Warm Up 1/8/08Warm Up 1/8/081. An example of a geologic event that could be recorded

in rocks is ____.a. a lunar eclipse c. a civil warb. a volcanic eruption d. the occurrence of sun spots

2. Nicolaus Steno proposed the most basic principle of relative dating, the law of ____.a. gravity c. superpositionb. fossil succession d. correlation

3. If a layer of sandstone is in contact with a mass of granite that contains small pieces of the sandstone, which rock is older?a. Both are the same age.b. the granitec. the sandstoned. It is not possible to determine which rock is older from this information.

Answers: 1) b. 2) c. 3) c.Answers: 1) b. 2) c. 3) c.

Fossils: Evidence Fossils: Evidence of Past Lifeof Past LifeChapter 12, Section 2Chapter 12, Section 2

Fossil FormationFossil Formation Fossil –Fossil – the remains or traces of an organism the remains or traces of an organism

preserved from the geologic pastpreserved from the geologic past The type of fossil that is formed is determined The type of fossil that is formed is determined

by the conditions under which an organism by the conditions under which an organism died and how it was burieddied and how it was buried

Some remains of animals—such as teeth, Some remains of animals—such as teeth, bones, and shells—may not have been altered bones, and shells—may not have been altered hardly at all over time (unaltered remains)hardly at all over time (unaltered remains)

The remains of an organism are likely to be The remains of an organism are likely to be changed over time (altered remains)changed over time (altered remains)

Fossils often become petrified, mineral-rich Fossils often become petrified, mineral-rich water soaks into small cavities and pores of water soaks into small cavities and pores of the original organism, and replace the the original organism, and replace the original materialoriginal material

Molds and casts are another common Molds and casts are another common type of fossil; it is created when a shell or type of fossil; it is created when a shell or other structure is buried under sediment other structure is buried under sediment and then dissolved by groundwaterand then dissolved by groundwater

Carbonization is effective in preserving Carbonization is effective in preserving leaves and delicate mineral forms, occurs leaves and delicate mineral forms, occurs when an organism is buried under fine when an organism is buried under fine sediment and subjected to pressures sediment and subjected to pressures which squeeze out its liquid and gaseswhich squeeze out its liquid and gases

Trace fossils are indirect evidence of Trace fossils are indirect evidence of prehistoric life (tracks, burrows, dung, prehistoric life (tracks, burrows, dung, etc.)etc.)

Two conditions are important for Two conditions are important for preservation: rapid burial and the preservation: rapid burial and the possession of hard partspossession of hard parts

Fossil FormationFossil Formation

Fossil TypesFossil Types

Concept CheckConcept Check

What are three types of fossils?What are three types of fossils? Petrified remains, molds, casts, Petrified remains, molds, casts,

impressions, and trace fossilsimpressions, and trace fossils

Fossils and CorrelationFossils and Correlation In the late 18In the late 18thth Century, William Smith found Century, William Smith found

that fossils were not randomly distributed that fossils were not randomly distributed throughout the rock layers, but each layer throughout the rock layers, but each layer contained a distinct assortment of fossils that contained a distinct assortment of fossils that did not occur in other layersdid not occur in other layers

The principle of fossil succession states that The principle of fossil succession states that fossil organisms succeed one another in a fossil organisms succeed one another in a definite and determinable order; any time definite and determinable order; any time period can be recognized by its fossil contentperiod can be recognized by its fossil content

Based on the rock record from around the Based on the rock record from around the world, geologists have identified an order of world, geologists have identified an order of fossils: an Age of Trilobites, an Age of Fishes, fossils: an Age of Trilobites, an Age of Fishes, an Age of Coal Swamps, an Age of Reptiles, an Age of Coal Swamps, an Age of Reptiles, and an Age of Mammalsand an Age of Mammals

Index Fossil –Index Fossil – a fossil that is associated a fossil that is associated with a particular span of geologic timewith a particular span of geologic time

Index fossils are widespread Index fossils are widespread geographically, are limited to a short geographically, are limited to a short span of geologic time, and occur in large span of geologic time, and occur in large numbersnumbers

Their presence provides an important Their presence provides an important method of matching rocks of the same method of matching rocks of the same ageage

Fossils can also be used to interpret and Fossils can also be used to interpret and describe ancient environmentsdescribe ancient environments

Fossils and CorrelationFossils and Correlation

Index FossilsIndex Fossils

AssignmentAssignment

Read Chapter 12, Section 2 (pg. 343-Read Chapter 12, Section 2 (pg. 343-346)346)

Do Section 12.2 Assessment #1-5 (pg. Do Section 12.2 Assessment #1-5 (pg. 346)346)