Chapter 9 – 1 FOSSILS

Evidence of Ancient Life

Fossil are the preserved remains or traces of living things Fossil are the preserved remains or traces of living things. They form when living things die and are buried by sediment. They are usually found in _______________ rock

FOSSIL!

4Main Types of Fossils 2. Molds and Casts: 1. Petrified fossils: formed by replacement. Water carrying minerals replaces all or part of an organism. 2. Molds and Casts: Mold: hollow area in sediment in the shape of an organism Cast: water carrying minerals seeps into the mold and deposits the minerals

* 3. Carbon films: As a buried plant or animal decays, it releases gases containing carbon. The gases escape, leaving the carbon behind preserving the plant or animals image. *

* 4.Trace fossils: evidence that an organism was previously there and left evidence activity. Example: footprints, trails, burrows

Preserved Remains – processes that preserves the remains of organisms with little or no change to the organism. *Tar Pits *Amber *Freezing

Why do we study fossils? 1. The fossil record provides evidence about the history of life on Earth. The fossil record can tell us about past environments and climate change on Earth. The fossil record can tell us about mass extinctions.

* 2. The fossil record shows how organisms have changed over time. (evolution) It shows how organisms have gone from simple to more complex organisms.

Section 1 Review: 1. Describe the process by which most fossils are formed in rock. 2. What are the five types of fossils that can be found in rock? 3. How does the fossil record support the theory of evolution? 4. Describe one way in which the remains of an organism can be preserved. 5. Fossil seashells have been found in rock beds on land. What can you infer about how the area has changed?

Chapter 9 – 2 Finding the Relative Age of Rocks Rock layers provide a record of Earth’s geologic history.

Relative vs. Absolute Age of Rock Relative age is the age of a rock compared to the ages of other rocks. (Older or younger to other rocks). Geologists use the law of superposition to find a rock’s relative age. (OLDER ROCK LAYERS ARE AT THE BOTTOM-EACH LAYER ABOVE IS YOUNGER THAN THE ONE BELOW).

Absolute age refers to the actual number of years since the rock formed. Difficult to determine exactly.

Top of the Grand Canyon = youngest rock. Bottom of the canyon = oldest!

Other Clues to Relative Age Clues From Igneous Rock Other Clues to Relative Age Clues From Igneous Rock! Intrusion/Extrusion An extrusion is lava that cools and hardens on Earth’s surface (Extrusive Igneous Rock). Rock layers below an extrusion are older than the extrusion. An intrusion is magma that cools and hardens under Earth’s surface (Intrusive Igneous Rock). An intrusion is always younger than the rock above or below it.

Clues From Faults! A fault is a break in Earth’s crust. Forces inside the Earth cause movement of the rock on both sides of a fault. A fault is always younger than the rock it cuts through.

To determine the relative age of a fault, geologists find the relative age of the most recent rock layer through which the fault slices.

When a fault occurs it makes determining relative ages difficult as rock layers no longer line up. *

Gaps in the Geologic Record – No one’s fault! Folding and erosion cause unconformity as newer rock layers blend with older layers.

Using Fossils to Date Rocks Geologists use the relative age of rock layers to determine the age of the fossils within those layers.

TRILOBITES ARE INDEX FOSSILS! Index fossils are widely distributed and existed for a brief period of time. These fossils also give us clues to a rock layer’s relative age. Certain types of trilobites (large-eyed) existed after other trilobites became extinct.

Geologists can infer that large-eyed trilobites and the rock layers they were found in are younger than rocks at lower levels containing other types of trilobites. *

Define the following: Relative age Absolute age Law of superposition Extrusions Intrusions Unconformity Index fossil

Age of Rocks Relative age: the age a rock compared the age of surrounding rocks Absolute age: the age of a rock since it was formed Law of Superposition: in horizontal rock layers, the oldest is always on the bottom.

- unconformity: a gap in the geologic record * - extrusions: lava that hardens on the surface - always younger than the layer below it - intrusions: magma that hardens below ground - dike: always younger than the rock layer it cuts across - unconformity: a gap in the geologic record - missing layer(s) usually due to erosion

* -index fossil: a fossil that can be used to determine the relative age of rock layers - fossil must be widely distributed and should have existed for a short period of time. Fossils record shows how life has become more complex. Example : trilobites, ammonites

The Law of Superposition states that: A. rock layers are deposited horizontally. B. rock layers on the bottom are the oldest. C. rock layers on the top are the oldest. D. I don’t know

By studying fossils we can find out: A. when extinct organisms lived B. what extinct organisms behaved like C. the year they died D. I don’t know