Fossils

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Fossils
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What are fossils?

• The remains, imprints or traces of an organism
  that lived long ago.
• Preserved in rock.
• Typically sedimentary rock
• Must be buried quickly
• Types of fossils
• Molds
• Casts
• Carbonaceous film
• Petrified remains
• Original remains
• Trace fossils

Hard parts decay leaving behind a cavity in the
rock
Formed when the mold becomes filled
Thin film of carbon forms outline on rock
Minerals replace the original organism
The actual organism is preserved
Evidence of organism activity (footprint)
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Fossils in Sedimentary Rock

• Most fossils are preserved in sedimentary rock.
• Sedimentary rock usually forms when small
  particles of sand, silt, clay, or lime muds
  settle to the bottom of a body of water.
• As sediments build up, they bury dead organisms
  that have sunk to the bottom.

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Fossils in Sedimentary Rock

• As layers of sediment continue to build up over
  time, the remains are buried deeper and deeper.
• Over many years, water pressure gradually
  compresses the lower layers and turns the
  sediments into rock.

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How were entire organisms preserved?

• Original remains can be preserved in different
  materials.
• Ice
• Tar
• Amber

Tree sap
Iceman
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What are fossil fuels?

• Raw fuel that comes from the remains of once
  living organisms
• Solid
• Liquid
• Gas

Coal
Petroleum or Oil
Natural Gas or methane
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Why do scientists study fossils?

• Clues to the past
• Global changes regional changes
• Environmental
• Natural disasters
• Climate change
• Geologic
• Evolution

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How can relative age of rocks be determined?

• Using the law of superposition relative age can
  be determined
• Relative age is comparing one objects age to
  another.
• If there are three layers
• Top is youngest
• Then middle
• Bottom is oldest
• Index fossil is always found in a particular layer

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Relative Dating

• Lower layers of sedimentary rock, and fossils
  they contain, are generally older than upper
  layers.
• Relative dating places rock layers and their
  fossils into a temporal sequence.

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Relative Dating

• To help establish the relative ages of rock
  layers and their fossils, scientists use index
  fossils. Index fossils are distinctive fossils
  used to establish and compare the relative ages
  of rock layers and the fossils they contain.
• If the same index fossil is found in two widely
  separated rock layers, the rock layers are
  probably similar in age.

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Who Killed the Iceman?

• http//www.pbs.org/wgbh/nova/icemummies/iceman.htm
  l
• Picture article
• http//www.pbs.org/wgbh/nova/transcripts/2518icema
  n.html
• http//wilderdom.com/evolution/OtziIcemanAlpsPictu
  res.htm

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How is absolute age determined?

• The specific age of a rock or fossil
• Uses radioactive decay
• Half-life is the amount of time it takes for ½ of
  the mass of an element to decay into, more
  stable, element.
• The rate of decay can be measured
• Particular elements have a constant rate of decay
• Carbon-14 dating for living things
• Not always 100 accurate

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Geologic Time Scale
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Geologic Time Scale

• Geologists and paleontologists have built a time
  line of Earths history called the geologic time
  scale.
• The basic divisions of the geologic time scale
  are eons, eras, and periods.

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Divisions of the Geologic Time Scale

• The time scale is based on events that did not
  follow a regular pattern.
• The Cambrian Period, for example, began 542
  million years ago and continued until 488 million
  years ago, which makes it 54 million years long.
• The Cretaceous Period was 80 million years long.

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Naming the Divisions

• The Precambrian actually covers about 90 percent
  of Earths history.
• In this figure, the history of Earth is depicted
  as a 24-hour clock. Notice the relative length of
  Precambrian Timealmost 22 hours.

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Physical Forces

• The theory of plate tectonics explains how solid
  continental plates move slowly above Earths
  molten corea process called continental drift.
• Over the long term, continents have collided to
  form supercontinents. Later, these
  supercontinents have split apart and reformed.

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Geological Cycles and Events

• Continental drift has affected the distribution
  of fossils and living organisms worldwide. As
  continents drifted apart, they carried organisms
  with them.
• For example, the continents of South America and
  Africa are now widely separated. But fossils of
  Mesosaurus, a semiaquatic reptile, have been
  found in both South America and Africa.
• The presence of these fossils on both
  continents, along with other evidence, indicates
  that South America and Africa were joined at one
  time.

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Early Earth

• The Earth is estimated to be 4.6 billion years
  old

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Review of geologic time scale.
Precambrian Paleozoic Mesozoic Cenozoic

• Era
• Periods
• Epochs

Cambrian Ordovician Silurian Devonian Carboniferou
s Permian Triassic Jurassic Cretaceous Tertiary Qu
aternary
Paleocene Eocene Oligocene Miocene Pliocene Pleist
ocene Recent
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Geologic Time Scale(estimated years ago)

• 3.5 billion earliest evidence of life
• 540 million Paleozoic era begins
• 430 First land plant
• 245 Mesozoic era begins/Triassic period
• 208 Jurassic period

• 225First Dinosaurs
• 150 first birds
• 146 Cretaceous period
• 66 Dinosaurs extinct
• 66 Cenozoic era
• 60 Primates appear
• 200,000 Humans