Fossils and the Law of Superposition Terms to Know:

Warm Up March 7, 2013 During which time period did the first life forms exist and what were they like? Were mammals and dinosaurs ever on Earth at the same time? If so, When? Objectives: 8.L.4.1 -TSW understand the law of superposition as it pertains to relative age on the Geologic Time Scale. Essential Question: -How does the law of superposition help scientists identify where rocks and fossils belong on the Geologic Time Scale?

1-4 Which time periods do you think the following fossils were from? hadean eon archaen eon proterozoic eon paleozoic era mesozoic era cenozoic era none of the above 1. Insects 2. Bony Fish 4. Human 3. Dinosaur

Warm Up March 11. 2013 What is the difference between relative age and absolute age? How do scientists determine the relative ages of rocks and fossils? Describe one way in which scientists can determine the absolute age of a rock or fossil. Objectives: 8.L.4.1 -TSW understand the law of superposition as it pertains to relative age including index fossils and sedimentary rock layers. Essential Question: -How do rocks, fossils, and ice cores help scientists determine changes in Earth's past?

Warm Up 3/30/2017 What is an index fossil? How are index fossils used to determine the age of rocks and fossils? -------------------------BONUS-------------------------- Are Index fossils used to determine the absolute age or relative age of a rock or fossil? Objectives: 8.L.4.1 -TSW understand how the law of superposition can be used to determine the relative age of rocks and fossils. Essential Question: -How can scientists determine the relative age of rocks and fossils?

Herbetella Sinuata Herbetella sinuata. Articulate brachiopods were immobile suspension feeders. They are the most conspicuous group of fossils in Ordovician rocks and provide important index fossils.

A Trip Through Geologic Time

Fossils Fossils are preserved remains or traces of living things. Most fossils form when living things die and are buried by sediments. The sediments slowly harden into rock and preserve the shape of the organisms. Scientists who study fossils are paleontologists. Fossils

Fossils Fossils are usually found in sedimentary rocks. When an organism dies, its soft parts often decay quickly leaving only the hard parts to fossilize. Ex. Bones, Shells, Teeth, or Seeds

Kinds of Fossils Petrified Fossils: fossils in which minerals replace all or part of the organism. Ex: petrified wood When the object is buried by sediment, water rich in minerals seeps into the cells. After the water evaporates, hardened minerals are left behind.

Kinds of Fossils Molds and Casts A mold is a hollow area in sediment in the shape of an organism or part of an organism. A cast is a copy of the shape of an organism.

Kinds of Fossils Carbonized Films: an extremely thin coating of carbon on rock that forms when materials that make up an organism become gases and escape leaving only carbon behind. Trace Fossils provide evidence of the activities of ancient organisms. Ex: footprints, animal trails, or animal burrows.

Kinds of Fossils Preserved Remains are formed when an organism is preserved with little or no change. For example when organisms become preserved in tar, amber (tree sap), and freezing.

CARBONIZED FILMS FERN FOSSIL This carbon-film fossil of a fern is more than 300 million years old. All living things contain an element called carbon. When an organism dies and is buried in sediment, the materials that make up the organism break down. Eventually, only carbon remains. The thin layer of carbon left behind can show an organism’s delicate parts, like leaves on a plant.

Why Study Fossils? Scientists study fossils to learn what past life forms were like. Paleontologists classify organisms in the order in which they lived. All the information scientists have gathered is called the fossil record.

Fossil Record The fossil record provides evidence about the history of life on Earth. The fossil record also shows how different groups of organisms have changed over time. It also provides evidence to support the theory of evolution.

The fossil record shows that millions of types of organisms have evolved. However, many others became extinct. Over 99% of all organisms that ever existed on our planet are now extinct. Less than 1% mains!!! Remember!

Finding the Age of Rocks Through Rock Dating Radioactive decay

Ages of Rocks The relative age of a rock is its age compared to other rocks. Use words like: “older or younger” The absolute age of a rock is the number of years since the rock was formed. Ex: 358-360 mya

The Position of Rock Layers It can be difficult to determine a rocks absolute age. So… scientists use the law of superposition. According to the law of superposition, in horizontal sedimentary rock the oldest layer is at the bottom. Each higher layer is younger than the layers below it.

Other Clues to Relative Age Clues From Igneous Rock Lava that cools at the surface is called an extrusion. Rock below an extrusion is always older. Magma that cools beneath the surface is called an intrusion. An intrusion is always younger than the rock layers around an beneath it.

Other Clues to Relative Age Faults (a break in the rock) are always younger than the rock it cuts through! Unconformities: An unconformity is a gap in the geological record that can occur when erosion wears away rock layers and other rock layers form on top of the eroded surface.

Using Fossils to Date Rocks! Scientists use index fossils to match rock layers. An index fossil must be widely distributed and represent a type of organism that existed only briefly. They are useful because they tell the relative ages of the rock layers they are found in.

The Trilobite One example of an index fossil is a trilobite. Trilobites were a group of hard-shelled animals whose bodies had three distinct parts. They evolved in shallow seas more than 500 million years ago.

Reflection Questions What can you tell from undisturbed layers of sedimentary rock? Use the word relative age in your answer. How can index fossils be used to determine the ages of rock layers? What property of radioactive elements can make them useful for determining absolute age? What are two things in your life for which you know only their relative ages? A scientist finds the bones of a dinosaur. What could help the scientist determine the approximate age of the dinosaur bones? 6. Why are ice cores important to the study of geologic history?

7. What are transitional fossils and what theory do they best support? a) the theory of biological evolution b) the law of superposition c) the theory of geological evolution d) the theory of continental drift 8. Scientists find dinosaur fossils in the bottom rock layers of a cliff and mammal fossils in the middle rock layer of a cliff. What could best be concluded from this evidence? 9. In what ways is the movie, "Jurassic Park" a false representation of when dinosaurs roamed Earth? 10. Whether a fossil formed before or after another fossil is described by its: a) absolute age b) relative age c) fossil record