1. Evidence for Evolution
Distribution and Fossils

2. Distribution
The distribution of living things on the globe provides information about the past histories of both living things and the surface of the Earth. This evidence is consistent not just with the evolution of life, but also with the movement of continental plates around the world-otherwise known as plate tectonics.

3. Plate Tectonics

4. Marsupials
Marsupials are a group of mammals that give birth to small young who develop inside a pouch
They evolved early in the history of mammals
Placental mammals, those that gestate young in the uterus, evolved from marsupials

5. hj

7. Which organism would have the advantage?
Marsupial or Placental Mammal?
Why?

8. Marsupial Distribution

10. Can You Explain Current Marsupial Distribution?

12. Methods of Dating
Absolute and Relative

13. How to measure age
A numerical (or "absolute") age is a specific number of years, like 150 million years ago. A relative age simply states whether one rock formation is older or younger than another formation.

14. Geologic Time Scale
The Geologic Time Scale was originally laid out using relative dating principles.

15. Absolute Dating
Absolute numerical dating takes advantage of the "clocks in rocks" - radioactive isotopes ("parents") that spontaneously decay to form new isotopes ("daughters") while releasing energy.

16. Radioactive Isotope
An unstable atom that will give off energy and decay into another type of atom.

17. Decay
Decay of the parent isotope Rb-87 (Rubidium) produces a stable daughter isotope, Sr-87 (Strontium), while releasing a beta particle (an electron from the nucleus). ("87" is the atomic mass number = protons + neutrons.

18. Rate of Decay Radioactive isotopes decay at constant rates
The rates are different for each type of isotope
A graph of isotope decay over time is called a decay curve

19. Decay Curve of U-238 to Pb-206

20. Using Decay to Calculate Age
Many minerals contain radioactive isotopes. In theory, the age of any of these minerals can be determined by: 
1) counting the number of daughter isotopes in the mineral, and  
2) using the known decay rate to calculate the length of time required to produce that number of daughters.

21. Half-Life
The amount of time it takes for 50% of the parent radioactive isotope to decay to its stable daughter isotope

22. Isotopes trapped in rocks are measured

23. How much U-235 is left after 2 billion years?

24. Carbon Dating
The radiocarbon dating method has evolved into the most powerful method of dating fossils, artifacts and geologic events up to about 50,000 years in age.

25. C-14 Dating
N-14 in the atmosphere is converted to C-14 by cosmic radiation
C-14 enters food chain through photosynthesis
C-14 decays back to N-14

26. What is the half-life of C-14?

27. Potassium- Argon Dating
In order to date older fossils, scientists must use other radioactive isotopes. A commonly used technique is called Potassium-Argon dating. The element potassium is found in most rock-forming minerals, and the half-life of the radioactive isotope Potassium 40 is 1.25 billion years, allowing measurable quantities of Argon 40 (its decay element, known as the daughter element) to accumulate in potassium-bearing minerals of almost all ages.

28. Drawbacks of Absolute Dating
Absolute Dating can only be performed in igneous rocks, not sedimentary rocks
Fossils older than 50,000 years cannot be dated, their age must be estimated using the surrounding rocks
Most fossils are found in sedimentary rock layers
Scientist then age the igneous rock layers above and below the fossil to determine an age range

29. Ok then, what are fossils and how do they form?
Think about it? What actually is a fossil? Do you know?
How does it form?
Write it down.
Share with a neighbor

30. How Fossils Form
Permineralization: replacement of tissues with minerals
Molds: sediments compact around tissues which dissolve and leave cast of organism
Trace: organism leaves evidence of its presence such as footprints

31. Memories of the Past

32. Memories of the Past

33. Memories of the Past

34. Tar Pits

35. Tar Pits

36. Trapped in Amber
Just like in Jurassic Park

37. Trapped in Ice
A 6-to-12-month-old male Mammoth, nicknamed Dima, found enclosed in a lens of ice six feet below the surface in Siberia in 1977, with grass and sand still in its mouth.

38. Conclusion
Living mammal distribution indicates periods of isolation, selection, and speciation
Fossils of ancient organisms are found everywhere, memories of earth’s rich heritage
Scientists can date the age of the rocks and thus begin to reconstruct the history of life on earth