Transcript Chapter Eight

Fossils
How does a fossil form?
• Living things die and are buried by
sediment.
• The sediment hardens into rock preserving
the shape of the organism.
How do mold and a cast fossils
form?
• A mold fossil forms when the hard part of the
•
organism is buried in sediment. (Ex: a bone or a
shell)
Cast fossils: Groundwater contains dissolved
minerals and sediment. The water seeps into an
empty mold and deposits the minerals and
sediment into a cast fossil. It forms a solid copy
of the shape.
Types of fossils
• Mold Fossil
Cast Fossil
Petrified fossils and trace fossils
• Petrified means it turned into stone.
• Ground water deposits the minerals which
in turn replaces all or part of the
organism.
• Trace fossils: provide evidence of the
animals activities. Ex: a footprint.
How are carbon films formed?
Sediment buries an organism
Material that makes up
organism=> gas.
Gas escapes sediment.
Leaves carbon behind.
This can preserve plant leaves
and insects.
Preserved remains
• BBC - Science & Nature - Making fossils
• Animals that were trapped in tar. The tar
preserved bones from decaying
• Animals that were frozen. These animals
had hair and skin preserved.
Preserved remains
Amber: hard resin, sap,
of an evergreen tree
Insect trapped in resin
Insect dies
More resin covers insect
The resin protects the organism
from decay.
How do paleontologists determine
changes over time?
• Paleontologists collect fossils to determine
the characteristics of past life forms.
• Information that paleontologists gather
about past lives is called the fossil record.
• The fossil record provides evidence about
organisms changing over time, history of
life, and the past environments. Ex: coal
found in Antarctica.
Is there an order of fossils?
• Fossils occur in a particular order.
– Older rocks have simple organisms.
– Younger rocks have more complex organisms.
• Evolution gradually changes things over
time. Ex: Gal. lizards.
• Extinction: no longer exists. Ex: Chinese
freshwater dolphin
Can you make a fossil?
• BBC - Science & Nature - Burying bodies
Venn Diagram Activity
• In your notes complete the following:
– Create Venn Diagrams comparing the
following types of fossils.
• Mold Fossils vs. Cast Fossils
• Petrified Fossils vs. Trace Fossils
• Carbon Films vs. Preserved Remains
• You may use your notes to complete the Venn Diagrams.
Extinction
Evolution
Relative Age of Rocks
• The relative age of rocks would be the age
compared to the age of other rocks.
• Law of superposition: In a horizontal
sedimentary rock layer, the oldest layer is
at the bottom. Thus the higher layers are
younger.
How do paleontologists determine
relative age?
• Oldest layer on the bottom and newest layer at the
surface.
This is true if the following situations don’t occur.
• 1. Extrusion: magma beneath the surface
flows onto the surface. Exits the ground
• 2. Intrusion: Magma pushes bodies of
rock. Magma cool, hardens, into the mass
of igneous rock. Which is always younger.
3. Faults: break in the Earth’s crust. Forces
inside the Earth causes movement of rock.
Fault is always younger than the rock it
cuts through.
What are gaps in the geologic
record?
• Unconformity: gaps in the geological
records. Some rock layers are lost due to
erosion.
• Index fossils: help geologist match layers
of rocks and tell the relative age. They
represent an organism that existed briefly
and was widely distributed. Ex: Ammonite
fossils.
What are the types of
unconformities?
• Angular Unconformities:
• Rock layers are tilted.
• Tilted rock layers are eroded.
• New sediment deposited on top.
• Disconformities:
• Gaps missing in parallel rock layers.
• Nonconformities:
• Sedimentary rock deposited on top of an eroded layer.
Parallel vs. Perpendicular Lines
• Parallel Lines- Two lines in a plane that never
intersect or cross.
• Perpendicular Lines: Lines that intersect at right
angles.
Angles
• Acute Angles: Have measures less than 90 degrees.
• Right Angles: Have measures equal to 90 degrees.
• Obtuse Angles: Have measures between 90 to 180
degrees.
Name that Unconformity
What type of unconformities do you see in this picture?
Do you see any parallel lines or perpendicular lines?
Do you see any angles in the picture?
What type of unconformity is shown in this picture?
Do you see any perpendicular or parallel lines?
Do you see any angles in the picture?
What type of unconformity is being shown here?
Do you see any parallel or perpendicular lines?
Do you see any angles in the picture?
What type of unconformity is being shown here?
Do you see any parallel or perpendicular lines?
Do you see any angles in the picture?
Absolute Age of Rocks
• Absolute Age: Is the age, in years, of a rock or
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other objects.
How do scientist find absolute age?
– Radiometric Dating: The process of
calculating the ratio of parent isotope to
daughter isotope in a mineral.
What is Radiometric Dating?
• Radiometric dating determines the absolute age
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of rocks.
Half life: The time is takes for half of the atoms
in the isotope to decay.
• *Paper demo on half-life.
• Potassium-40: used to date rocks because it has
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a long half life. (Used to date rocks)
Carbon 14: used to date organisms up to 75,000
years old. (Used to date bones, wood, and
charcoal)
Calculate Absolute Age
• The half-life of potassium-40 is 1.3 billion years. An
igneous rock is found 25% potassium-40 and 75%
daughter product. Calculate the absolute age of this
rock.
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•
•
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1 half-life
2 half-life
3 half-life
4 half-life
daughter
=
=
=
=
50% parent material left- 50% daughter
25% parent material left- 75% daughter
12.5% parent material left- 87.5% daughter
6.25 % parent material left- 93.75 %
Can all Rocks be Radiometrically
Dated?
• No, sedimentary rocks can’t be dated this
way because they are made of too many
parent rocks.
• Radiometrically Dated Rock:
– Igneous Rocks
– Metamorphic Rocks
Geologic Time scale
• The geologic time scale was developed by
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scientist studying rock layers and index fossils
world wide.
Precambrian time was 88% of the Earth’s
history, 544 million years ago.
How is the Geological Time
Scale Divided?
• The Geological Time Scale is divided by
time periods: longest to shortest.
• Eon- Longest time period.
• Era- Next longest, marked by major changes in
fossils present.
• Period- Next longest, characterized by the type of
life that existed.
• Epochs- A division of a period.
What are the major events in Paleozoic
Era?
• A variety of organism evolved
• The first vertebrate evolved => Jawless
fish
• Land plants, insects and spiders, appeared
• Lungfish first vertebrate to crawl onto
land.
• Reptiles, winged insects, forests.
• Mass Extinction: Affected both plants
and animals. Scientist hypothesize =>
Pangaea.
• Pangaea: the Earth’s continents moved
together to form one large land mass.
Paleozoic Era
• Jawless fish
Pangaea
What are the major events in the
Mesozoic Era?
• Known as the Age of Reptiles
• 225 million years ago first dinosaur
• Mammals first appeared: Morganucodon
• Birds first appeared: Achaeopteryx
• Mass Extinction: Scientist hypothesize that
objects from space struck the Earth.
What were the major events in the
Cenozoic Era?
• Mammals evolved to live in the water, land,
and in the air.
• Earth’s climate cooled due to a series of ice
ages.
• Modern humans evolved 100,000 years ago.
• 12,000 to 15,000 humans migrated around the
world except Antarctica.