Notebook Heading: Relative vs. Absolute Bellringer When throughout the year have we studied relative and absolute? What is the difference between the two?

How old is the Earth?

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 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 Carbon Films: an extremely thin coating of carbon on rock that forms when materials that make up an organism BECOME GASES AND ESCAPE LEAVING ONLY THE 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.

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.

Remember! A scientific theory is a well-tested concept that explains a wide range of observations. The fossil record shows that millions of types of organisms have evolved. However, many others became extinct.

Finding the Age of Rocks Through Rock Dating

ROCKROCK DATINGDATING

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: mya

Rock Joke!! What does a rock want to be when it grows up?

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 layers the oldest layer is at the bottom. Each higher layer is younger than the layers below it.

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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 THATN THE ROCK LAYERS AROUND IT AND 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.

Notebook Title Fossils Pt 2 List the layers from Youngest to Oldest.

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.

Relative Age Dating

Absolute-Age Dating The numerical age, in years, of a rock or object This has only been possible since the beginning of the twentieth century (1900’s) when radioactivity was discovered.

Radioactivity The release of energy from unstable atoms Read pages install install

The amount of time it takes for one half of the original amount of an isotope to decay is known as its HALF-LIFE.

Define the Following Terms: Fossilunconformity Catastrophismindex fossil Uniformitarianismisotope Carbon filmradioactive decay Paleontologisthalf life Relative ageabsolute age Superpositioninclusion

Relative and Absolute Age

Fossils in Louisiana?

Oldest Rocks found in Louisiana so far…82 million year old Cretaceous marine rocks!

On the basis of ostracods found within the marls and chalks exposed at the abandoned pit, the shark teeth appear to be about 66.4 to 74.5 million years old. This makes it the oldest vertebrate fossil found within Louisiana (Stringer and Henry 1996).

Oldest Marine Fossils Paleozoic marine invertebrates

Louisiana State Fossil – Palm Wood – 24 – 30 million years old

Largest Fossil – Basilosaurus about 60 feet long!

Primitive Eocene Whales (Basilosaurus cetoides)

Youngest Fossils – mammoths and snails 10,000 – 25,000 yrs

Avery Island Fossils suggest that early inhabitants of Avery Island shared the land with mastodons and mammoths, giant sloths, saber- toothed tigers and three-toed horses. The Hunt!

Study for your Wetlands Quiz! List and explain 2 points list 3 points explain how

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conditions and organisms on Earth change Catastrophism says that quickly. Uniformitarianism says that Earth is constantly being reshaped in slow, continuous cycles. 3–4. (in either order) The organism has hard parts, such as shells, bones, or teeth. The organism is buried quickly after it dies. 5–10. (in any order) Preserved remains are the actual remains of an organism. A carbon film forms when pressure drives off an organism’s gases and liquids. In mineral replacement, an exact copy of the organism is made when minerals fill spaces. Trace fossils are evidence of an organism’s activity, such as a footprint or tracks. A mold is the impression left in a rock of an organism. A cast of an organism forms when sediment or mineral deposits fill a mold. Catastrophism says that quickly. Uniformitarianism says that Earth is constantly being reshaped in slow, continuous cycles. The organism has hard parts, such as shells, bones, or teeth. The organism is buried quickly after it dies. Preserved remains are the actual remains of an organism. A carbon film forms when pressure drives off an organism’s gases and liquids. In mineral replacement, an exact copy of the organism is made when minerals fill spaces. Trace fossils are evidence of an organism’s activity, such as a footprint or tracks. A mold is the impression left in a rock of an organism. A cast of an organism forms when sediment or mineral deposits fill a mold.

What are Earth’s Processes?