Transcript Macroevolution - San Diego Unified School District

Macroevolution
Biology 1-2
Macroevolution
 Macroevolution-evolutionary
changes on
a grand scale.


Including appearance of new groups, adaptive
radiation and mass extinction.
The evolution of diversity through speciation
and the development of new traits.
• The history of the major changes in life on Earth.
Fossil Record
 Fossil
record-record of evolution over
millions of years based on the order fossils
appear in the Earth.

Fossil-preserved remnant or impression of an
organism that lived in the past.
Fossil Record cont’d
 The
fossil record shows the changes that
have occurred in Earth’s history.

It shows the major changes in the surface of
the planet as well as the appearance and
disappearance of different groups of
organisms.
Radiometric Dating
 Radiometric
dating-use of radioactive
isotopes to determine the age of a fossil or
rock.

Isotope-version of an element with a different
number of neutrons.
Radiometric Dating cont’d
 Over
time, a radioactive isotope changes
into a nonradioactive form.

Half life-the amount of time it takes for 50% of
a radioactive sample to decay.
• Different elements have different half lives.
Radiometric Dating cont’d
 For
each half life that has passed, 50% of
the radioactive isotope decays.

E.g., if only one half of the radioactive isotope
remains, one half life has passed.
• 1/4 is two half lives, 1/8 is three half lives, etc.

How many half lives have passed gives the
age of the fossil.
Continental Drift

The surface of the Earth is constantly changing,
producing change in the organisms.

The surface of the earth is made of plates that move.
Continental Drift cont’d

Continental drift-change in
the position of the
continents caused by the
movement of the Earth’s
crust.
• Explains both the presence of
fossils of the same species on
different continents as well as
each developing its own
families.
Extinction and Radiation
 Changes
due to continental drift have
resulted in both mass extinctions and
explosions.

There have been about 12 episodes of mass
extinction.
• 6 in the last 600 million years.

Each was followed by an explosion in number
of species.
Extinction/Radiation cont’d
 The
surviving species have traits that
become the basis of adaptations to the
changed environment.

K-T extinction event (65 mya).
• The ancestors of the mammals and birds, along
with some of the reptiles, fishes and other groups
survive.
• Adaptive radiation happens as they take
advantage of the lack of competition.
Evolution of New Groups
 The
fossil record also shows the
development of new traits that lead to the
appearance of new groups of animals and
plants.

Natural selection only edits existing traits.
• Enough changes produces brand new traits.
Evolution cont’d
 Traits
appear with a use in one
environment but may have another use in
a different environment.


Allows the organism to survive in a new or
different environment.
An accumulation of new traits leads to the
appearance of new groups different from the
others.