Lecture #6 Time Scales/Fossil Record

Lecture #6—Time Scales/Fossil Record

The next several lectures deal with the current evidence showing unequivocally that evolution by natural selection has occurred. In this lecture we fill in two major weak pieces of Darwin’s argument: How old is the Earth? Where are the transition fossils between major groups of organism?

Determining the age of rocks and fossils

Until radioactive methods were developed, geologists did not know the absolute dates of rocks, fossils and the earth. They could determine only their relative ages by noting that the oldest layers must be the deepest ones. In the 1950’s with the aid of radioactive dating the real ages of rocks could be established.

You need to be able to explain this system of measurement.

You need to be able to give at least 3 reasons why scientists believe the system is accurate.

Transitional Fossils.

You need to be able to explain what a transitional fossil is and why it is important.

You need to be able to identify why transitional fossils are hard to find. Darwin identified several reasons and we now can list more.

Darwin introduced the idea of a branching family tree (a phylogeny) depicting the pattern of inheritance of a group of organisms. Explain what this suggests about finding transitional species.

Can you describe the key steps in the evolution of whales?

Define these terms/concepts

Radioactive dating Half-life Phylogeny Isotope Can you answer these questions?

1) Explain why the carbon 14 method of radioactive dating cannot be used to date most rock samples.

2) Give 3 methods that are used to check and see if radioactive dating methods are giving credible results.

3) Explain 3 three reasons that transition fossils are difficult to find.

4) Here is a diagram from the Origin of Species. Explain what is being depicted with species labelled “H”. How does this differ from what happened with species “I”? How many species appear to have survived until the time horizon labeled “X”?

5) Whale ancestors were originally land animals. Discuss three major adaptations that occurred in their anatomy and physiology in order for them to be today’s successful aquatic mammals. What type of transitions were necessary on the way to make this possible?

6) Here is a proposed phylogeny for whales. According to this diagram, when in time did the first modern whales appear? How did you determine this? What date would you say the first ancestral whale appeared? Are hippopotamuses more closely related to whales than walruses? How can you tell? 7) What does it mean to say that the half of uranium 232 is 4.5 billion years?