The Fossil Record

Evidence of Evolution 1. Much of the evidence that is used to support the idea that organisms have changed over time is the fossil record.

fossils 2. A fossil is the preserved remains of an ancient organism. It could be a part of the organism (a bone or tooth) or an imprint, such as a footprint.

sedimentary rock 3. Most fossils form in sedimentary rock. Over time, layers of particles build up. The weight of the layers causes the lower layers to turn into rock. If conditions are right, the remains of organisms are preserved within the rock. Many years later, weathering and erosion leave fossils exposed or near the surface.

sedimentary rock

Relative vs. Absolute Dating

4. One method of determining a fossil’s age compares fossils and rock layers. If the rock is unchanged, layers at the bottom were formed before the layers at the top. Therefore fossils in lower layers are older than fossils in higher layers.

Relative Dating 5. This comparison of the ages of different fossils based on the rock layer in which it was found is called relative dating. It is useful, but it does not tell the exact age of a fossil.

Relative Dating 6. Performed by estimating fossil age compared with that of other fossils.

Relative Dating The deeper it is, the older it is. Drawback – provides no information about age in years

Absolute Dating 7. Can determine the absolute age in years It is performed by radioactive dating – based on the amount of remaining radioactive isotopes. mya=million years ago

Absolute Dating Drawback - part of the fossil is destroyed during the test mya=million years ago

8. Paleontologists work to group the fossils of similar organisms together. They also arrange fossils in the order in which they lived.

Evidence of Evolution 9. The most complete fossil record we have is of the horse.

fossil record

10. The fossil record is an ordered arrangement of fossils 10. The fossil record is an ordered arrangement of fossils. It shows that most of the species that ever existed on Earth are now extinct.

11. Huge gaps in the record leave the explanation open to interpretation. Some scientists believe that the explanation for the gaps are from periods during which fossils were unable to form. 12. Other scientists believe the gaps show that the explanation of evolution is incorrect.

What could cause evolution to begin? geographic changes or barriers drought floods temperature changes loss or gain of a food source loss or gain of a predator pollution