The History

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The History of Earth
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A Little Bit of History

• The history of geologic time begins with the
  human interest
  
  in mining.
• Interests in rock units began to flourish with
  commercial mining in the 1500s and 1600s
• People began to identify strata (rock layers) by
  the types of fossils that were found within them.
• Two scientists were credited with contributing
  the most research to this area -- Nicolaus Steno
  and James Hutton
• .

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Nicolaus Steno

• Adapted two geologic principles
• Law of Superposition sedimentary rocks are
  found with the oldest on the bottom and youngest
  on top. E.x. Paint layers
• Principle of Original Horizontality If left
  undisturbed rock layers will stay in horizontal
  order

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James Hutton

• 18th-century Scottish
• physician and farmer
• Studied his farm land for geologic changes
• The Present is the Key to the Past
• Principle of Uniformitarianism geologic
  processes from the past are the same as the
  current geologic processes.
• E.x. What happened then happens now

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Relative Age gives the age of a rock layer based
on the ages of layers around it (younger or older)
What sort of events can change the order of rock
layers?
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Law of Crosscutting Relationships

• Fault or body of rock is younger than any other
  body of rock that it cuts through.
• Igneous intrusions that may be uplifted to the
  surface would also be younger than the rock they
  push through

Unconformities- breaks in geologic time where
rock layers erode away or when sediment isnt
deposited
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The Fossil Record
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Paleontology

• The study of fossils.
• Fossils remains of plants
• and animals that lived in a previous geologic
  time
• Organisms have changed throughout the geologic
  past.
• Fossils provide the clues behind environmental
  changes of the past.
• What kinds of rocks are fossils found in?

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Fossilization

• Organisms with hard parts are typically
  preserved.
• Those without hard parts are fossilized by quick
  burial.
• How are fossils formed?
• Mummification
• Amber
• Tar seeps
• Freezing
• Petrification

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Mummification
Drying of organisms found in deserts.
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Amber
Hardened tree sap, insects get stuck in sap and
sap hardens
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La Brea Tar Pits

• Thick petroleum
• Animals get stuck in tar and it preserves them

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Freezing
Animals preserved because bacteria cannot survive
in cold climate to decay the bodies
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Petrification
When organic material is replaced with minerals
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Types of fossils

• Trace Fossils
• -Evidence that
• an animal existed.
• Ex. footprints

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Types of Fossils continued

• Molds animal remains dissolve away, but the
  shape of the animal remains.
• Cast when a mold fills in with sediment and
  becomes hardened.

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Imprints- carbonized imprints

• Coprolites

fossilized animal droppings (learn eating habits)
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Gastroliths- stones found in dinosaur stomachs to
help them digest food(are generally round and
polished)
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Index fossil Unique fossil that lived during a
specific time
Trilobites lived 750 million years ago
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Specific index fossils for every time period
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The Geologic Time Scale is a type of calendar
geologists use to put events in their proper order
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Calculating Earth's Age

• Earths age was estimated by measuring the
  radioactive decay of uranium to lead.
• With improved techniques and evidence from tree
  rings and glaciers, the age of Earth is estimated
  to be about
• 4.5 4.6 billion years old.

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Geologic Column

• By applying relative ages to sedimentary rocks we
  began to look at fossils to learn to date them.
• Not one place contains a complete record of
  geologic time.
• Geologic Column- ordered arrangement of rock
  layers based on relative ages of the rock
• Once geologists have dated a lot of the rock
  layers, they can fill in the gaps.

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Divisions of Geologic Time

• Geologic time is typically divided by clear
  changes.
• Ex. extinctions and dominant fossils

• MYA- millions of years ago
• BYA- billions of years ago

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Divisions of Geologic Time cont

• Eons largest unit of geologic time (4 total
  eons).
• We call the first three eons the Precambrian time
  which has little fossil evidence.

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Microbe-rich stromatolite reefs, like this one in
Shark Bay, Australia, were among the first
sources of oxygen on Earth. They flourished
throughout the planet's shallow waters 3.5
billion years ago, but are extremely rare today.
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Continued

• Era- Unit of time that includes two or more
  periods.
• There are 3 eras that the Phanerozoic Eon can be
  divided into
• Paleozoic Zoic animal life
• Mesozoic
• Cenozoic.
• Different fossils are represented in each of
  these eras marine life, birds and reptiles and
  mammals.

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Paleozoic explosion of diverse life

• Beginning
• Oceans
• Middle to the End
• Forests and jungles
• Land animals evolved

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Devonian Period Age of Fishes
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Mesozoic Age of Reptiles
Jurassic Period
Dinosaurs ruled the Earth
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Cenozoic Age of
Mammals
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• Eras are divided into shorter time units called
  Periods.
• Each period is characterized by specific fossils
  and is named for the location they were
  discovered.
• Epochs-when the fossil record is so complete we
  can keep dividing periods into epochs.

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