Earth’s History
CHAPTER 13
Earth’s History – Chapter 13
I. Precambrian Time: Vast and Puzzling
A. Precambrian History
1. Precambrian Rocks
2. Earth’s Atmosphere Evolves
3. Precambrian Fossils
II. Paleozoic Era: Life Explodes
A. Early Paleozoic
1. Early Paleozoic History
2. Early Paleozoic Life
B. Late Paleozoic
1. Late Paleozoic History
2. Late Paleozoic Life
C. The Great Paleozoic Extinction
III. Mesozoic Era: Age of Reptiles
A. Mesozoic Era
1. Mesozoic History
2.Mesozoic Life
3. The Shelled Egg
4. Reptiles Dominate
IV. Cenozoic Era: Age of Mammals
A. Cenozoic North America
B. Cenozoic Life
1. Mammals Replace Retiles
2. Large Mammals and Extinction
Precambrian History
oThe Precambrian encompasses immense geological time, from Earth’s
distant beginnings 4.56 billion years ago until the start of the Cambrian
period, over 4 billion years later.
oThe Precambrian comprises about 88% of the Geologic Time Scale.
oMost Precambrian rocks do not contain fossils. This makes correlating
rocks difficult.
oMost rocks during this age are metamorphosed and deformed, extremely
eroded, and hidden by overlaying strata.
Precambrian Rocks
o The lack of Precambrian Rock illustrates the law of superposition.
oPrecambrian Rocks are buried from view underneath more recent rocks.
oPrecambrian Rocks only show through the surface where younger strata
are extensively eroded.
oExamples: The Grand Canyon and Mountain Ranges
o Large core areas of Precambrian Rocks dominate the surface of some
continents, mostly deformed metamorphic rocks.
oShields are large, relatively flat expanses of ancient metamorphic rock
within the stable continental interior.
oMuch of what we know about Precambrian rocks comes from ores mined
from shields.
oThe mining of iron, nickel, gold, silver, copper, chromium, uranium and
diamonds have provided rock samples of Precambrian time.
Earth’s Atmosphere Evolves
o Early in Earth’s History, the high velocity impact of nebular debris caused
the outer shell of our planet to melt.
oEarth then slowly cooled and the surface solidified into the crust and
gases were dissolved.
oEarth’s original atmosphere was made up of gases similar to those
released in volcanic eruptions today- water vapor, carbon dioxide,
nitrogen, and several trace gases, but no oxygen.
oAs Earth continued to cool, the water vapor condensed to form clouds
and rain began.
oThe first life forms on Earth did not need oxygen.
oPrimitive organisms evolved that used photosynthesis and released
oxygen.
oThese organisms influenced Earth’s atmosphere- they used carbon
dioxide and produced oxygen.
oSlowly, the oxygen content increased on Earth
oOxygen began to accumulate in the atmosphere about 2.5 billion years
ago.
Precambrian Fossils
o The most common Precambrian fossils are stromatolites.
oStromatolites are distinctively layered mounds or columns of calcium
carbonate.
oThey are NOT the remains of actual organisms but are material deposited
by algae.
oStromatolites are indirect evidence of algae because they closely
resemble similar deposits made by modern algae.
oStromatolites were commonly found in the middle Precambrian time.
oMany ancient fossils are preserved in chert.
oChert is hard, dense chemical sedimentary rock.
oChert must be sliced very thin and studied under a powerful microscope.
oThese fossils are the most primitive organisms, called prokaryotes.
oMore advanced organisms called eukaryotes evolved later.
oThe development of eukaryotes has dramatically increased the rate of
revolutionary change.
oWe start to see animal fossils in the late Precambrian in the form on trace
fossils.
Earth’s History Section 2
II. Paleozoic Era: Life Explodes
A. Early Paleozoic
1. Early Paleozoic History
2. Early Paleozoic Life
B. Late Paleozoic
1. Late Paleozoic History
2. Late Paleozoic Life
C. The Great Paleozoic Extinction
Paleozoic Era: Life Explodes
oFollowing the long Precambrian, the most recent 540 million years of
Earth’s history are divided into three era: Paleozoic, Mesozoic and
Cenozoic.
oThe Paleozoic Era encompasses about 292 million years and is the longest
of the three eras.
oThe Paleozoic Era contains many more diverse fossils due to the
emergence of life forms with hard parts (shells, scales, bones or teeth)
oThis allowed for a far more detailed section for the remaining 1/8 of the
Geologic Time Scale.
Divisions of the Paleozoic
The Paleozoic Era is divided into sub-categories (periods).
◦ Early Paleozoic is divided into Cambrian, Ordovician and Silurian
Periods
◦ Late Paleozoic is divided into Devonian, Mississippian, Pennsylvanian
and Permian Periods
Early Paleozoic
oEarly Paleozoic consists of 123 million years.
oIncluding Cambrian, Ordovician and Silurian periods
oDuring the Cambrian, Ordovician and Silurian periods, the southern
continent of Gondwana encompassed five continents
oSouth America, Africa, Australia, Antarctica and parts of Asia
oNorth America and other continents were not a part of Gondwana. The
exact location is uncertain but we assume it is somewhere near the
equator and separated by a narrow sea.
oDuring the Paleozoic Era North America was a land with no living things,
plants or animals.
Early Paleozoic Life
oLife in early Paleozoic time was restricted to the seas.
oVertebrates had not yet evolved, so life consisted of several invertebrate
groups.
oThe Cambrian period was the golden period of trilobites.
oMore than 600 types of these mud-burrowing scavengers flourished
world-wide.
Ordovician Period
oIn the Ordovician period, brachiopods outnumbered the trilobites.
Brachiopods are among the most widespread Paleozoic fossils
oThe Ordovician period also marked the appearance of cephalopodsmobile and highly developed mollusks that became the major predators.
oSquid and octopus are descendents of these early cephalopods.
oCephalopods were the first truly large organisms on Earth.
Cambrian Period
oThe beginning of the Cambrian period marks an important event in the
animal evolution.
oOrganisms appeared that secreted material that formed hard parts, such
as shells
oHard parts clearly served many useful purposes and aided adaptions to
new ways of life.
oThe development of exoskeletons began.
Late Paleozoic
oThe late Paleozoic consists of four periods.
oDevonian, Mississippian, Pennsylvanian and Permian
oThis span was about 160 million years.
oTectonic forces reorganized Earth’s landmasses during this time, creating the
supercontinent Pangea.
Late Paleozoic History
oNorth America and Africa collided, the narrow sea between the two began to close.
oStrong forces of compression deformed the rocks to produce the Appalachian
Mountains of eastern North America.
oBy the Permian period, a newly formed landmass was created by the collision of
western Asia and the Siberian landmass. This landmass is
called Laurasia.
oBy the Pennsylvanian period, Laurasia formed and
Gondwana moved north. The Gondwana collided with
Laurasia forming a mountain belt in Europe.
oBy the end of the Paleozoic Era, all the continents had
fused together into the supercontinent Pangea.
Late Paleozoic Life
oSome 400 million years ago, plants that had adapted to survive at the
water’s edge began to move inland, becoming land plants.
oThe earliest plants were leafless vertical spikes about the size of an index
finger.
oBy the end of the Devonian period, 40 million years later, the fossil record
indicated the existence of forests with trees tens of meters high.
oIn the oceans, armor-plated fish evolved during the Ordovician period
adapted in the Devonian period.
oOther fish evolved during the Devonian period, including sharks and most
modern fish we see now. Because of these drastic evolutionary changes
we call the Devonian Period the ‘Age of Fishes’
oBy the Pennsylvanian Period, large tropical swaps extended across North
America, Europe and Siberia. Trees are growing. Coal deposits originated.
Amphibians evolved quickly.
The Great Paleozoic Extinction
o The Paleozoic Era ended with the Permian period. At this time the land
was getting more dry. There were changes in the lands elevation and
overall changed the climates.
oClose to the Permian, 75 percent of the amphibian families had
disappeared. Plants had declines in number and variety.
oMuch of marine life did not adapt and survive. 80%-95% of marine life
disappeared.
oMany marine invertebrates that were dominant during the Paleozoic Era
including trilobites, coral and brachiopods could not adapt.
o The late Paleozoic extinction was the greatest of five mass extinctions to
occur over the past 500 million year.
oHowever, survivors forming new biological communities
oThis mass extinction allowed life on Earth to flourish.
oThe cause of the Paleozoic extinction is uncertain, but it is clear that
without it a very different population of organisms would exist today.
Section 3- Mesozoic Era
III. Mesozoic Era: Age of Reptiles
A. Mesozoic Era
1. Mesozoic History
2.Mesozoic Life
3. The Shelled Egg
4. Reptiles Dominate
Mesozoic Era
oThe Mesozoic Era spanned about 183
million years and is divided into three
periods. Triassic, Jurassic and Cretaceous.
oThe Mesozoic Era marked the beginning of
the breakup of the supercontinent Pangea.
oOn land, dinosaurs became dominant and
were unchallenged for over 100 million
years.
Mesozoic History
o The Mesozoic Era began with much of the land above sea level. Very few
marine fossils were found during the Triassic period.
oIn the beginning of the Cretaceous Period, the shallow seas became swamp-like
areas where coal deposits formed becoming important to the United States now.
oFollowing the beginning of Pangea’s breakup, a rift developed between what is
now the United States and Africa. This rift becomes the Atlantic Ocean.
oPangea took 200 million years to breakup into what the continents are now.
Mesozoic Life
o Life forms that were present during the Mesozoic Period were the only
life forms that survived the Paleozoic extinction.
oGymnosperms, a group of seed-bearing plants that did not depend on
free-standing water for fertilization. This plants were some of the few
plants that could survive in a drier climate.
oGymnosperms quickly became the dominant plants of the Mesozoic.
oConsisted of: Cycads, Conifers and Ginkgoes.
The Shelled Egg
oReptiles readily adapted to the drier
Mesozoic environment.
oReptiles were the first true land
animals.
oThey have shell-covered eggs that can
be laid on land.
oThe elimination of the water-dwelling
stage is an important evolutionary
change.
Reptiles Dominate
oWith the perfection of the shelled egg,
reptiles became the dominant land animals.
oThis dominance continued for more than
160 million years.
oDinosaurs were some of the most
awesome reptiles.
oCarnivores, Herbivores.
oLarge, Small
oLand, Sea, Air
oAt the end of the Mesozoic, many reptile groups became extinct. Only a
few types survived.
oTurtles, snakes, crocodiles, lizards, etc.
oScientists believe this extinction occurred due to a large meteorite
that collided with Earth. Causing huge quantities of dust that blocked
the sun.
oThe smaller species probably survived because they must have
required a smaller amount of food.
Cenozoic Era
IV. Cenozoic Era: Age of Mammals
A. Cenozoic North America
B. Cenozoic Life
1. Mammals Replace Retiles
2. Large Mammals and Extinction
Cenozoic Era
oThe Cenozoic Era is the ‘era of recent life’. This involves the past 65 million years of
Earth’s History. This era is the time of mammals, including humans.
oDuring this time span the physical landscapes and life forms of our modern world
came into being.
oThe Cenozoic Era represents a much smaller fraction of geologic time than either
the Paleozoic or Mesozoic.
oThe rock formations during this time are more widespread and less disturbed than
those of any other preceding time.
oThe Cenozoic Era is divided into two periods of unequal duration: the Tertiary
period and the Quaternary Period.
Cenozoic North America
oMost of North America was above sea level throughout the Cenozoic Era.
oPlate interactions during the Cenozoic caused many events of mountain
building, volcanism, and earthquakes in the West.
Cenozoic Life
oMammals replaced reptiles as the dominant land animals in the Cenozoic.
oCenozoic is often called the “age of mammals”. This is because land animals
came to dominate land life. It is sometimes referred to the ‘age of flowering
plants’
oAngiosperms are flowering plants with covered seeds. They replaced
gymnosperms as the dominant land plants.
oMarine invertebrates took on a modern look.
oDevelopment of flowering plants strongly influenced evolution of both birds and
mammals.
oDue to the emergence of grassy fields, grazing animals became established.
Mammals Replace Reptiles
oOnce dinosaurs became extinct, mammals became the dominant land animals.
oThis transition is a major example in the fossil record of the replacement of one
large group by another.
oMammals are very distinct from reptiles.
oMammals are born alive rather than in a shelled-egg
oThey maintain a steady body temperature
o“warm-blooded” Therefore, can survive in the cold
oSearch for food during all seasons and at all times of the day
oDeveloped insulating body hair and more efficient heart and lungs
oThe mammals adaptions allow them to lead more active lives than reptiles.
oThe Cenozoic mammals diversified rapidly.
oMany forms evolved from small primitive mammals with short legs, flat
five-toed feet and small brains
oTheir development and specialization took four principal directions
oIncrease in size
oIncrease in brain capacity
oSpecialization of teeth to accommodate diet
oSpecialization of limbs to better equip life in a particular environment
Large Mammals and Extinction
oSome groups of mammals became very large
oMany large forms of mammals were common as recently as 11,000 years ago.
oA wave of Pleistocene extinctions rapidly eliminated these larger animals from
the landscape.
oScientists believe that early humans hurried the decline of these mammals by
selectively hunting.
oThis is because these animals have already survived major glacial advances and
interglacial periods. It is difficult to say that climate changes caused the
extinctions.