How do scientists know evolution has occurred?

Paleontologists: scientists who study fossils Geologists: scientists who study rock layers

Fossils can tell us Structure of an organism What the ate What ate them What environment they lived in All this information of past life groups organisms together by the order in which they lived (oldest to recent. This is called the FOSSIL RECORD. The fossil record can show how different groups of organisms changed over time

Life on Earth has changed over time, which is evident in the different fossils found in different rock layers

Where 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, with oldest at the bottom, and newest on top, closer to the surface. Paleontologists can also use index fossils to compare relative ages. To join the index, a species must be (1)easily recognized, (2)existed for a short period of time, but (3)had a wide geographic range.

Allows scientists to assign absolute ages to rocks. Radioactive elements decay into nonradioactive elements at a steady rate, unique to that element This type of dating is measured in the half-life of radioactive atoms (the length of time required for half of the sample to decay)

Relative dating estimates the age of a fossil by comparing it with other fossils, while radioactive dating is a precise calculation of the age of a sample based on the amount of remaining radioactive isotopes it contains.