Ankylosaurs were armored and Ceratopsians were
horned and the Hadrosaurs are duck-billed.
Plant life is becoming more sophisticated- angiosperms
(flowering plants) appeared, most common are the
magnolia and willow, larger trees including the
maples, oaks and walnuts become abundant.
Cretaceous- Tertiary Mass Extinction
The Cretaceous Period ended in another mass extinctionNo dinosaur fossils have been found in rocks formed
after this period.
Impact Hypothesis- approximately 65 mya an asteroid
crashed into Earth, the impact raised enough dust to
block the sun ray’s for many years. The climate became
cooler, plant life began to die and many animal species
became extinct. As the dust settled it formed a layer of
iridium-laden sediment. Iridium is an element found
only in meteorites and not on earth.
The Cenozoic Era
65.5 mya- present time Age of Mammals
Includes the periods- Tertiary and Quaternary which
are broken down into epochs
Continents are moving to their present day locations,
tectonic plates collide forming the Alps and the
Himalayas in Eurasia.
Had dramatic changes in climate, at times ice sheets
covered nearly 1/3 of Earth’s land. Decreasing temps
brought about new species and mammals became
the dominant life-form undergoing many changes.
Tertiary & Quaternary Periods
These periods have been divided into 7 epochs
The Tertiary Period includes the time before the last
Ice Age (approx 10,000 years ago)
Epochs: Paleocene, Eocene, Oligocene,
Miocene, and Pliocene
The Quaternary Period began with the last Ice Age and
Includes the present.
Epochs- Pleistocene and Holocene
Tertiary Period
Paleocene and Eocene EpochsFossil record indicates that during the Paleocene many
new mammals such as small rodents evolved and the
first primates appeared.
During the Eocene the earliest know ancestor of the
horse evolved and the 1st whales, flying squirrels and
bats appeared. Small reptiles continue to flourish.
Worldwide temps dropped by about 4⁰C at the end of
the Eocene.
Paleocene and Eocene life
Tarsier is sole survivor of
the Cenozoic primates
Tertiary Period
Oligocene and Miocene Epochs
During Oligocene the Indian subcontinent collided with
the Eurasian continent and caused the uplifting of
the Himalayas. Worldwide climate became
significantly cooler and drier which favored grasses
and hardwood trees. Many early mammals became
extinct, but large species of deer, horses, pigs, cats
and dogs flourished.
Marine invertebrates including the snails and clams
flourished
Tertiary Period
Oligocene and Miocene Epochs
During the Miocene, circumpolar currents formed around
Antarctica and the modern Antarctic ice cap began to
form. By the end of the Miocene the Mediterranean sea
had dried up and refilled several times due to tectonic
forces and sea levels falling.
Largest known land mammals existed during this epoch and
fossils can be found of horses, deer, camels,
rhinoceroses, pigs, raccoons, wolves, foxes, and the
earliest saber-toothed cats. Earliest human ancestors
may date to this epoch.
Oligocene and Miocene Life
Tertiary Period
Pliocene EpochPredators from the bear, dog and cat families evolved into
modern forms. Herbivores like the giant ground sloth
flourished and modern day horses appeared.
Toward end of Pliocene, climate changes occurred and
continental ice sheets spread locking more and more
water in the ice so sea level fell. The Bering land bridge
appeared between Eurasia and North America. The
Central America land bridge also formed and various
species could migrate across the 2 bridges.
Quaternary Period
Pleistocene Epoch- began about 1.8 mya.
In NA and Eurasia ice sheets advanced and retreated
several times. Some animals with thick fur (wooly
mammoths and rhinos) could survive the cold, some
moved further south to warmer regions. Some
species became extinct like the giant ground sloths
and the dire wolves.
Fossils of earliest modern humans (Homo sapiens) are
discovered in Pleistocene sediments. Cave paintings
show that early humans may have been hunters.
Quaternary Period
Holocene Epoch- This epoch includes the
present and began about 11,500 years ago at
the end of the last Ice age. As the ice sheets
melted sea level rose about 140m and the
coastlines took on their present shapes. The
Great Lakes formed as the ice sheets
retreated. Modern humans developed
agriculture and started making bronze and
iron tools.
Think About This
Compared to Earth’s entire history, human history is
extremely short.
If you think of earth’s history as 1 year:
September- 1st multi-cellular organisms appear
December 26, 8:00pm- Dinosaurs disappear
December 31, 11:48pm- Modern humans appear
Other ways to think of Earth’s history- a clock…