What is Evolution? Unit 6: Seventh Grade

Theory vs. Fact Theory Fact An idea that has not been proven to be unequivocally true Examples: Big Bang The extinction of the dinosaurs An idea or truth that has been proven to be unequivocally true Examples: For every action, there is an equal and opposite reaction 6+6=12

Using these pictures, describe a frog:

Differences among Organisms As you can see, each frog has a different characteristic that might help the frog survive. An adaptation is a characteristic that helps an organism survive and reproduce in its environment. Look again at the picture --- what adaptations might the frogs have to survive their environment?

Adaptations May be: Physical –something an organism has Long neck to reach food Long legs to run faster Behavioral – something an animal does Nocturnal Burrows

Species A species is a group of living things that can mate with one another and produce fertile offspring. Groups of individuals of the same species living in the same place make up a population.

Do species change over time? Scientists think that the Earth has changed a great deal during its history, and that living things have adapted to the Earth’s changes and have changed as well. http://www.youtube.com/watch?v=dcUL_pB iPc0&safety_mode=true&persist_safety_mo de=1

For example, the most evil creatures EVER… snakes Before snakes slithered, they had limbs similar to those of lizards. To better adapt to their environment of small holes in the ground, they lost their legs. This allowed them to fit into a tighter space, in which they could hide from predators. This was true mostly for the first species of snakes, at a time when most reptiles didn't go above the ground for their prey but burrowed around in search of food. Modern boas and pythons actually still have a small stub where their legs used to be millions of years ago.

Scientists have observed that species have changed over time They have also observed that inherited characteristics in populations change over time. Scientists also think that as populations change over time, new species form. New species descend, or come from, older species. This process of populations changing over time is called evolution.

The Evidence of Evolution Evidence that organisms have changed over time is buried within the Earth’s crust. They layers are made of different kinds of rock and soil stacked up on top of each other.

Layer Upon Layer, Upon Layer …. These layers, form when sediments such as dust, sand or soil are deposited in an orderly fashion by wind, water and gravity. The Law of Superposition states that older layers are deposited before newer layers and are buried deeper within the Earth.

And under all those layers is evidence! And the evidence is the remains or imprints of once living organisms. These remains or imprints are called fossils. Fossils can be complete organisms, parts of organisms, or just a set of footprints.

The Fossil Record By studying these fossils, scientists have made a timeline called the fossil record. The fossil record organizes fossils by their estimated ages and physical similarities.

Evidence of Ancestry The fossil record is important in that it provides evidence about the order in which species have existed. The fossils found in newer layers of the Earth have more similarities to present day organisms. Fossils found in lower layers are less similar to present day organisms or may not exist anymore.

Common Ancestry From this evidence, scientists have observed that all living things have characteristics in common and inherit characteristics in similar ways. Scientists theorize that all living species have descended from common ancestors. Evidence of common ancestry can be found in fossils and in living organisms Evidence that groups of organisms have common ancestry can also be found by comparing their DNA

In conclusion When scientists compare common traits, fossil evidence and the DNA of organisms it supports the theory of common ancestry