The History of Life

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The History of Life

• Ch 14

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Earths Early History

• Evolution is a scientific THEORY based on
  different types of evidence collected over the
  years
• Evidence Includes
• Earth was an inhospitable planet
• Hot
• Volcanic gasses
• First organisms appeared between 3.5 to 3.9
  billion years ago
• There is direct evidence of Earths history
• Fossils rocks show that Earth formed about 3.9
  billion years ago

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History in Rocks

• Fossils any evidence of an organism that lived
  long ago
• Trace fossils something left by an animal
  (example footprint, trail, burrow)
• Casts minerals in rocks fill a space left by a
  decayed organism (form a replica of organism)
• Petrified fossils minerals replace the hard
  parts of an organism
• Imprints thin objects can leave an imprint as
  sediments turn to rocks
• Amber-preserved frozen actual organism is
  trapped in amber or ice

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Dunkleosteus (30 ft long bony skull shown here
is about 1 meter high) Extinct at the end of the
Devonian
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Fossil examples
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Studying fossils

• Paleontologists study fossils
• Kinds of organisms that lived
• Learn about behavior
• Earths climate
• Geography (rivers, continent position)
• Fossils are found in sedimentary rock
• Organism is buried in mud, sand, or clay soon
  after death
• Particles compress harden over time to form
  sedimentary rock

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Determining Fossil Age

• Relative dating
• Surface layers are newest so they have the most
  recent fossils.
• Deeper layers contain older fossils
• Scientists can determine the order of appearance
  extinction
• Radiometric dating
• Uses radioactive isotopes
• Potassium 40 (half life of 1.3 billion yrs)
• Carbon 14 (half life of 5730 years)
• Scientists can approximate ages

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The Geologic Time Scale

• A time scale of Earths existence based on fossil
  evidence
• 4.6 billion years ago present
• Divided into Eras
• Precambrian, Paleozoic, Mesozoic, Cenozoic
• Distinguished by organisms that lived during the
  era
• Eras are divided into periods
• Mass extinction entire groups of organisms
  disappear from the fossil record almost all at
  once

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Precambrian Era

• 87 of Earths history
• 3.5 billion years ago to 544 million years ago
• Began with prokaryotes
• Eukaryotes developed and flourished
• Soft-bodied invertebrates (jellyfish, sponges)
• Oldest fossils 3.5 billion years old
• resemble forms of modern species of cyanobacteria
• Stromatolites evidence of photosynthetic
  bacteria

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Paleozoic Era

• Beginning (Cambrian period)
• Dramatic increase in diversity of life forms
• Worms, sea stars, trilobites in the oceans
• Fish appeared oldest animals with backbones
• Land species ferns seed plants
• Middle amphibians
• End Reptiles
• Largest mass extinction 90 of Earths marine
  species 70 of the land species disappeared

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Mesozoic Era

• Began about 245 million yrs ago
• Triassic
• Mammals appeared on Earth
• Early mammals were small and mouse-like
• Jurassic (began 280 million years ago)
• Age of the Dinosaurs
• Birds appeared
• Evidence of bird relation to dinosaurs
• Cretaceous (began 144 million years ago)
• New types of mammals flowering plants
• Mass extinction of dinosaurs 66 million years
  ago

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Geological Events of the Mesozoic

• Geologic evidence of a large crater East of
  Mexico
• Could have filled the atmosphere with dust,
  changing climate
• Continental Drift
• Pangaea broke apart continents began to move
  apart
• Plate tectonics Earths crust consists of
  several rigid plates on top of molten rock.
• Plates continuously move
• Explains continental drift

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Cenozoic Era

• Began 66 million years ago the current era
• Mammals began to flourish
• Primates appeared (30 million years ago)
• Modern humans appeared (200,000 yrs ago)

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14.2 Origin of Life
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The Origin of Life on Earth

• Abiogenesis life from non-living things and
  Spontaneous Generation idea that nonliving
  material can produce life
• Disproven by Redi and Pasteur
• Primordial Soup natural processes formed early
  organic compounds
• Miller-Urey experiment
• Biogenesis living organisms only come from
  other living organisms

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Redi Pasteur
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The Origin of Cells

• Prokaryotes Archaebacteria (1st cells)
• Eukaryotes endosymbiont hypothesis
• Separate DNA in chloroplasts and mitochondria
• Both organelles the same size and shape of
  bacteria