1. 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.

2. Separation, Adaptation, Division - Speciation
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.”

3. Forming a New Species, continued
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.

4. Forming a New Species, continued
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.

5. Two methods : Relative Dating, Absolute Dating
Section 1 Geologic History
How do scientists determine the age of objects (like fossils) in sedimentary rocks?
Two methods : Relative Dating, Absolute Dating

6. 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.

7. Using Fossils to Date Rocks
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.

8. Relative Dating, continued
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.

9. 2. Absolute Dating Use of Carbon-14 and Uranium-238
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.

10. Absolute Dating, continued
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.

11. Absolute Dating, continued
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.

12. Section 1 Geologic History

13. Absolute Dating, continued
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.

14. 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.

15. Section 1 Geologic History