Unit 10: Fossils, Extinction, and Evolution
The record of life buried in rock, and the slow process, one generation at a time, that produced everything alive today.
4 topics · 13 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
How Fossils Form
- How it worksHow does a dead animal's body get buried in sediment and slowly turn to stone over millions of years?
- Common mistakeWhy isn't a fossil literally the animal's original bone, rather than a mineral copy of it?
- Going furtherWhat happens to the odds of fossilization for a soft-bodied jellyfish compared to a hard-shelled clam?
Your turn1 of 2
Why are fossils so incredibly rare when billions of animals have lived and died on Earth?What Fossils Tell Us
- How it worksHow do the layers of rock a fossil is found in tell scientists roughly how old it is?
- Worked exampleFind which fossil is older if it's found in a rock layer 50 meters below another fossil's layer, and lower layers formed first.
- Common mistakeWhy doesn't finding a fossil high on a mountain mean it was formed way up there?
Your turn1 of 2
Two fossils are found in rock layers 141 meters apart, with one directly below the other. Find how many meters below the upper fossil's layer the lower, older fossil sits.Extinction
- How it worksHow does a sudden change in environment leave species without the traits they need to survive it?
- Common mistakeWhy doesn't extinction only happen from sudden disasters like asteroids, rather than slow changes too?
- Going furtherWhat happens to the rest of an ecosystem's food web after one key species goes extinct?
Your turn1 of 2
Why did an asteroid strike wipe out the dinosaurs but leave small mammals and insects alive?Evolution: Change Over Generations
- How it worksHow does natural selection let individuals with helpful traits survive and pass those traits to more offspring?
- Common mistakeWhy doesn't an individual animal evolve during its own lifetime, only a population over many generations?
- Going furtherWhat happens to a population's traits over hundreds of generations if the environment keeps changing?
- Ties togetherHow does evolution by natural selection connect back to inherited traits and adaptations?
Your turn1 of 2
Why do finches on different islands end up with completely different shaped beaks after enough generations?