1. Fossil Evidence

• Fossils are the remains of plants or animals that lived a long time ago or the evidence of them.

• Hard parts of the organism are replaced by minerals.

Prediction: If life has changed over time then we should find evidence of organisms different from those found today.

shells leaves and seeds

bones and teeth

tree trunks and branches

fossilized footprints and burrows

fossilized animal droppings

RELATIVE DATING

YOUNGEST ROCK LAYER

OLDEST ROCK LAYER

ALLOWS ONE FOSSIL TO BE COMPARED TO ANOTHER…FOR EXAMPLE—THE SHELL IS OLDER THAN THE HORSE, BUT YOUNGER THAN THE FISH. WE DON’T KNOW THE EXACT AGE, JUST THE RELATIVE AGE

TOP

BOTTOM

Sedimentary Rock is formed in layers - the older beds are on the bottom, and the younger beds are on the top.

Radiometric Dating• Radioactive Decay: Naturally-occurring

radioactive materials break down into other materials at known rates.

• Many radioactive elements can be used as geologic clocks.

• Time can be estimated by measuring the amount of radioactive element in a sample.

• Half Life = Amount of time it takes for half of the radioactive element to decay

Uranium 235 Half life = 704 million yearsLead 207

Carbon 14 Nitrogen 14 Half life = 5730 years

= Carbon 14(radioactive)

= Nitrogen 14 (stable)

= Carbon 14(radioactive)

= Nitrogen 14 (stable)

After an organism dies, the C14 begins to decay into N14

= Carbon 14(radioactive)

= Nitrogen 14 (stable)

After an organism dies, the C14 begins to decay into N14

= Carbon 14(radioactive)

= Nitrogen 14 (stable)

After an organism dies, the C14 begins to decay into N14

= Carbon 14(radioactive)

= Nitrogen 14 (stable)

This decay happens at a constant rate– in 5730 years HALF of the C14 will have decayed into N14

= Carbon 14(radioactive)

= Nitrogen 14 (stable)

SO, AFTER 1 HALF LIFE—50% REMAINS

= Carbon 14(radioactive)

= Nitrogen 14 (stable)

THE DECAY CONTINUES--

= Carbon 14(radioactive)

= Nitrogen 14 (stable)

AFTER A 2ND HALF LIFE-THERE IS 25% REMAINING (50%25%)

= Carbon 14(radioactive)

= Nitrogen 14 (stable)

AFTER A 3RD HALF LIFE-THERE IS 12.5% REMAINING (25%12.5%)

Decay• 100%50% (1 half life)• 50%25% (2 half lives)• 25%12.5% (3 half lives)• 12.5%6.25% (4 half lives)• 6.25%3.125% (5 half lives)

Challenge Question: A bone is found to have 25% of its carbon-14 remaining. How old is it estimated to be?

2. Homologous structures

• Similar anatomical features that originated in a shared ancestor.

Prediction: if organisms shared common ancestors then we should find evidence of similar structures.

If time, explore the Zoo of You

3. Vestigial structures

• Structures that are useless to an organism but are similar to functional structures of related organisms or ancestors

Prediction: If new species develop from previously existing species then we should find evidence of features that are no longer used today, but were important in ancestors

4. Embryology

• The study of the early stages of development of an organism (inside the womb or inside the egg)

Prediction: If organisms shared common ancestors then we should find evidence that the embryologic structures develop in similar patterns.

If time, play Guess the Embryo

5. Comparing DNA and protein sequencesPrediction: If organisms shared common ancestors then we should find evidence of similar DNA sequences being used to build similar proteins. The more closely related two species are, the more similar their DNA.

1

9

14

18

21

Hypothesized relationship based on number of amino acid differences in cytochrome c

Family Trees (Phylogenetic Trees)• Are based on evidence, such as

homologous structures or DNA/proteins • Provide hypotheses about evolutionary

relationships: –how long since two species shared a

common ancestor (length of line)–How closely related two organisms are

(branching from common ancestor)

RHESUS MONKEY

KANGAROO

BULLFROG

TUNA

LAMPREY

TURTLE

Phylogenetic tree based on number of cytochrome c differences

1) WHICH 2 ORGANISMS SHOW THE CLOSEST RELATIONSHIP?

Human and Monkey- shortest branches

2) WHICH 2 ORGANISMS’ COMMON ANCESTOR LIVED THE LONGEST AGO?Tuna and Lamprey- longest lines

3) WHICH TWO ORGANISMS’ ANCESTOR LIVED MOST RECENTLY?

4) IF YOU DIDN’T KNOW WHAT KIND OF ANIMAL A LAMPREY IS, BASED ON THE TREE-WHAT KIND OF ANIMAL WOULD YOU PREDICT IT IS?Similar to a fish because it has a common ancestor with Tuna

5) COMPARE THE HUMAN-MONKEY RELATIONSHIP WITH THE HUMAN KANGAROO RELATIONSHIP.Human- monkey have more in common because of closer branches.Human- kangaroo have a common ancestor but less related because of longer lines.

6) WHY IS THE KANGAROO IN THE SAME GROUP AS THE HUMAN AND MONKEY-EVEN THOUGH THEY AREN’T AS CLOSELY RELATED?Common ancestor (both are mammals)

• Which pair of species has the fewest differences in their amino acid sequences for myoglobin (a protein)?

Green sea turtle

Logger head turtle

Map turtle

American alligator

Lace monitor lizard

• How does the relationship between green sea turtles and loggerhead turtles compare to the relationship between alligators and monitor lizards?

Green sea turtle

Logger head turtle

Map turtle

American alligator

Lace monitor lizard

Turtles closer related because shorter branches

Alligator and lizard have common ancestor but less related

Sketch a Phylogenetic Tree• A tiger and lion share have 5 differences in their

amino acid sequences for the protein Hemoglobin B. They share a common ancestor, which was cat-like.

• A hyena and a wolf have 18 differences in their amino acid sequences for Hemoglobin B. They share a common ancestor that was dog-like.

• Both cat-like creatures and dog-like creatures share a common ancestor (mammals with paws).

Draw a phylogenetic tree that illustrates this data. Be sure you pay attention to the distances that animals are from their common ancestors.