If index fossils are found in one group of rocks, then the rocks with these same fossils must be the same age EVEN IF THEY ARE FOUND REALLY FAR APART FROM EACH OTHER

Scientists classify organisms based on characteristics Key point #1: Scientists classify organisms based on characteristics

Classification Before Darwin: organisms were classified based on physical similarities and differences After Darwin: organisms were classified based on how recent their common ancestor is and how much DNA they have in common

Linnaeus Classification Linnaeus Classification Kingdom=King Phylum=Phillip Class=Came Order=Over Family=For Genus =good Species=soup

Key Point #2 When scientists want to classify an organism based on physical characteristics, they use a dichotomous key

Just like taking a quiz in a magazine! If you like comedies go to #3… If you like dramas go to #4…

To use a dichotomous key Begin with step 1a. Look at the organism you are classifying. If step 1a is true, do what this step tells you to do. If step 1a is NOT true go to step 1b. If step 1b is true, do what it says. Repeat this until you can name the organism

Let’s practice! Let’s go to 3! 1a. Tail fins are horizontal…………….. Go to 2 1b. Tail fins are vertical…………………Go to 3 Let’s go to 3!

Let’s practice! Let’s go to 5! 3a. Has gill slits behind mouth……………go to 5 3b. Has no gill slits………………………… Lepidosiren paradoxa Let’s go to 5!

Let’s practice! Sphyrna mokarran 5a. Head is hammer shaped………Sphyrna mokarran 5b. Tail fins are half the body lenth…Alopias vulpinus Sphyrna mokarran

Classification Before Darwin: organisms were classified based on physical similarities and differences After Darwin: organisms were classified based on how recent their common ancestor is and how much DNA they have in common

DNA ALL living things have DNA. There are only 4 possible nucleotides for ALL living things! The order of the nucleotides is what gives you different traits. Key Point #3: DNA supports evolution because the more DNA two organisms have in common, the more closely related they are.

SHARE A COMMON ANCESTOR!!!! Think about it! If organisms get DNA from their ancestors and they have similar DNA, it makes sense that they… SHARE A COMMON ANCESTOR!!!!

What percentage of her DNA does Ms. Clarke share with other organisms? 99.9% Duh!

What percentage of her DNA does Ms. Clarke share with other organisms? 98%

What percentage of her DNA does Ms. Clarke share with other organisms? 90%

What percentage of her DNA does Ms. Clarke share with other organisms? 30%

Key Point #1 A cladogram is a “tree of life” diagram that shows how organisms branched off from a common ancestor. The more recent the common ancestor, the more DNA they have in common!

How to read a cladogram Root= bottom of the cladogram, the common ancestor for all organisms in the cladogram Node: The last point where the species share a common ancestor Branch: The closer two organisms’ branches are, the more recently they separated into different species

Common ancestor

Whiteboards What organism is most closely related to the Caiman?

Whiteboards Tomistoma shares a close common ancestor with which two organisms?

Whiteboards Which organism is most closely related to primates?