Bell Activity for Thursday, March 29, 2012

Bell Activity for Thursday, March 29, 2012

Take out your homework (Completed “Section Assessment” from page 561 and your defined vocabulary words for Chapter 21, sections 1-4) and place them on your desk in front of you.

Draw a bubble map with “How geological age is determined” in the center, and all of the ways that you know how to find it in bubbles surrounding it.

Agenda for Wednesday, March 28• Discuss the Bell Activity and receive credit for completed

homework.• Learn about Fairy Stones• Review the completed “section assessment” that you finished

for homework.• Watch video on Carbon dating• Take notes on Chapt. 21, sections 3 and 4• Play either bingo or baseball with vocabulary words• Begin working on section assessments on pages 565 and 569.

What is not completed in class will be finished for homework.

Vocabulary Quiz tomorrow, Friday March 30.

• Don’t forget to study for your vocabulary quiz tomorrow

• The test on Chapter 21 will be on Monday, April 2.

Importance of radiometric dating:

• Rocks from several localities have been dated at more than 3 billion years

• Confirms the idea that geologic time is immense

Dating sedimentary strata using radiometric dating

Dating of minerals in ash bed and dyke indicates that the sedimentary layers of the Dakota Sandstone through to the Mesaverde Formation are between 160 and 60 million years old

Other Ways to Determine Age

• Naturally occurring materials, such as trees, lake-bottom sediment, and volcanic ash can be used to help geologists find the age of objects or events.

Absolute-Age Dating of Rocks

Other Ways to Determine AgeTree Rings


– Age of tree determined by counting the number of annual tree rings in a cross section of the tree.

– The widths of tree rings are directly related to the climatic conditions during growth.

– Dendrochronology is the science of comparing annual growth rings in trees to date events and changes in past environments.

Other Ways to Determine AgeSeasonal Climatic Changes


– ~ 11 000 years ago glaciers covered northern United States.

– Varves are bands of alternating light- and dark-colored sediments of sand, clay, and silt found in lakes that resulted from summer and winter runoff from glaciers.

– Varves can be compared to find the ages of glacial lake

sediments from ~15 000 to 12 000 years ago.

Other Ways to Determine AgeDistinctive Sediment Layers


– Widespread sediment layer formed by instantaneous or short-lived event (volcanic ash).

– A key bed is a layer which has been dated and acts as a time marker, can be used to correlate rock layers across large areas.

Section Assessment1. Match the following terms with their definitions.

___ half-life___ dendrochronology___ varve___ key bed


A. alternating light- and dark-colored sedimentary deposits in glacial lakes

B. the time period until the ratio of parent-to-daughter atoms is equal

C. a widespread layer that has been accurately dated

D. the science of comparing annual growth rings in trees to date events and environmental changes

BDAC

Section Assessment2. How old is an object of organic origin if it has

25 percent of carbon-14 remaining? Why?


The object is 11 460 years old. To reach the 25 percent level, the carbon-14 has experienced 2 half-life cycles of 5730 years each.

Section AssessmentAbsolute-Age Dating of Rocks

3. Why would rubidium-87 with a half-life of 48.6 billion years probably not be useful in dating an object that is 100 000 years old?

With such a long half-life, the ratio of parent-to-daughter atoms would be too small to measure.

End of Presentation on Chapter 21, Section 3

Chapter 21, section 4Remains of Organisms in Rock Record

• Fossils are the evidence or remains of once-living plants or animals.

Remains of Organisms in the Rock Record

• Fossil record provides evidence of evolution. • Evolution is an adaptive change in the DNA of

populations as a result of mutation and/or environmental change.

• Fossils provide information about past environmental conditions, used to correlate rock layers from one area to another.

Note that each fossil has its own range of occurrence, and so strata of a particular age can be recognized from its fossils

Types of Fossils• Fossils with original preservation are the soft and hard

parts of plant and animal remains that have not undergone any kind of change since the organisms’ deaths.


• Uncommon, requires extraordinary circumstances like freezing, drying out, or oxygen-free environments.

Types of FossilsAltered Hard Parts


– Altered hard parts are fossils in which all the organic material has been removed and the hard parts of a plant or animal have been changed either by mineral replacement or by recrystallization.

– Permineralization is the process by which pore spaces in a fossil are filled in with mineral substances.

– exterior of the shell or a bone remains same, but shell & microstructures destroyed.

Types of FossilsIndex Fossils


– Index fossils are remains of plants or animals that can be used by geologists to correlate rock layers over large geographic areas or to date a particular rock layer.

– Index fossil is easily recognized, abundant, widely distributed, & must have lived briefly

Types of FossilsMolds and Casts


– A mold is formed when the original shell parts of an organism within a sedimentary rock are weathered and eroded.

– A cast of an organism is created if the cavity later becomes filled with minerals or sediment.

Types of FossilsIndirect Evidence of Past Life


– Trace fossils are indirect evidence of plant and animal life.

– Provide information about how an organism lived, moved, or obtained food.

Why study fossils?

• Help scientists interpret and describe Earth’s history.


• Help scientists find patterns and cycles used to predict future phenomena, such as climatic changes.

• Allow geologists to locate energy resources.

Section Assessment1. Match the following terms with their definitions.

___ original preservation___ altered hard part___ permineralization___ cast


A. fossils in which all organic material has been removed and bones or shells have been structurally changed

B. process by which pore spaces are filled in with mineral substances

C. fossils in which soft and hard parts of an organism have not undergone any kind of change

D. formed when a mold becomes filled with minerals or sediments

C

ABD

Section Assessment2. What conditions are necessary to allow original

preservation?


Original preservation requires extraordinary circumstances such as freezing, drying out, or oxygen-free environments.

Section AssessmentRemains of Organisms in the Rock Record

3. How might petroleum geologists use fossils?

Petroleum geologists use certain index microfossils to determine whether oil might be present at a particular site. These fossils provide information about the ages of rocks and, in some cases, information that indicates whether the temperature and pressure conditions needed to form oil or gas were present in those layers.

Documents

Bell Activity for Thursday, March 29, 2012