A Trip Through Geologic Time

1
A Trip Through Geologic Time

• Fossils
• Relative Age
• Radioactive Dating
• The Geologic Time Scale
• Earths History

2
Fossils

• How do fossils form?
• What are the different types of fossils?
• What do fossils tell about how organisms have
  changed over time?

3
The Burgess Shale

• In 1909, Charles Walcott was exploring at an
  altitude of 7450 feet in the Canadian Rockies and
  discovered a very rich collection of fossils in a
  layer of shale. This rock outcrop became known as
  the Burgess Shale.

4
Burgess Shale - Hallucigenia

• Hallucigenia was a strange little bottom-dwelling
  creature with leg-like processes and strongly
  developed dorsal spines. This animal was about 2
  cm in length.

5
Burgess Shale - Anomalocaris

• Anomalocaris was the most fearsome predator of
  the Burgess fauna. Up to 60 cm long, it used
  arm-like processes to capture prey, which were
  eaten with a mouth equipped with a circle of
  tooth-like, sharpened plates.

6
The Burgess Shale

• These were sea creatures unlike anything found on
  Earth.
• How did they get there?
• What is the story behind this record in the
  rocks?

7
Fossil Formation

• Death in a water environment
• Sedimentation
• Mineralization
• Uplift

8
1-Death in water environment

• The first step of fossil formation an animal or
  plant must die in water or near enough to fall in
  shortly after death. The water insulates the
  remains from many of the elements that contribute
  to decomposition.

9
2-Sedimentation

• As time passes sediments bury the exoskeleton.
  The faster this happens the more likely
  fossilization will occur. Land and mud slides
  definitely help. River deltas are also good for
  quick accumulation of sediments.

10
3-Mineralization

• As the sediments continue to pile on, the lower
  layers become compacted by the weight of the
  layers on top. Over time, this pressure turns the
  sediments into rock.

11
3-Mineralization

• If mineral-rich water percolates down through the
  sediments, the fossil formation process has an
  even better chance of preserving our ancient
  animal. Some of the minerals stick to the
  particles of sediment, effectively gluing them
  together into a solid mass.

12
3-Mineralization

• Over the course of millions of years they
  dissolve away the outer shell, sometimes
  replacing the molecules of exoskeleton with
  molecules of calcite or other minerals.

13
4-Uplift

• As the continental plates move around the earth,
  crashing into each other, mountains are formed.
  Former sea floors are lifted up and become dry
  land.

14
Types of Fossils

• Molds and Casts
• Carbon Films
• Trace Fossils
• Preserved Remains

15
Mold

• Hollow impression in a rock in the shape of an
  organism or part of an organism.
• A mold forms when the hard part of the organism
  is buried in sediment and then dissolves.

16
Cast Fossil

• A cast is a copy of the shape of an organism.
• Casts occur when the minerals in an organism are
  replaced by minerals.

17
Carbon Film Fossils

• Heat and pressure can remove all volatile remains
  of an organism, leaving just a thin film of
  carbon on a rock.

18
Trace Fossils
Footprints
Burrows
Coprolites
19
Relative Age of Rocks

• How do geologists determine the relative age of
  rocks?
• How are index fossils useful for geologists?

20
Principles of Geology

• James Hutton 1726-1797 stated first modern theory
  of geology
• Hutton identified most of the processes that
  shape rocks in the Earths crust.

21
Huttons Unconformity

• Hutton was puzzled by a very interesting rock
  formation at Siccar Point near his home in
  England
• This is now known as Huttons Unconformity

22
Huttons New Story of Geology

• The earth is shaped by erosion, deposition and
  uplift acting over very long periods of time.
• Geology Principles allow us to read geological
  formations to infer their relative ages and
  history.
• Fossils found in rock layers provide additional
  information about age.

23
Principle of Uniformitarianism

• Geologic processes observed in operation that
  modify the Earth's crust at present have worked
  in much the same way over geologic time.
• The present is the key to the past.

24
Principle of Original Horizontality

• The deposition of sediments occurs as essentially
  horizontal beds
• Any slope in sedimentary layers is the result of
  folding, faulting or uplift.

25
Principle of Superposition

• States that a sedimentary rock layer in a
  tectonically undisturbed sequence is younger than
  the one beneath it and older than the one above
  it.

26
Principle of Intrusive Relationships

• When an igneous intrusion cuts across a formation
  of sedimentary rock, it can be determined that
  the igneous intrusion is younger than the
  sedimentary rock.

27
Unconformities - Erosion

• Unconformities occur when sedimentary layers are
  uplifted and eroded.
• This produces a gap in the geological record.

28
Unconformity in the Grand Canyon
29
Quiz Which is older?

• F or G?
• E or L?
• A or D?
• L or K?
• J or L?
• J or K?

30
Principle of Faunal Succession

• Sedimentary rock layers contain fossilized flora
  (plants) and fauna (animals), and that these
  fossils succeed each other vertically in a
  specific, reliable order that can be identified
  over wide horizontal distances.
• Index fossils can be used to establish relative
  ages of rocks.

31
Some Index Fossils
32
Characteristics of Index Fossils

• Worldwide found everywhere on Earth
• Shelled Animal very likely to have been
  fossilized
• Only lived during a specific period and are not
  found outside that period.

33
Index fossils allow correlation of rock layers in
different areas
34
Fossils allow correlation in spite of
unconformities.
35
The Geologic Column

• Geologic principles and index fossils allow
  worldwide correlation.
• The names of different layers have been
  standardized into a worldwide geologic column.
• The layers represent different times in the
  Earths history based on relative ages.

36
The Geologic Column
37
Radiometric Dating

• What happens during radioactive decay?
• What can be learned from radioactive dating?
• How did scientists determine the age of the earth?

38
Radioactivity

• In 1896, Henri Becquerel laid some uranium salts
  on photo film.
• When he developed the film, it showed an exposed
  area from the uranium

39
Types of Radioactive Decay

• Alpha He nucleus not very penetrating.
• Beta electron more penetrating
• Gamma EM radiation very penetrating

40
Radioactive Decay Alpha

• Here Am-241 (parent nucleus) decays into Np-237
  (daughter nucleus).
• This produces an alpha particle (Helium nucleus)
  and much energy.

41
Radioactive Decay Beta

• Here, Hydrogen-3 (parent nucleus) decays into
  Helium-3 (daughter nuclesu) and an electron
• Beta radiation can emit either an electron (-
  charge) or positron ( charge).

42
Radioactive Decay Gamma

• Gamma rays are high-energy electromagnetic
  radiation, similar to light.
• They may be given off from a number of different
  processes involving the nucleus
• They have no mass, but may be able to penetrate
  deeply into matter. They require shielding of a
  few feet of dirt or a few inches of lead shielding

43
Radioactive Decay

• Different combinations of protons and neutrons
  are called nuclides.
• Some nuclides are very unstable and explode to
  form other nuclides in a process called
  radioactive decay.
• The more unstable the nuclide is, the more
  quickly it will explode.

44
Radioactive Decay Series U238
45
Half-Life

• The half-life of a nuclide is the time required
  for half of the atoms of the parent nucleus to
  decay.
• The shorter the half-life, the more unstable is
  the nuclide.

46
Radioactive Decay Rate

• The rate of radiation decreases with time in a
  predictable way.
• The half-life of a nuclide is not affected by
  heat, pressure, chemical conditions, gravity or
  magnetism.
• Rutherford and Soddy realized that radioactive
  decay could be used as a clock to date rocks.

47
Setting of the Radioactive Clock

• Radiometric dating can only be performed on
  igneous rocks.
• When the melted rock solidifies as it cools, it
  locks its atoms into place in its crystal
  structure.
• As atoms in it decay, they remain in place in the
  crystal allowing labs to determine their ratio.

48
Isotope Ratios and Age of Rocks
49
Commonly used dating isotopes
50
The Age of the Earth - Estimates
51
The Age of the Earth - Estimates
52
Geologic Time

• Why is the geologic time scale used to show
  Earths history?
• What are the different units of the geologic time
  scale?

53
Deep Time
Consider the earth's history as the old measure
of the English yard, the distance from the King's
nose to the tip of his outstretched hand. One
stroke of a nail file on his middle finger erases
human history. John McPhee

• Geologic Time or Deep Time is almost
  unimaginably long.

54
What events divide geologic time?

• Mass extinctions abrupt changes in the fossil
  record
• Catastrophes Asteroid / Comet impacts,
  supervolcanos
• Climate change rapid switching between warmer
  and colder climates
• Tectonic changes Continental movement across
  the globe

55
Geologic Time Divisions

• Eons Longest units of time. Hadean, Archean,
  Proterozoic...
• Eras Divide eons. Paleozoic, Mesozoic,
  Cenozoic...
• Periods Divide ErasTriassic, Jurassic,
  Cretaceous, Quaternary...
• Epochs or Series Divide Periods Holocene,
  Pleistocene, Pliocene, Eocene, Paleocene...

56
Geologic Time Divisions
57

• Age of the earth 2,827 miles about the
  distance from Boston to Los Angeles
• Lucy lived 2 million years 1.2 miles
• Agriculture invented 10 meters, or about the
  length of the classroom
• United States Exists 23.5 cm or 10 inches
• Your life span so far 1.5 cm or about the width
  of your thumb

58
Fossil Record of Biological Evolution
More Complex Life

• As millions of years of earth history pass, life
  gradually develops and becomes more complex as
  time passes.

Very Simple Life
59
Fossil Record of Biological Evolution

• Over time, life has steadily grown more and more
  complex.
• Precambrian fossils show only the simplist life
  forms bacteria in the form of Stromatolites.

60
Fossil Record of Biological Evolution

• 500 million years ago early life blooms.
• Early Paleozoic Era fossils include no fish,
  reptiles, birds or mammals only simple marine
  life.

61
Fossil Record of Biological Evolution

• 360 million years ago age of fish.
• Devonian age showed early forms of fish. No
  fossils of reptiles, birds or mammals are present.

62
Fossil Record of Biological Evolution

• 245 million years ago near the end of the
  Paleozoic Era.
• Permian Period, complex life was found on land
  including early reptiles. No fossils of birds or
  mammals yet.

63
Plate Tectonics

• Continental land masses have not remained fixed
  in one place over geological time, but have
  continuously moved in relation to each other.

64
Evidence for Plate TectonicsTopographic Fit

• The edges of continents such as South America and
  Africa appear to match. This apparent jigsaw-like
  fit is no coincidence.

65
Evidence for Plate Tectonics Tectonic Fit

• The positions and ages of tectonic features which
  occur on the various continental landmasses seem
  to join up. This is best seen in the cratons of
  Africa and South America, and in the mountain
  belts of northern Africa and southern Europe.

66
Evidence for Plate Tectonics Stratigraphic Fit

• Continents which were once part of the same
  landmass will show similar rock sequences along
  their margins up until the time when they split
  apart.

67
Evidence for Plate Tectonics Fossil Correlation

• Fossils contained within stratigraphic sequences
  which are now located on different continents can
  indicate that the two landmasses were once
  joined.

68
Earths History

• What were the major events in Earths geologic
  history?
• What were the major events in the development of
  life on Earth?

69
Earth Formation

• The solar system is thought to have condensed
  from a nebula similar to the M16 Pillars of
  Creation shown here.
• Heavy elements had to be formed inside supernova
  stars that exploded before the cloud condensed.

70
Nebular Theory

• Over millions of years, the very thin nebula
  cloud condenses into the sun and planets.
• Gravity provides the force that pulls the matter
  together, while the system keeps revolving
  because of conservation of angular momentum.

71
Collision Theory of the Moon

• The most accepted theory of the moon is that it
  was the result of a collision between the earth
  and a Mars-sized object during the Hadeon eon
  very early in the Earths history.
• This collision theory also explains the Earths
  tilt.

72
Precambrian - Hadean Eon

• The Hadean eon (4.6M to 3.8M) saw a hot earth
  with much water vapor and carbon dioxide in the
  atmosphere.
• The surface temperature was around 230F
• Very little surface from the Hadean period exists
  on earth today mainly some zircon crystals and
  a very few rocks.

73
Precambrian - Achean Eon

• The Achean eon (3.8M to 2.5M) saw much volcanism
  at first, slowing later.
• Continents were small at first, gradually growing
  as the earth cooled at the end of the eon.
• Blue-green algae in the form of stromatolites
  began to produce free oxygen.

74
Precambrian Proterozoic Eon

• The Proterozoic Eon (2.5M to 550K) saw the
  evolution of the first multicellular life.
• The red-bands of iron deposits were the result of
  a steady increase in free oxygen in the
  atmosphere.

75
Precambrian Glaciations

• Late in the Proterozoic, all the continents
  combined to form the supercontinent Rodinia.
• This disrupted the ocean currents and resulted in
  a worldwide glaciation called Snowball Earth
• Snowball earth nearly extinguished all life on
  Earth.

76
Paleozoic Era Cambrian

• 544-505 my bce
• O2-12.5
• CO2-4500 ppm
• Temp 21C
• 30-gt90 m

• Ancient continents Laurentia and Baltica near the
  equator, and Gondwanaland near the south pole.
• Shallow seas cover much of the land

77
Paleozoic Era Cambrian Period

• Flora No land plants. A scum of fungi and algae
  covered the land.

• Animals Most invertebrate phyla evolve rapidly
  during the Cambrian explosion a period of 10-30
  million years.
• Trilobites, sponges, pikaia (chordate) clams
  lived during this period.

78
Paleozoic Era Ordovician

• 505-438 my bce
• O2-13.5
• CO2-4200 ppm
• Temp 16C
• 180m

• Warm shallow seas cover much of the Earth.
• Ice cap covers present day North America
• Cambrian explosion In a short time, all but one
  of the modern phyla appeared on earth.

79
Paleozoic Era Ordovician Period

• Plants Land plants included only liverworts and
  mosses.

• Marine animals increased four-fold. Invertebrates
  dominate the ocean.
• Cephalopods (octopi, squids) brachiopods,
  crinoids, and jawless fish evolved during this
  time.

80
Paleozoic Era Silurian Period

• 438-408 my bce
• O2-14
• CO2-4500 ppm
• Temp 17C
• 180m

• Early continents Laurasia and Baltica collide
  building mountains.
• Silurian marks the beginning of a long warm
  greenhouse climate phase, producing violent
  storms.

81
Paleozoic Era Silurian Period

• Plants Moss forests grow along streams and
  lakes.
• First fossils of vascular plants on land.

• Coral reefs and jawed fish evolve.
• Eurypterids (sea scorpions) terrorize the seas.
• Insects and spiders first appear in the fossil
  record.

82
Paleozoic Era Devonian

• 408-360 my bce
• O2-15
• CO2-2200 ppm
• Temp 20C
• 180-gt120 m

• Seas rise and fall over present day North
  America.
• Devonian was a warm period with very high sea
  levels and shallow seas covering much of the land.

83
Paleozoic Era Devonian Period

• O2-15
• CO2-2200 ppm
• Temp 20C
• 180-gt120 m

• Seas rise and fall over present day North
  America.
• Devonian was a warm period with very high sea
  levels and shallow seas covering much of the land.

84
Paleozoic Era Carboniferous Period

• O2-32.5
• CO2-800 ppm
• Temp 14C
• 120-gt0 m

• Appalachian mountains begin to form
• North America and Northern Europe are in warm,
  tropical regions
• South America and Africa are in polar regions and
  are glaciated.

85
Paleozoic Era Carboniferous Period

• Forests grow in swampy areas.
• Great swamp forests cover tropics will become
  todays coal.

• First true reptiles evolve
• Insects are abundant and first winged insects
  appear.

86
Paleozoic Era Permian Period

• 286-245 my bce
• O2-23
• CO2-900 ppm
• Temp 16C
• 60m-gt-20m

• Pangaea forms, large tropical deserts and
  southern glaciation
• Permian ended in the great dying, the most
  complete mass extinction known

87
Paleozoic Era Permian Period

• Primitive cockroaches and dragonflies thrived
• Swamp-type vegetation was replaced by seed ferns
  and conifers
• First ginkgos and cycads appear in this period

• Mammal-like Pelycosaurs (sail backs) were a
  common tetrapod
• Diapsids are unimportant in the Permian, but
  would later evolve into dinosaurs

88
Great Dying Event

• Occurred at the end of the Permian Period (End P
  at right)
• As many as 70 of all species and perhaps 99.5
  of all individuals died

• Possible causes Siberian traps flood basalt or
  venting of hydrogen sulfide gas, or climate
  change triggered by frozen methane reservoirs.
• Other candidates for cause include a nearby
  supernova and an impact crater in Antarctica.

89
Mesozoic Era Triassic Period

• 245-208 my bce
• O2-16
• CO2-1750 ppm
• Temp 17C

• Almost all the Earths land mass was concentrated
  in the supercontinent Pangaea.
• Climate was hot and dry and even the poles were
  temperate.

90
Mesozoic Era Triassic Period

• Gingkos and cycads were common
• Seed plants began their domination
• First mammals

• Crurotarsi groups thrive, including crocodiles.
• Onithodira (bird-necked) groups include
  pterosaurs (flying dinosaurs)
• Carnivores cynognathus (dog-head) and cynodonts
  (dog-tooth) spread world-wide

91
Mesozoic Era Jurassic Period

• 208-144 my bce
• O2-26
• CO2-1950 ppm
• Temp 16.5C

• Pangaea breaks apart into Gondwana and Laurasia.
• Age of reptiles continues

92
Mesozoic Era Jurassic Period

• Warm, lush forests conifers thrive
• Ginkgos and ferns were common
• First birds evolved

• Ichthyosaurs and pleosaurs dominate the seas and
  pterosaurs flew in skies.
• Giant Saurpods thrived, preyed upon by large
  theropods

93
Mesozoic Era Cretaceous Period

• 144-65 my bce
• O2-30
• CO2-1700 ppm
• Temp 18C

• Gondwanaland and Laurasia split as modern
  continents form
• Widespread volcanism results in warming from
  increased carbon dioxide

94
Mesozoic Era Cretaceous Period

• First flowering plants
• Dinosaurs dominate
• First snakes appear

• Sea life included modern sharks, ichthyosaurs,
  and plesiosaurs
• Many species of dinosaurs flourished including
  T-Rex

95
K-T Extinction Event

• Caused by a mountain-sized asteroid hitting the
  Yucatan Peninsula
• Led to the extinction of most dinosaurs
• Led to radiative evolution of mammals

• Simultaneous with impact was the Deccan traps, a
  flood basalt event in India
• Impact may have produced massive dust clouds and
  a worldwide nuclear-winter event.

96
Cenozoic Era Tertiary Period

• 65-1.6 my bce
• O2-25-gt21
• CO2-1700 ppm
• Temp 22-gt12C

• The Americas move west away from Africa and
  Europe, and join with a land-bridge
• New circulation patterns in the later Cenozoic
  result in regular ice ages
• Worldwide temperatures fall along with carbon
  dioxide percentages

97
Cenozoic Era Tertiary Period

• Flowering plants thrive
• First grasses evolve
• Modern mammals classes evolve

• Horses, elephants, bears, rodents and primates
  appear
• Mammals return to the seas and evolve into whales
  and dolphins.
• Reptiles diversify into modern crocodilians,
  snakes and turtles.
• Birds radiate into modern bird groups.

98
Cenozoic EraExtinct Mammals
Killer Pigs! Entelodon from the Late Eocene and
Early Oligocene of Asia
Andrewsarchus from the Paleogene
99
Cenozoic Era Tertiary Period

• 65-1.6 my bce
• O2-25-gt21
• CO2-1700 ppm
• Temp 22-gt12C

• The Americas move west away from Africa and
  Europe, and join with a land-bridge
• New circulation patterns in the later Cenozoic
  result in regular ice ages
• Worldwide temperatures fall along with carbon
  dioxide percentages

100
Cenozoic Era Quaternary Period

• Mammals, flowering plants and insects dominate
• A dozen or more ice ages occurred at intervals of
  around 100,000 years.

• Algae, coral, mollusks, fish and mammals thrive
  in the ocean. Insects, birds, and many types of
  mammals were common on land.
• A series of hominids lived during this time,
  eventually evolving to homo sapiens about 100,000
  to 200,000 years ago.
• Agriculture was invented 10,000 years ago leading
  to our current modern civilization.

101
Carbon Dioxide and Temperature