Transcript unit-two-test-fill-in

Chapter 4
Section 3 Natural Selection in Action
Forming a New Species
• It has been suggested that, sometimes, drastic
changes that can form a new species take place.
• Under this idea, a new species may form after a
group becomes separated from the original
population.
• The formation of a new species, suggested to have
happened long ago as a result of change over
time, is called speciation.
Chapter 4
Section 3 Natural Selection in Action
Separation, Adaptation, Division - Speciation
1. Separation Speciation is believed to begin when a part
of a population becomes separated from the rest.
2. Adaptation Populations constantly undergo natural
selection. After two groups have separated, natural
selection continues to act on the groups.
• If the environmental conditions for each group differ, the
groups’ adaptations might differ. According to scientists
at UC Berkeley, “We can only put together part of the
story from the available evidence.”
Chapter 4
Section 3 Natural Selection in Action
Forming a New Species, continued
3. Division Over many generations, two separated
groups of a population may become very different
through natural selection.
• Even if a geological barrier is removed and the
groups are reunited, they may no longer be able to
interbreed.
• If they cannot interbreed, the two groups are no
longer the same species.
Chapter 4
Section 3 Natural Selection in Action
Forming a New Species, continued
3. Division Over many generations, two separated
groups of a population may become very different
through natural selection.
• Even if a geological barrier is removed and the
groups are reunited, they may no longer be able to
interbreed.
• If they cannot interbreed, the two groups are no
longer the same species.
Chapter 5
Section 1 Geologic History
• How do scientists determine the age
of objects (like fossils) in
sedimentary rocks?
• Two methods : Relative Dating,
Absolute Dating
Chapter 5
Section 1 Geologic History
• 1. Relative dating
• Fossils in different rock layers have
different ages. Oldest at the bottom.
• The age of the rock around the fossil
tells how old the fossil is.
• Using rocks to date the fossils.
Chapter 5
Section 2 Looking at Fossils
Using Fossils to Date Rocks
• Scientists have found that particular types of fossils
appear only in certain layers of rock.
• By dating rock layers above and below these
fossils, scientists can determine the time span in
which the organism lived.
• If the organism lived for a relatively short period of
time, its fossils would show up in limited layers.
Chapter 5
Section 1 Geologic History
Relative Dating, continued
• The bottom layers of rock: usually the oldest
• The top layers: usually the youngest.
• The order/sequence of rock layers determine the
relative age of objects within the layers.
• For example, fossils in the bottom layers are
usually older than fossils in the top layers.
• The rock tells the age of the fossil.
Chapter 5
Section 1 Geologic History
2. Absolute Dating
• Use of Carbon-14 and Uranium-238
• Thought to be more precise dating method.
• For fossils, rocks, and other things
• Activity of atoms used to measure the age of
fossils or rocks in years.
• Atoms are the particles that make up all matter.
Chapter 5
Section 1 Geologic History
Absolute Dating, continued
• Some atoms are unstable, and will decay over time.
• When an atom decays, it becomes a different and
more stable kind of atom.
• Each kind of unstable atom decays at its own rate.
Chapter 5
Section 1 Geologic History
Absolute Dating, continued
• Half-life: The time it takes for half of the unstable
atoms in a sample to decay
• Scientists compare amounts/ratio of unstable to
stable atoms.
• Since they know the half-life, they can determine the
approximate age of the sample.
Chapter 5
Section 1 Geologic History
Chapter 5
Section 1 Geologic History
Absolute Dating, continued
• Uranium-238
used to date rocks or fossils
thought to be millions of years old.
• Longer half-life than carbon-14
• Carbon-14 has a half-life of only 5,780
years.
• Used to date fossils and other objects that are
less than 50,000 years old, such as human
artifacts.
Chapter 5
Section 1 Geologic History
• The Geologic Column : combination of
data from all of the known rock sequences
around the world.
• An idealized sequence, a picture of rock
layers that contains all of the known fossils and
rock formations on Earth.
• These layers are arranged from oldest to
youngest.
Chapter 5
Section 1 Geologic History