1. Evolutionary Evidence
Part 1: Fossil Record

2. Bellringer
In your science journal, write and respond to the following question:
How do scientists learn about organisms of the past when studying fossils?

3. Objectives:
I can define fossil and explain why fossils are important pieces of evolutionary evidence.
I can identify the different types of fossils.
I can explain how fossils are formed.
I can describe two methods to determine the age of fossils.
I can explain why the fossil record is incomplete
I can analyze components of the fossil record and determine the sequence in which the organisms appear.

4. Section 15.1 Summary – pages 393-403
What are the different types of evidence used to support the evolutionary theory?
There are several places we can see indirect evidence of evolution/evolutionary relationships:
fossils,
biogeography,
similarities in anatomy,
biochemistry/DNA,
and embryology.
Section 15.1 Summary – pages

5. What is a fossil and why is it important?
A fossil is any preserved evidence of an organism that lived long ago found in the Earth’s rocks.
Plants, animals, and bacteria can form fossils.
The fossil record shows that some species from long ago are extinct today. Other species alive today are similar to those in fossils.

6. There are missing links even in fossil record.
Why does the fossil record not provide as much evidence as the other components of evolutionary evidence?
There are missing links even in fossil record.
Approximately 99% of the species that have ever lived are now extinct, but only a tiny percentage of that was preserved as fossils.
Most organisms decompose before they have the chance to become fossilized.

7. Section 14.1 Summary – pages 369-379
What are the different types of fossils?
TYPES OF FOSSILS
Fossils Types
Formation
A trace fossil is any indirect evidence
Trace fossils
left by an animal and may include a
footprint, a trail, or a burrow.
When minerals in rocks fill a space
Casts
left by a decayed organism, they make
a replica, or cast, of the organism.
A mold forms when an organism is
Molds
buried in sediment and then decays,
leaving an empty space.
Petrified fossils
Petrified-minerals sometimes penetrate
and replace the hard parts of an organism
Amber-Preserved or
At times, an entire organism was
quickly trapped in ice or tree sap that
frozen fossils
hardened into amber.
Section 14.1 Summary – pages

8. What are the different types of fossils?
Trace fossils – footprints, burrows, feces
Molds and casts – impressions or a mold filled with sediment
Replacement – original material replaced with mineral crystals
Petrified or Permineralized – empty pores are filled in by minerals
Amber – tree sap preserved
Original material – mummification or freezing

9. What are transitional fossils and why are they important?
Charles Darwin predicted that scientists would find fossils that would show organisms that were intermediates between different species.
Scientists today have found thousands of transitional fossils that contain features shared by different species.
Scientists have found intermediate species for the evolution of mollusks, modern horses, whales, and humans.

10. What are the classes of transitional fossils?
2 major classes of transitional fossils:
Derived traits
Ancestral traits
Derived traits are newly evolved features, such as feathers, that do not appear in the fossils of common ancestors.
Ancestral traits are more primitive features, such as teeth and tails, that do appear in ancestral forms.

11. Section 14.1 Summary – pages 369-379
Who studies fossils?
Paleontologists, scientists who study ancient life, are like detectives who use fossils to understand events that happened long ago.
They use fossils to determine the kinds of organisms that lived during the past and sometimes to learn about their behavior.
Section 14.1 Summary – pages

12. Section 14.1 Summary – pages 369-379
How are fossils formed?
For fossils to form, organisms usually have to be buried in mud, sand, or clay soon after they die.
Fossils are not usually found in other types of rock because of the ways those rocks form.
For example, the conditions under which metamorphic rocks form often destroy any fossils that were in the original sedimentary rock.
Most fossils are found in sedimentary rocks These rocks form at relatively low temperatures and pressures that may prevent damage to the organism.
Section 14.1 Summary – pages

13. How are fossils formed?
Fossils do not form in igneous or metamorphic rock; they will not survive the heat or pressure involved in the formation of these kinds of rocks.
Fossils are formed in sedimentary rock.

14. Section 14.1 Summary – pages 369-379
Why is it that not all organisms become fossils?
Few organisms become fossilized because, without burial, bacteria and fungi immediately decompose their dead bodies.
Occasionally, however, organisms do become fossils in a process that usually takes many years.
“How fossils form” Right click the above link and open the hyperlink to look at an interactive lesson on fossil formation
Section 14.1 Summary – pages

15. Section 14.1 Summary – pages 369-379
What are the methods in which scientists use to determine the age of a fossil?
Relative dating
This method is used to determine the age of rocks by comparing them with those in other layers
This method basically indicates that the fossils found closer to the surface are younger, and the fossils found in deeper strata are more primitive (older)(in undisturbed ground)
This method does not give a specific age of the fossil or rock.
Section 14.1 Summary – pages

16. Section 14.1 Summary – pages 369-379
What are the methods in which scientists use to determine the age of a fossil?
RELATIVE DATING
Section 14.1 Summary – pages

17. What are the methods in which scientists use to determine the age of a fossil?
Using this principle of relative dating, scientists can determine relative age and the order of appearance of the species that are preserved as fossils in the layers.
The law of superposition states that younger layers of rock are deposited on top of older layers.

18. Section 14.1 Summary – pages 369-379
What are the methods in which scientists use to determine the age of a fossil?
Radiometric dating
This method uses the decay of radioactive isotopes of atoms to measure the absolute age of a rock.
To find the specific ages of rocks, scientists use absolute dating, also called Radiometric Dating.
As specific atoms decay they emit radiation and lose electrons, which causes them to turn into a different element.
So- these atoms change from one thing into something else over time- and they do this at a constant rate.
Section 14.1 Summary – pages

19. What are the methods in which scientists use to determine the age of a fossil?
The half-life of a radioactive atom is the time it takes for half of that atom in a sample to decay and turn into another element.
Radioactive isotopes are found in igneous and metamorphic rock, not sedimentary, and cannot be used to date fossils.

20. It takes 5,730 years for ½ of Carbon 14 to turn into Nitrogen 14
If you know what the unstable atom is (Carbon 14) and you know what it turns into as it decays (Nitrogen 14).
And you know the rate at which the unstable atom decays/turns into something else
You can measure the amount of the unstable atom in the rock….and compare that to the amount of the new atom
This will tell you the age of the sample rock.
It takes 5,730 years for ½ of Carbon 14 to turn into Nitrogen 14

21. Most radioactive isotopes have rapid rates of decay (that is, short half-lives) and lose their radioactivity within a few days or years.
Some isotopes, however, decay slowly, and several of these are used as geologic clocks. The parent isotopes and corresponding daughter products most commonly used to determine the ages of ancient rocks are listed below:
Parent Isotope
Stable Daughter Product
Currently Accepted Half-Life Values
Uranium-238
Lead-206
4.5 billion years
Uranium-235
Lead-207
704 million years
Thorium-232
Lead-208
14.0 billion years
Rubidium-87
Strontium-87
48.8 billion years
Potassium-40
Argon-40
1.25 billion years
Samarium-147
Neodymium-143
106 billion years

22. What is stasis?
Stasis is the term used to describe a period of time during which organisms don’t seem to change their forms during a lengthy presence in the fossil record.

23. What Fossils can show us
Gradualism- evolution at a slow and more steady rate

24. OR…..
Punctuated Equilibrium- stable environments followed by rapid change periods. (predation pressure, food supply and climate

25. What can an incomplete fossil record indicate?
The sudden disappearance of many life forms in the fossil record suggests that a mass extinction occurred. For those species that survived a mass extinction, new ecological niches became available. This may have led to rapid evolution, which would appear to be a “sudden appearance” in the fossil record of many different species, also known as adaptive radiation

26. What is adaptive radiation?
Adaptive radiation - the evolutionary division of a group of organisms into diverse groups over a short period of geologic time