The Age of Earth
Classification Quick Quiz
Write the letter of the correct definition
below the number of the correct
corresponding term.
Remember to write your name on your
paper before you submit your answer
sheet.
The crime?
The Crime?
Fossil Evidence
Two Types:
•Sedimentary – organisms that have died,
been covered with sediment
and then decomposed.
•Whole -
When an organism is
covered whole in amber and
semi preserved.
Sedimentary Fossils
Amber Fossils
What Stories do Fossils
Reveal?
What Fossils Can Reveal
– The fossil record contains an enormous amount
of information for paleontologists, researchers
who study fossils to learn about ancient life.
– By comparing body structures in fossils to body
structures in living organisms, researchers can
infer evolutionary relationships.
– Bone structure and trace fossils, like footprints,
indicate how animals moved.
– When different kinds of fossils are found
together, researchers can sometimes
reconstruct entire ancient ecosystems.
TIME PLAYS A BIG FACTOR HERE
Dating Earth’s History
• How do we date events in Earth’s history?
Dating Earth’s History
• How do we date events in Earth’s history?
•Relative dating allows paleontologists to
determine whether a fossil is older or younger
than other fossils.
•Radiometric dating uses the proportion of
radioactive to non-reactive isotopes to calculate
the age of a sample.
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.
Radiometric Dating
– Relative dating is important, but provides no
information about a fossil’s absolute age in years.
– One way to date rocks and fossils is radiometric
dating.
– Radiometric dating relies on radioactive isotopes,
which decay, or break down, into non-radioactive
isotopes at a steady rate.
– Radiometric dating compares the amount of
radioactive to non-reactive isotopes in a sample to
determine its age.
– A half-life is the time required for half of the
radioactive atoms in a sample to decay.
Radiometric Dating
– The half-life of
potassium-40 is
1.26 billion years.
Radiometric Dating
– Carbon-14, which has a short half-life, can
be used to directly date very young fossils.
– Elements with long half-lives can be used to
indirectly date older fossils by dating nearby
rock layers, or the rock layers in which they
are found.
Geologic Time Scale
– How was the geologic time scale established,
and what are its major divisions?
– The geologic time scale is based on both
relative and absolute dating. The major
divisions of the geologic time scale are eons,
eras, and periods.
Geologic Time Scale
– Geologists and
paleontologists have
built a time line of
Earth’s history called
the geologic time
scale.
– The basic divisions
of the geologic time
scale are eons, eras,
and periods.
Naming the Divisions
– The Precambrian actually covers about 90
percent of Earth’s history.
– In this figure, the history of Earth is depicted
as a 24-hour clock. Notice the relative length
of Precambrian Time—almost 22 hours.
Life on a Changing Planet
How have our planet’s environment and living
things affected each other to shape the history
of life on Earth?
Life on a Changing Planet
– How have our planet’s environment and living
things affected each other to shape the history of
life on Earth?
– Building mountains, opening coastlines,
changing climates, and geological forces have
altered habitats of living organisms repeatedly
throughout Earth’s history. In turn, the actions of
living organisms over time have changed
conditions in the land, water, and atmosphere of
planet Earth.
Physical Forces
Climate and Temperature
– “Heat wave” of the Mesozoic Era, Earth’s
average temperatures were only 6°C to 12°C
higher than they were during the twentieth
century.
– During the ice ages, world temperatures were
only about 5°C cooler than they are now.
– These relatively small temperature shifts
changed the shape of life on Earth.
Physical Forces
– Geological forces have transformed life on
Earth, producing new mountain ranges and
moving continents.
– Volcanic forces have altered landscapes and
even formed entire islands.
– Local climates are shaped by the interaction
of wind and ocean currents with geological
features such as mountains and islands.
Physical Forces
– The theory of plate tectonics explains how
solid continental “plates” move slowly above
Earth’s molten core—a process called
continental drift.
– Over the long term, continents have collided
to form “supercontinents.” Later, these
supercontinents have split apart and
reformed.
Biological Forces
–
The activities of organisms have affected global environments.
–
For example, Earth’s early oceans contained large amounts of
soluble iron and little oxygen.
–
During the Proterozoic Eon, however, photosynthetic
organisms produced oxygen gas and also removed large
amounts of carbon dioxide from the atmosphere.
–
The removal of carbon dioxide reduced the greenhouse effect
and cooled the globe. The iron content of the oceans fell as iron
ions reacted with oxygen to form solid deposits.
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