How do scientists know evolution has occurred?

Evidence of the History of LIFE

Paleontologists: scientists who study fossilsGeologists: scientists who study rock layers

Who looks for the evidence?

Fossils can tell us Structure of an organismWhat the ateWhat ate themWhat 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

Fossil Evidence

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

Fossil Evidence cont’d

Where the age of a fossil is determined by comparing its placement with that of fossils in other layers of rockRock 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.

Relative Dating: “Law of Superposition”

Allows scientists to assign absolute ages to rocks.Radioactive elements decay into nonradioactive

elements at a steady rate, unique to that elementThis type of dating is measured in the half-life of

radioactive atoms (the length of time required for half of the sample to decay)

Radioactive Dating

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.

To Summarize…