Chapter 12 Geologic Time Who is Stan Hatfield and Ken Pinzke.

Chapter 12 Geologic Time Who is Stan Hatfield and Ken Pinzke

12.1 Discovering Earth’s History
Studying Earth’s History 12.1 Discovering Earth’s History Three Main Ideas: The rock record provides evidence of geological events and life forms of the past. Processes observed on Earth in the present also acted in the past. Earth is very old and has changed over time.

A Brief History of Geology 12.1 Discovering Earth’s History Formulated by James Hutton, The principle of uniformitarianism simply states that physical, chemical and biological laws that operate today have also operated in the geologic past. Uniformitarianism means that the forces and processes that we observe today have been at work for a very long time To understand the past, we must first understand present-day processes and results.

Relative Dating—Key Principles 12.1 Discovering Earth’s History  Relative dating tells us the sequence in which events occurred, not how long ago they occurred.  Law of Superposition • The law of superposition states that in an undeformed sequence of sedimentary rocks, each bed is older than the one above it and younger than the one below it.

Ordering the Grand Canyon’s History
Makes no sense without caption in book

Relative Dating—Key Principles 12.1 Discovering Earth’s History  Principle of Original Horizontality • The principle of original horizontality means that layers of sediment are generally deposited in a horizontal position.

Disturbed Rock Layers Makes no sense without caption in book

Relative Dating—Key Principles 12.1 Discovering Earth’s History  Principle of Cross-Cutting Relationships • The principle of cross-cutting relationships states that when a fault cuts through rock layers, or when magma intrudes other rocks and crystallizes, we can assume that the fault or intrusion is younger than the rocks affected.  Inclusions • Inclusions are rocks contained within other rocks. • Rocks containing inclusions are younger than the inclusions they contain.

Applying Cross-Cutting Relationships

Formation of Inclusions

Relative Dating—Key Principles 12.1 Discovering Earth’s History  Unconformities • A surface that represents a break in the rock record. An unconformity represents a long period during which deposition stopped, erosion removed previously formed rocks, and then deposition resumed. • An angular unconformity indicates that during the pause in deposition, a period of deformation (folding or tilting) and erosion occurred.

Formation of an Angular Conformity

Relative Dating—Key Principles 12.1 Discovering Earth’s History  Unconformities • A nonconformity is when the erosional surface separates older metamorphic or intrusive igneous rocks from younger sedimentary rocks. • A disconformity is when two sedimentary rock layers are separated by an erosional surface.

A Record of Uplift, Erosion, and Deposition

Correlation of Rock Layers 12.1 Discovering Earth’s History Correlation is establishing the equivalence of rocks of similar age in different areas. Geologists correlate layers by noting position of a distinctive layer in a sequence of layers, and if they find the same layer in another location can infer that the same layer once covered both locations.

Correlation of Strata at Three Locations

12.2 Fossils: Evidence of Past Life
Fossil Formation 12.2 Fossils: Evidence of Past Life  Fossils are the remains or traces of prehistoric life preserved from the geologic past. They are important components of sediment and sedimentary rocks.  The type of fossil that is formed is determined by the conditions under which an organism died and how it was buried.

Fossil Types 12.2 Fossils: Evidence of Past Life Unaltered Fossils--Some remains of organisms—such as teeth, bones, and shells—may not have been altered, or may have changed hardly at all over time. .

Fossil Formation 12.2 Fossils: Evidence of Past Life  Altered Remains The remains of an organism are likely to be changed over time. • Petrified Fossils– Means “turned into stone” ; mineral rich water soaks into cavities and pores of the organism, minerals precipitate and fill the spaces. Molds and casts are another common type of fossil. Occur when an organism is buried in sediment and dissolved by the underground water. Molds reflect the shape and surface markings, Casts are created if the mold later becomes filled with minerals.

Fossil Formation 12.2 Fossils: Evidence of Past Life  Altered Remains continued: Carbonization or Carbon films is particularly effective in preserving leaves and delicate animals. It occurs when an organism is buried under fine sediment and over time the liquids and gases are squeezed out leaving behind a thin film of carbon. Often found in Black Shale. .

Fossil Formation 12.2 Fossils: Evidence of Past Life Preserved Remains: when all or part of the organism is saved with relatively little change Examples include: Mammoths in permafrost; insects in amber, Mastodons in the Le Brea Tar Pits in LA, CA •

Fossil Formation 12.2 Fossils: Evidence of Past Life  Indirect Evidence • Trace fossils are indirect evidence of prehistoric life. Includes tracks or footprints, worm burrows, coprolites (dung fossils), and gastroliths.  Conditions Favoring Preservation • Two conditions are important for preservation: rapid burial and the possession of hard parts.

Types of Fossilization

Fossils and the History of life 12.2 Fossils: Evidence of Past Life Two major scientific developments helped scientists explain fossil record: the principle of fossil succession and the theory of evolution. Fossil Succession: The principle of fossil succession states that fossil organisms succeed one another in a definite and determinable order. Therefore, any time period can be recognized by its fossil content

Fossils and Correlation 12.2 Fossils: Evidence of Past Life Theory of Evolution: Life forms change over time or evolved, by means of Natural Selection. Evidence for this adapation is found in the fossil record.  Index fossils are widespread geographically, are limited to a short span of geologic time, and occur in large numbers.

Fossil Formation 12.2 Fossils: Evidence of Past Life  Interpreting Environments • Fossils can also be used to interpret and describe ancient environments because animals evolve with adaptations suited to their environments. Examples: tooth type might indicate type of vegetation present, limestone on clam shells indicate shallow sea, coral fossils indicate a warm environment, etc.

Overlapping Ranges of Fossils

12.3 Dating with Radioactivity
Radioactivity is the spontaneous decay of certain unstable atomic nuclei. Radioactive isotopes result from the decay of an unstable parent element and continues until a nonradioactive isotope is formed. Example: Radioactive, unstable U-238 decays to form stable, nonradioactive Pb-206.

Common Types of Radioactive Decay

Half-Life 12.3 Dating with Radioactivity A half-life is the amount of time necessary for one-half of the nuclei in a sample to decay to a stable isotope. Example: if the half-life of an unstable isotope is 1 million years and 1/16th of the parent isotope remains, the amount indicates that 4 half-lives have passed and the sample must be 4 million years old.

The Half-Life Decay Curve

Radiometric Dating 12.3 Dating with Radioactivity  Each radioactive isotope has been decaying at a constant rate since the formation of the rocks in which it occurs. Radiometric dating is the procedure of calculating the absolute ages of rocks and minerals that contain radioactive isotopes. The ratio between the radioactive parent isotope and the daughter products is measured in the sample to be dated. The older the sample, the more daughter product it contains.

Radiometric Dating 12.3 Dating with Radioactivity  As a radioactive isotope decays, atoms of the daughter product are formed and accumulate.  An accurate radiometric date can be obtained only if the mineral remained in a closed system during the entire period since its formation.

Radioactive Isotopes Frequently Used in Radiometric Dating

Dating with Carbon-14 12.3 Dating with Radioactivity  Radiocarbon dating is the method for determining age by comparing the amount of carbon-14 to the amount of carbon-12 in a sample.  When an organism dies, the amount of carbon-14 it contains gradually decreases as it decays. By comparing the ratio of carbon-14 to carbon-12 in a sample, radiocarbon dates can be determined.

Importance of Radiometric Dating 12.3 Dating with Radioactivity  Radiometric dating has supported the ideas of James Hutton, Charles Darwin, and others who inferred that geologic time must be immense.

12.4 The Geologic Time Scale
The Geologic Time Scale is a timeline that divides the Earth’s history into units representing specific intervals of time. Structure of the Time Scale Eons represent the longest intervals of geologic time. Eons are divided into eras, Eras into periods, and periods into epochs. In general, breaks in the units represent a major geologic event and/or change in life form. 12.4 The Geologic Time Scale

Structure of the Time Scale 12.4 The Geologic Time Scale There are three eras within the Phanerozoic eon: the Paleozoic, which means “ancient life” the Mesozoic, which means “middle life” the Cenozoic, which means “recent life”

Structure of the Time Scale 12.4 The Geologic Time Scale  Each period within an era is characterized by somewhat less profound changes in life forms as compared with the changes that occur during an era.  The periods of the Cenozoic era are divided into still smaller units called epochs, during which even less profound changes in life forms occur.

Precambrian Time 12.4 The Geologic Time Scale  During Precambrian time, there were fewer life forms. These life forms are more difficult to identify and the rocks have been disturbed often.

The Geologic Time Scale

Chapter 13 Earth’s History Who is Stan Hatfield and Ken Pinzke

13.1 Precambrian Time: Vast and Puzzling
Precambrian History 13.1 Precambrian Time: Vast and Puzzling  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. .

Geologic Time Scale Makes no sense without caption in book

Earth forms as gravity pulled together dust, rock and Ice in space. Earth’s Atmosphere Evolves: 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. Later, primary plants evolved that used photosynthesis and released oxygen. Oxygen began to accumulate in the atmosphere about 2.5 billion years ago. The Oceans Form as the planets cool, water vapor forms clouds, rains begin, evaporate & cool surface, and torrential rains fill the oceans.

Precambrian Rocks 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

Remnants of Precambrian Rocks

 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 the material deposited by algae. • Many of these ancient fossils are preserved in chert—a hard dense chemical sedimentary rock.

During the Precambrian time the earliest life forms were: Prokaryotic (bacteria called cyanobacteria) Single celled Eukaryotes (Red and Green Algae) Multicellular Eukaryotes ( worms, jellyfish and coral-like organisms) 13.1 Precambrian Time: Vast and Puzzling

13.2 Paleozoic Era: Life Explodes
Early Paleozoic 13.2 Paleozoic Era: Life Explodes  Following the long Precambrian, the most recent 540 million years of Earth’s history are divided into three eras: Paleozoic, Mesozoic, and Cenozoic.

Early Paleozoic 13.2 Paleozoic Era: Life Explodes  Early Paleozoic History • During the Cambrian, Ordovician, and Silurian periods, the vast southern continent of Gondwana encompassed five continents (South America, Africa, Australia, Antarctica, and part of Asia).

Gondwana and the Continental Landmasses

Early Paleozoic 13.2 Paleozoic Era: Life Explodes  Early Paleozoic Life • Life in early Paleozoic time was restricted to the seas.

Cambrian Period Earth underwent dramatic changes Breakup of supercontinent Rodinia, new environments formed in shallow seas as Earth warmed after the Precambrian Ice Age Life changed as animals developed hard parts like shells, exoskeletons and backbones

Life in the Ordovician Period
Earth landmass Gondwana contained S. America, Africa, Australia, Antarctica and parts of Asia Life included early corals, Trilobites and brachiopods, & jawless fish in the oceans as well as the development of primitive plants called liverworts in moist areas on land Mass extinction due to an Ice Age and Volcanic explosions punctuated this Period. Makes no sense without caption in book

Paleozoic Era Silurian Period Devonian Period
A time of reef building and evolution of fish in the sea as well as plants and animals becoming widespread on land Vascular plants Arthropods Armor plated fish Jawed fishes and sharks evolve in seas, plants continue to colonize the land with insects, and later in the period amphibians evolved for life on land. Sharks, sponges Wingless insects and spiders Frogs and toads Club mosses and tree ferns In the Earth, Laurasia formed, colliding land masses to form the current day Appalachians

Paleozoic Era Permean Period
Carboniferous Period (often divided into Mississippian and Pennsylavnian Periods) Permean Period Earth’s continents Pangea in beginning, life continued as carboniferous until the greatest mass extinction to date at the end of the period. Life became more diverse: conifers became abundant, insects amphibians and reptiles evolved until the mass extinction killed 96% of all species. Development of the great “coal swamp forests” in wet, tropical regions, amphibians and insects became common, and the first reptiles evolved; Pangea began to form; sea levels rose and fell repeatedly forming limestone deposits from reef-building organism remains. Conifers lived in drier uplands

Late Paleozoic Plate Movements

The Great Paleozoic Extinction 13.2 Paleozoic Era: Life Explodes  The world’s climate became very seasonal, probably causing the dramatic extinction of many species.  The late Paleozoic extinction was the greatest of at least five mass extinctions to occur over the past 500 million years.

13.3 Mesozoic Era: Age of Reptiles
Can be divided into three periods Triassic—Pangea still existant; slow recovery from Permean extinction; reptiles evolved and 1st mammals appeared and gymnosperms flourished including the cycad and ginkgo; Pangea begins to break up at end Jurassic– Pangea continues to split; dinosaurs evolved and widely distributed, flying reptiles appeared; Climates were mild Cretaceous—Dinosaurs, birds, flowering plants and small mammals flourished until a mass extinction of the dinosaurs occurred at the end of the period. Makes no sense without caption in book

The Flying Reptile Pteranodon

Fossil Skull of an Extinct Crocodile

Cretaceous Extinction
Most scientists think a large meteorite collided with the Earth and caused the mass extinction at the end of the Cretaceous. Such a collision would have created enough dust to block out the sun for years causing death of plants and subsequently the plant-eating dinosaurs and then the meat-eating dinosaurs. This is supported by a layer if iridium, similar to that found in a stony meteorite, in an impact crater in the Yucatan Peninsula of Mexico that is of the appropriate age. Other hypotheses: that a huge volcanic eruption in India led to climate changes Disease may have been a factor since species were declining prior to mass extinction

13.4 Cenozoic Era: Age of Mammals
Cenozoic North America 13.4 Cenozoic Era: Age of Mammals  The Cenozoic era is divided into two periods of very unequal duration, the Tertiary period and the Quaternary period.  Plate interactions during the Cenozoic era caused many events of mountain building, volcanism, and earthquakes in the West and the total breakup of Pangea.

Cenozoic Life 13.4 Cenozoic Era: Age of Mammals  Mammals—animals that bear live young and maintain a steady body temperature— replaced reptiles as the dominant land animals in the Cenozoic era.  Angiosperms—flowering plants with covered seeds—replaced gymnosperms as the dominant land plants.

Cenozoic Life 13.4 Cenozoic Era: Age of Mammals  Mammals Replace Reptiles • Adaptations like being warm blooded, developing insulating body hair, and having more efficient heart and lungs allow mammals to lead more active lives than reptiles.

Fossils from La Brea Tar Pits

Cenozoic Life 13.4 Cenozoic Era: Age of Mammals  Large Mammals and Extinction • In North America, the mastodon and mammoth, both huge relatives of the elephant, became extinct. In addition, saber-toothed cats, giant beavers, large ground sloths, horses, camels, giant bison, and others died out on the North American continent. • The reason for this recent wave of extinctions puzzles scientists.

Chapter 12 Geologic Time Who is Stan Hatfield and Ken Pinzke.

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Chapter 12 Geologic Time Who is Stan Hatfield and Ken Pinzke.

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