Evidence of Evolution

Random Fact of the Day Most people had brown eyes until about 10,000 years ago when a single genetic mutation from the Black Sea switched the eyes from brown to blue. Approximately 8% of the world’s population now has blue eyes

James Hutton First scientist to propose that the Earth was very very old (1788) Proposed that rocks, mountains, and valleys had been changed gradually by rain, heat, cold, the activity of volcanoes, and other natural events. He argued that the Earth had to be much more than a few thousand years old because these processes operate slowly.

Charles Lyell Lyell built on Hutton’s belief that the Earth had changed gradually over time by saying that these events must be observed if the scientific method could work. Other evidence that the Earth is constantly changing is the appearance of fossils in stone.

Geological Time Scale Layers of rock that correspond with different time periods. Relative dating is a way of determining the age of fossils relative to other fossils in different layers of rocks. This still did not tell scientists how old the fossils were, because they did not know how long it took for the layers to form. Radioactive Dating allows scientists to determine the actual age of rocks by looking at how much of the radioactive material has decayed. Different elements have different rates of decay (or half-lives)

Eg. Carbon dating AGE 0 100% 50% AGE 5730 yrs 25% AGE 11,460 yrs 12.5%

The Fossil Record Fossils have been formed in many ways: Animals were frozen in ice/snow Insects & small animals trapped in tree sap Animals became trapped in bogs, quick sand, or tar pits The material surrounding the organism protected it from decaying and acted to preserve it.

Incomplete Fossil Record Many organisms do not become fossils when they die. For every organism that leaves a fossil, many vanish without a trace The fossil record is incomplete Organisms in certain environments may never become a part of the fossil record (sedimentary rock) What other reasons may be causing the incomplete fossil record?

Finding fossils in tons of rock can be difficult Some organisms are very small Environments can be difficult to reach ???

What the Fossil Record Tells Us The probable relationship between organisms Major changes in the Earth’s climate and geography Fossil shark teeth in Arizona Giant fossil ferns in N. Am. The Earth is always changing

What vestigial organs do you know about? Structural Evidence Homologous structures: body structures that have different functions but come from the same body part Vestigial organs: organs that are so reduced in size and function that they are only traces of similar organs in other species What vestigial organs do you know about?

What Does Homology Mean? Tells us that all living things evolved from common ancestors Ties back to Darwin: “Living organisms evolved through gradual modification of earlier forms –descent from a common ancestor”