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14.1 The record of life. CHAPTER 14 HISTORY OF THE EARTH. 14.1 The Record of Life… VOCABULARY. Isotope = atoms of the same element that have different numbers of neutrons. Fossil = evidence of an organism that lived long ago. Plate tectonics = the theory that explains how the continents move.

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14 1 the record of life vocabulary
14.1 The Record of Life… VOCABULARY
  • Isotope = atoms of the same element that have different numbers of neutrons.
  • Fossil = evidence of an organism that lived long ago.
  • Plate tectonics = the theory that explains how the continents move.
14 1 the record of life1
14.1 The Record of Life
  • Paleontologist
    • Scientists who study ancient life.
  • Early Earth:
  • Very hot
    • Caused by the energy created by the colliding meteorites.
    • This heated the Earth’s surface.
    • The compression of minerals and decay of radioactive materials heated its interior.
  • Volcanoes
    • Spewed lava and gas – releasing pressure from the Earth’s interior.
    • The gases helped to form the Earth’s early atmosphere.
14 1 the record of life2
14.1 The Record of Life
  • Earth’s Early Atmosphere…
    • Probably did not contain free oxygen, O2.
    • Water vapor, carbon dioxide and nitrogen were probably present.
    • We would not have been able to survive in early Earth’s atmosphere.
14 1 the record of life3
14.1 The Record of Life
  • Earth formed about 4.6 billion years ago.
  • Theory states that the Earth cooled enough for water vapor to condense.
  • This may have led to millions of years of rainstorms with lightning.
    • Depressions filled – oceans formed
  • First life on Earth about 3.5 billion years ago.
  • Scientists are not certain that Earth formed in this way.
  • It is one theory – no direct evidence of the earliest years of Earth’s history.
fossils clues to the past
Fossils… Clues to the Past
  • A fossil is evidence of an organism that lived long ago.
  • Scientists study fossils to learn about ancient species.
    • About 95% of the species that have existed are extinct – they no longer live on Earth.
  • Paleontologist = scientists who study ancient life.
    • Act like detectives…
    • They use fossils to understand events that happened long ago.
    • They use fossils to determine the kinds of organisms that lived during the past.
    • They also use fossils to try to learn about the organisms’ behaviors.
paleontologists detectives to the past
Paleontologists… Detectives to the Past

Examples of fossil evidence:

  • Fossil bones and teeth
    • Indicate the size of animals
    • How they moved
    • What they ate
  • Ancient climate and geography
    • Studying fossils helps scientists to learn about past climates and geography.
      • Finding a fossilized plant suggests that the past climate was mild.
    • The condition, position, & location of rocks and fossils, scientists can make deductions about the geography of past environments.
fossil formation
Fossil Formation…
  • Fossils form
    • When organisms are buried in mud, sand or clay soon after they die.
    • Particles are compressed over a long period of time and harden into a type of rock.
      • This rock is called sedimentary rock.
  • Fossils still form today at the bottom of lakes, streams, oceans.
fossil formation1
Fossil Formation…
  • Most fossils are found in sedimentary rocks.
    • Sedimentary rocks form at somewhat low temperatures and pressures.
      • This may prevent damage to the organism.
    • Sedimentary rocks form in horizontal layers, with younger layers closer to the surface.
    • Older fossils and rocks will be found in the deeper layers.
fossil formation2
Fossil Formation…
  • Fossils are not usually found in other types of rock for a number of reasons.
    • Metamorphic rocks form when heat, pressure, and chemical reactions change other rocks.
      • i.e., Marble / limestone; slate / shale…
    • These conditions often destroy any fossils that were present in the original sedimentary rock.
relative dating
Relative Dating…
  • Scientists use different methods to determine the age of fossils.
  • Figure 14.2
  • If rock layers have not been disturbed, the older layers will be below the younger layers…. Younger layers will be on top of older layers.
  • This also means that the fossils found in the lower layers are older than the fossils found in the layers closer to the surface.
  • Determines relative age (older than, younger than) and order of appearance of the species preserved as fossils in the layers.
radiometric dating
Radiometric Dating…
  • Relative dating does not determine the actual age in years of a fossil or rock.
  • Radiometric dating provides the specific age of rocks and fossils.
  • Scientists use radioactive isotopes in rocks to find the exact age in years.
  • Radioactive isotopes are atoms with unstable nuclei.
    • They break down over time.
    • They give off radiation.
    • A radioactive isotope forms a new isotope after it decays.
radiometric dating1
Radiometric Dating…
  • The half-life is the length of time needed for half of the atoms of the isotope to decay.
  • The ratio of radioactive isotope to the new isotope formed as it decays…
    • helps scientists to determine the approximate age of rocks.
  • Example of isotopes used in radiometric dating…
    • Potassium-40 decays to argon-40
radiometric dating2
Radiometric Dating…

For accurate, consistent values –

  • Many rock samples are used with a variety of testing methods.
  • Errors can happen if
    • the rock has been heated.
    • This will cause some of the radioactive isotopes to be lost or gained.
    • The age will be inaccurate in this case.
geologic time scale
Geologic Time Scale…
  • Calendar of Earth’s history.
  • Based on evidence from Earth’s rocks and fossils.
  • Figure 14.4
  • Divided into 4 large sections.
    • Precambrian
    • Paleozoic Era
    • Mesozoic Era
    • Cenozoic Era P P Me C
  • Era is a large division in the scale and equals a very long period of time.
    • Each era is subdivided into periods.
geologic time scale cont d
Geologic Time Scale, cont’d…
  • Divisions are distinguished by the organisms that lived during that time period.
  • Fossil record indicates that there were several mass extinctions that fall between time divisions.
    • Mass extinction = event that occurs when many organisms disappear from the fossil record nearly all at once.
precambrian
Precambrian
  • Accounts for about 87% of Earth’s history.
  • At the beginning of the Precambrian, about 3.4 billion years ago…
    • Unicellular organisms, bacteria, were the only life form.
    • About 2.1 billion years ago, eukaryotic organisms appeared.
    • At the end of the Precambrian, about 543 million years ago, multicellular eukaryotes, i.e., sponges and jellyfishes, diversified and filled the oceans.
paleozoic era
Paleozoic Era
  • Many more types of animals and plants present during this time.
  • Some were preserved in the fossil record.
  • The earliest part of the Paleozoic Era is the Cambrian Period.
    • Referred to as the “Cambrian explosion” of life.
    • Fossil record shows an enormous increase in the diversity of life forms during this time.
    • Oceans teemed with many types of animals.
paleozoic era1
Paleozoic Era…
  • Early Paleozoic Era
    • Vertebrates appeared.
    • Ferns and early seed plants appeared.
  • Middle Paleozoic Era
    • 4-legged animals appeared, i.e., amphibians.
  • Late Paleozoic Era
    • Reptiles appeared on land and flourished.
  • Largest mass extinction recorded marked the end of the Paleozoic Era.
paleozoic era2
Paleozoic Era

End of the Paleozoic Era:

  • Largest mass extinction recorded in the fossil record marked the end of the Paleozoic.
  • 90% of Earth’s marine species and 70% of the land species disappeared at this time.
mesozoic era
Mesozoic Era
  • Divided into three periods.
  • Triassic Period
    • Oldest period
    • Mammals appeared
    • Early mammals were small, mouselike
    • Dinosaurs and reptiles appeared
    • Ferns – huge fern forests
mesozoic era cont d
Mesozoic Era, cont’d…

Jurassic Period – middle of the Mesozoic Era

  • Modern birds evolved from one of the groups of dinosaurs.
    • This happened toward the end of this period.
    • Archaeopteryx
      • Small bird discovered in Germany
      • Had feathers, which is a birdlike feature
    • Present day bird – hoatzin, figure 14.8B, pg. 378
      • Reptilian features – claws on its wings – during its first few weeks of life
  • This evidence suggests that birds evolved from dinosaurs.
a mass extinction
A Mass Extinction!
  • Cretaceous
    • Last period of the Mesozoic Era
    • Many new types of mammals appeared
    • Flowering plants flourished
    • Mass extinction of dinosaurs marked the end of the Cretaceous Period
  • Scientists estimate that more than 2/3 of all living species during this time became extinct.
  • Cause of the Extinction?
    • One idea is that a large meteorite collision caused the mass extinction.
mass extinction cont d
Mass Extinction, cont’d…
  • A huge collision could have filled the atmosphere with thick, possibly toxic dust.
  • This would have changed the climate.
  • Many species would not have been able to survive the changed climate.
  • Large crater found in the waters off eastern Mexico
  • Crater was dated back to the Cretaceous Period.
  • Scientists believe this was the impact site.
changes during the mesozoic era
Changes During the Mesozoic Era
  • Geological events during this era changed the places where species lived.
  • These events affected the distribution of the species on Earth.

Theory of Continental Drift

  • Earth’s continents have moved during Earth’s history and are still moving today.
  • 6 cm per year
  • Same rate as the growth of hair
changes during the mesozoic era1
Changes During the Mesozoic Era
  • Early in the Mesozoic
    • The continents were merged into one large landmass.
    • The supercontinent broke up.
    • Pieces drifted apart.
  • Plate Tectonics – Theory that explains how the continents move.
plate tectonics cont d
Plate Tectonics, cont’d…
  • Earth’s surface is made of several rigid plates.
  • These plates drift on top of a fluid, partially molten layer of rock.
  • Plates are constantly moving.
    • Spreading apart
    • Sliding by
    • Or pushing against each other.
  • The movements affect organisms.
    • i.e., Descendants living on plates that are moving apart may be living in areas with very different climates.
cenozoic era
Cenozoic Era
  • Began about 65 million years ago.
  • Era in which we now live.
  • Mammals flourish in the early part of this era.
  • Primates appear – group of animals which humans belong to.
  • Primates have diversified greatly over the past 65 million years.
  • Modern man appeared approximately 200,000 years ago.