A. Direct EvidenceB. Indirect Evidence

Visible evidence that takes us back in time and shows organisms have changed

Ex. – Fossils

▪ Paleontologists are scientists who collect and study fossils.

▪ The fossil record provides incomplete information about the history of life.

▪ Over 99% of all species that have lived on Earth have become extinct.

▪ Where are all these fossils??

Fossil FormationWater carries small rock particles to lakes and seas.

Fossil Formation

Dead organisms are buried by layers of sediment, which forms new rock.

The preserved remains may be later discovered and studied.

Lucy

Coal Formation

The following picture is of plant fossils found in coal from the Minto area that are 300 million years old…..older than dinosaures!

Relative Dating

▪ In relative dating, the age of a fossil is determined by comparing its placement with that of fossils in other layers of rock.

▪ Rock layers form in order by age—the oldest on the bottom, with more recent layers on top.

▪ Grand Canyon

Relative dating allows paleontologists to estimate a fossil's age

compared with that of other fossils.

▪ Radioactive dating (Absolute Dating)

▪ Some elements are radioactive and steadily break down into nonradioactive elements.

▪ Radioactive dating is the use of half-lives to determine the age of a sample.

▪ A half-life is the length of time required for half of the radioactive atoms in a sample to decay.

C-14 breaks down into N-14 at a fixed rate.

The half life of C-14 is 5,760 years.When an organism dies, the C-14 in

the organism starts to change into N-14.

Knowing the half-life, you can compare the amount of C-14 to N-14 to determine the age of the fossil

Let’s say the fossil we are dating shows 50% C-14 and 50% N-14…….

The fossil should be 5,760 years old. If another 5,760 years passed, what

would be the ratio of C-14 to N-14?Right!!.........C-14 25% to N-14 75%Potassium 40 is an isotope with a

half-life of 1.2 billion years!!

Evidence we can look at today that suggests we may have a common ancestry with other organisms.

1. Embryological Similarities

2. Comparative Morphology

Homologous Structures

(Similar structure but different function!)

Similar in function but not in structure

Do not show the close evolutionary connection

Analogous Structures

3. Similarities in Biochemistry (Organic Compounds)

DNA similarities (98% of our DNA is the same as a chimpanzee)

Protein in all organisms is composed of the same 20 amino acids!!

Direct Evidence – something we can look at that takes us back in time.

Ex. Fossils

Indirect Evidence – something we can look at that show some kind of evolutionary connection between organisms.

Ex. Embryological similarities, Homologous structures, Biochemistry similarities

Darwin’s explanation of evolution is called Natural Selection.

What does the term Artificial Selection mean? Discuss this with a neighbour.

Samuri Crab

Organisms don’t change to survive, they survive (or die!) because they change!