Modified from © Fall 2005, Pflugerville ISD, 8th Grade 8th Grade Science

© Fall 2005, Pflugerville ISD, 8th Grade “The present is the key to the past.” -James Hutton In your notebook, write down the quote listed at the top of this slide. What do you think it means?

© Fall 2005, Pflugerville ISD, 8th Grade “The present is the key to the past.” -James Hutton We study the past because if we don’t, we are doomed to repeat it. But how can studying the present help us understand earth’s history? What are some processes you can see today that also occurred millions of years ago?

© Fall 2005, Pflugerville ISD, 8th Grade Earth’s Story & Those Who Listened James Hutton “The present is the key to the past.” Father of modern geology

© Fall 2005, Pflugerville ISD, 8th Grade Earth’s Story & Those Who Listened When teammates wear uniforms, they all look the same, or UNIFORM! Uniformitarianism is the idea that the same geologic processes shaping the Earth today have been at work throughout Earth’s history.

© Fall 2005, Pflugerville ISD, 8th Grade Earth’s Story & Those Who Listened James Hutton Hutton’s views of a billion-year-old earth clashed with most scientists’ belief in catastrophism. What do you think catastrophism is? What does it sound like?

© Fall 2005, Pflugerville ISD, 8th Grade Earth’s Story & Those Who Listened Catastrophism is the idea that all geologic change happens very quickly What does the word catastrophic mean?

© Fall 2005, Pflugerville ISD, 8th Grade Earth’s Story & Those Who Listened These scientists used huge floods, eruptions and catastrophes to explain rapid geologic change

© Fall 2005, Pflugerville ISD, 8th Grade Earth’s Story & Those Who Listened Modern Geology Most scientists believe in a “happy-medium”. - MOST change is gradual (uniformitarianism). -SOME change is caused by sudden events (catastrophism).

© Fall 2005, Pflugerville ISD, 8th Grade How have places changed over time? website 10

© Fall 2005, Pflugerville ISD, 8th Grade So what EVIDENCE can we use for geologic changes over time? In your notebook, divide your page into 4 boxes (use your entire page!). Title each box with one of the following: 1.Fossils 2.Sedimentary Rock 3.Earth’s Surface Features 4.Climate History As we go through this section, we will add notes to this page! 11

© Fall 2005, Pflugerville ISD, 8th Grade What are Fossils? Fossils are the remains of ancient animals and plants. Fossils can also be traces or impressions of animals and plants. Most fossils are found in sedimentary layers. The sand, rocks and pebbles cover the plants and animals after their death. Trilobite – an extinct marine arthropod. An arthropod is an invertebrate animal having an exoskeleton, a segmented body, and jointed appendages.

© Fall 2005, Pflugerville ISD, 8th Grade What are Fossils? Over time more sand and rock cover the remains. The parts of the dead animal that do not easily decay become covered in the sediment. These parts, such as bones or teeth, became fossils. Mastodon – Ancient relative of the elephant that roamed North and Central America

© Fall 2005, Pflugerville ISD, 8th Grade What are Fossils? As an animal or plant decays, water and minerals seep into the bones and teeth and replace the original matter with a rock-like substance. Plesiosaur fossil – fossil of a marine reptile found in Kansas

© Fall 2005, Pflugerville ISD, 8th Grade How are fossils formed? Fossils are categorized by how they were formed. The most common types of fossils are body fossils, cast fossils, mold fossils, and trace fossils. Fossilized fern

© Fall 2005, Pflugerville ISD, 8th Grade How are fossils formed? Body fossils are created when all or part of animal becomes fossilized. This can occur in sedimentary rock but body fossils are also found in ice, tar pits, amber fluids such as pine tree sap, and mummified Insects preserved in tree sap.

© Fall 2005, Pflugerville ISD, 8th Grade How are fossils formed? Cast fossils are formed when the original organism is dissolved by ground water and replaced by the minerals contained in the water. Petrified wood is a good example of a cast fossil.

© Fall 2005, Pflugerville ISD, 8th Grade How are fossils formed? Mold fossils are created when the original organism is destroyed or dissolved and the space left by the organism is filled with sediment that hardens into a mold. Often mold fossils are formed from shelled animals or animals with exoskeletons. This mold fossil includes several species of marine animals.

© Fall 2005, Pflugerville ISD, 8th Grade How are fossils formed? Trace fossils are formed when sediment fills or covers trace evidence left by animals or plants. Trace fossils include animal burrows, dung, foot prints, and gnawed areas on trees and bones. Coprolite is dung (a.k.a. poop) that has been fossilized. Scientists can study an animal’s diet by studying this alligator coprolite.

© Fall 2005, Pflugerville ISD, 8th Grade Paleontologists are scientists that study fossils in order to understand both extinct and living organisms. A paleontologist leads a team of scientists during excavation of fossils. They then identify and reconstruct the animals to study. How are fossils studied? Fun fact: Ross from the show “Friends” was a paleontologist!

© Fall 2005, Pflugerville ISD, 8th Grade Fossils help scientists understand the movement of the tectonic plates. When fossils that are the same species are found on two continents, scientists can identify movement of the earth’s plates as the cause of the fossil placement. How are fossils studied? Finding similar species on different continents is used as proof of the theory that the continents have drifted apart over time.

© Fall 2005, Pflugerville ISD, 8th Grade In your notebook, on the page with the 4 boxes from yesterday, write down what EVIDENCE fossils give for earth’s history. 22