1. Earth’s History
Chapter 13

2. Earth’s History – Chapter 13
I. Precambrian Time: Vast and Puzzling A. Precambrian History Precambrian Rocks Earth’s Atmosphere Evolves Precambrian Fossils II. Paleozoic Era: Life Explodes A. Early Paleozoic Early Paleozoic History Early Paleozoic Life B. Late Paleozoic Late Paleozoic History Late Paleozoic Life C. The Great Paleozoic Extinction III. Mesozoic Era: Age of Reptiles A. Mesozoic Era Mesozoic History Mesozoic Life The Shelled Egg Reptiles Dominate IV. Cenozoic Era: Age of Mammals A. Cenozoic North America B. Cenozoic Life Mammals Replace Retiles Large Mammals and Extinction

3. Precambrian History
The 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.
The Precambrian comprises about 88% of the Geologic Time Scale.
Most Precambrian rocks do not contain fossils. This makes correlating rocks difficult.
Most rocks during this age are metamorphosed and deformed, extremely eroded, and hidden by overlaying strata.

5. Precambrian Rocks
The lack of Precambrian Rock illustrates the law of superposition.
Precambrian Rocks are buried from view underneath more recent rocks.
Precambrian Rocks only show through the surface where younger strata are extensively eroded.
Examples: The Grand Canyon and Mountain Ranges
Large core areas of Precambrian Rocks dominate the surface of some continents, mostly deformed metamorphic rocks.

6. Shields are large, relatively flat expanses of ancient metamorphic rock within the stable continental interior.
Much of what we know about Precambrian rocks comes from ores mined from shields.
The mining of iron, nickel, gold, silver, copper, chromium, uranium and diamonds have provided rock samples of Precambrian time.

7. Earth’s Atmosphere Evolves
Early in Earth’s History, the high velocity impact of nebular debris caused the outer shell of our planet to melt.
Earth then slowly cooled and the surface solidified into the crust and gases were dissolved.
Earth’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.
As Earth continued to cool, the water vapor condensed to form clouds and rain began.

8. The first life forms on Earth did not need oxygen.
Primitive organisms evolved that used photosynthesis and released oxygen.
These organisms influenced Earth’s atmosphere- they used carbon dioxide and produced oxygen.
Slowly, the oxygen content increased on Earth
Oxygen began to accumulate in the atmosphere about 2.5 billion years ago.

9. Precambrian Fossils
The most common Precambrian fossils are stromatolites.
Stromatolites are distinctively layered mounds or columns of calcium carbonate.
They are NOT the remains of actual organisms but are material deposited by algae.
Stromatolites are indirect evidence of algae because they closely resemble similar deposits made by modern algae.
Stromatolites were commonly found in the middle Precambrian time.

11. Many ancient fossils are preserved in chert.
Chert is hard, dense chemical sedimentary rock.
Chert must be sliced very thin and studied under a powerful microscope.
These fossils are the most primitive organisms, called prokaryotes.
More advanced organisms called eukaryotes evolved later.
The development of eukaryotes has dramatically increased the rate of revolutionary change.
We start to see animal fossils in the late Precambrian in the form on trace fossils.

12. Earth’s History Section 2
II. Paleozoic Era: Life Explodes A. Early Paleozoic Early Paleozoic History Early Paleozoic Life B. Late Paleozoic Late Paleozoic History Late Paleozoic Life C. The Great Paleozoic Extinction

13. Paleozoic Era: Life Explodes
Following the long Precambrian, the most recent 540 million years of Earth’s history are divided into three era: Paleozoic, Mesozoic and Cenozoic.
The Paleozoic Era encompasses about 292 million years and is the longest of the three eras.
The Paleozoic Era contains many more diverse fossils due to the emergence of life forms with hard parts (shells, scales, bones or teeth)
This allowed for a far more detailed section for the remaining 1/8 of the Geologic Time Scale.

14. 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

15. Early Paleozoic Early Paleozoic consists of 123 million years.
Including Cambrian, Ordovician and Silurian periods
During the Cambrian, Ordovician and Silurian periods, the southern continent of Gondwana encompassed five continents
South America, Africa, Australia, Antarctica and parts of Asia
North 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.
During the Paleozoic Era North America was a land with no living things, plants or animals.

16. Early Paleozoic Life
Life in early Paleozoic time was restricted to the seas.
Vertebrates had not yet evolved, so life consisted of several invertebrate groups.
The Cambrian period was the golden period of trilobites.
More than 600 types of these mud-burrowing scavengers flourished world-wide.

17. Ordovician Period
In the Ordovician period, brachiopods outnumbered the trilobites. Brachiopods are among the most widespread Paleozoic fossils
The Ordovician period also marked the appearance of cephalopods- mobile and highly developed mollusks that became the major predators.
Squid and octopus are descendents of these early cephalopods.
Cephalopods were the first truly large organisms on Earth.

18. Cambrian Period
The beginning of the Cambrian period marks an important event in the animal evolution.
Organisms appeared that secreted material that formed hard parts, such as shells
Hard parts clearly served many useful purposes and aided adaptions to new ways of life.
The development of exoskeletons began.

19. Late Paleozoic The late Paleozoic consists of four periods.
Devonian, Mississippian, Pennsylvanian and Permian
This span was about 160 million years.
Tectonic forces reorganized Earth’s landmasses during this time, creating the supercontinent Pangea.

20. Late Paleozoic History
North America and Africa collided, the narrow sea between the two began to close.
Strong forces of compression deformed the rocks to produce the Appalachian Mountains of eastern North America.
By the Permian period, a newly formed landmass was created by the collision of western Asia and the Siberian landmass. This landmass is called Laurasia.
By the Pennsylvanian period, Laurasia formed and Gondwana moved north. The Gondwana collided with Laurasia forming a mountain belt in Europe.
By the end of the Paleozoic Era, all the continents had fused together into the supercontinent Pangea.

21. Late Paleozoic Life
Some 400 million years ago, plants that had adapted to survive at the water’s edge began to move inland, becoming land plants.
The earliest plants were leafless vertical spikes about the size of an index finger.
By the end of the Devonian period, 40 million years later, the fossil record indicated the existence of forests with trees tens of meters high.

22. In the oceans, armor-plated fish evolved during the Ordovician period adapted in the Devonian period.
Other 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’
By the Pennsylvanian Period, large tropical swaps extended across North America, Europe and Siberia. Trees are growing. Coal deposits originated. Amphibians evolved quickly.

23. The Great Paleozoic Extinction
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.
Close to the Permian, 75 percent of the amphibian families had disappeared. Plants had declines in number and variety.
Much of marine life did not adapt and survive. 80%-95% of marine life disappeared.
Many marine invertebrates that were dominant during the Paleozoic Era including trilobites, coral and brachiopods could not adapt.

24. The late Paleozoic extinction was the greatest of five mass extinctions to occur over the past 500 million year.
However, survivors forming new biological communities
This mass extinction allowed life on Earth to flourish.
The cause of the Paleozoic extinction is uncertain, but it is clear that without it a very different population of organisms would exist today.

25. Section 3- Mesozoic Era
III. Mesozoic Era: Age of Reptiles A. Mesozoic Era Mesozoic History Mesozoic Life The Shelled Egg Reptiles Dominate

26. Mesozoic Era
The Mesozoic Era spanned about million years and is divided into three periods. Triassic, Jurassic and Cretaceous.
The Mesozoic Era marked the beginning of the breakup of the supercontinent Pangea.
On land, dinosaurs became dominant and were unchallenged for over 100 million years.

27. Mesozoic History
The Mesozoic Era began with much of the land above sea level. Very few marine fossils were found during the Triassic period.
In the beginning of the Cretaceous Period, the shallow seas became swamp-like areas where coal deposits formed becoming important to the United States now.
Following the beginning of Pangea’s breakup, a rift developed between what is now the United States and Africa. This rift becomes the Atlantic Ocean.
Pangea took 200 million years to breakup into what the continents are now.

28. Mesozoic Life
Life forms that were present during the Mesozoic Period were the only life forms that survived the Paleozoic extinction.
Gymnosperms, 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.
Gymnosperms quickly became the dominant plants of the Mesozoic.
Consisted of: Cycads, Conifers and Ginkgoes.

29. The Shelled Egg
Reptiles readily adapted to the drier Mesozoic environment.
Reptiles were the first true land animals.
They have shell-covered eggs that can be laid on land.
The elimination of the water-dwelling stage is an important evolutionary change.

30. Reptiles Dominate
With the perfection of the shelled egg, reptiles became the dominant land animals.
This dominance continued for more than million years.
Dinosaurs were some of the most awesome reptiles.
Carnivores, Herbivores.
Large, Small
Land, Sea, Air

31. At the end of the Mesozoic, many reptile groups became extinct
At the end of the Mesozoic, many reptile groups became extinct. Only a few types survived.
Turtles, snakes, crocodiles, lizards, etc.
Scientists believe this extinction occurred due to a large meteorite that collided with Earth. Causing huge quantities of dust that blocked the sun.
The smaller species probably survived because they must have required a smaller amount of food.

32. Cenozoic Era
IV. Cenozoic Era: Age of Mammals A. Cenozoic North America B. Cenozoic Life Mammals Replace Retiles Large Mammals and Extinction

33. Cenozoic Era
The 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.
During this time span the physical landscapes and life forms of our modern world came into being.
The Cenozoic Era represents a much smaller fraction of geologic time than either the Paleozoic or Mesozoic.
The rock formations during this time are more widespread and less disturbed than those of any other preceding time.
The Cenozoic Era is divided into two periods of unequal duration: the Tertiary period and the Quaternary Period.

34. Cenozoic North America
Most of North America was above sea level throughout the Cenozoic Era.
Plate interactions during the Cenozoic caused many events of mountain building, volcanism, and earthquakes in the West.

35. Cenozoic Life
Mammals replaced reptiles as the dominant land animals in the Cenozoic.
Cenozoic 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’
Angiosperms are flowering plants with covered seeds. They replaced gymnosperms as the dominant land plants.
Marine invertebrates took on a modern look.
Development of flowering plants strongly influenced evolution of both birds and mammals.
Due to the emergence of grassy fields, grazing animals became established.

36. Mammals Replace Reptiles
Once dinosaurs became extinct, mammals became the dominant land animals.
This transition is a major example in the fossil record of the replacement of one large group by another.
Mammals are very distinct from reptiles.
Mammals are born alive rather than in a shelled-egg
They maintain a steady body temperature
“warm-blooded” Therefore, can survive in the cold
Search for food during all seasons and at all times of the day
Developed insulating body hair and more efficient heart and lungs
The mammals adaptions allow them to lead more active lives than reptiles.

37. The Cenozoic mammals diversified rapidly.
Many forms evolved from small primitive mammals with short legs, flat five-toed feet and small brains
Their development and specialization took four principal directions
Increase in size
Increase in brain capacity
Specialization of teeth to accommodate diet
Specialization of limbs to better equip life in a particular environment

38. Large Mammals and Extinction
Some groups of mammals became very large
Many large forms of mammals were common as recently as 11,000 years ago.
A wave of Pleistocene extinctions rapidly eliminated these larger animals from the landscape.
Scientists believe that early humans hurried the decline of these mammals by selectively hunting.
This is because these animals have already survived major glacial advances and interglacial periods. It is difficult to say that climate changes caused the extinctions.