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8/17/2019 Earthsciencechapter3!4!101209125156 Phpapp01

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Earth Science 3.4

Looking at Fossils


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1. Describe fve ways that dierent types oossils orm.

2. List three types o ossils that are not

part o organisms.3. Explain how ossils can be sed to

determine the history o changes inenvironments and organisms.

4. Explain how inde! ossils can be sed todate rock layers.

"b#ectives$


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Fossil

The trace or remains of an organism that livedlong ago, most commonly preserved insedimentary rock.%ost oten preserved in sedimentary rock& bt other

materials can also preserve evidence o past lie.

Fossils in Rocks

'hen an organism dies& it either begins to decayor is consmed by other organisms. Sometimes

dead organisms are (ickly bried by sediment&which slows down decay.Shells and bones are more resistant to decay than sot

tisses& so when sediments become rock& the harderstrctres are more commonly preserved.

Fossilized Organisms


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Fossils in Amber "rganisms occasionally become trapped in sot&

sticky tree sap& which hardens and becomes amber.

)nsect ossils have oten been preserved in this way&bt rogs and li*ards have also been ond in amber.

Petrifaction

+rocess in which minerals replace and organism,s

tisses.Permineralization+rocess in which the pore space in an organism,s hard

tisse is flled p with mineral.

Replacement +rocess in which an organism,s tisses are completely

replaced by minerals.


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Fossils in Asphalt -here are places where asphalt wells p at the

Earth,s srace. -hese thick& sticky pools can trap

and preserve organisms.

Frozen FossilsSince cold temperatres slow down decay& many

types o ossils have been ond preserved in ice.


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Trace Fossils

atrally preserved evidence o animal activityE!amples$+reserved animal tracks+reserved brrows or shelters that were made by animalsCoprolite, which is preserved animal dng.

olds and !asts are two more e!amples oossils.old mark or cavity made in a sedimentary srace by a shell or

other body.

!ast

type o ossil that orms when sediments fll the cavity letby a decomposed organism.

Other T"pes o# Fossils


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The $n#ormation in the Fossil %ecord

"ers only a rogh sketch o the history o lie on Earth.)ncomplete becase most organisms never became

ossils.Scientists know more inormation abot organisms that had

hard body parts and that lived in environments that

avored ossili*ation.

&istor" o# En'ironmental !hanges -he ossil record reveals changes in an area,s climate

over time.

/y sing the ossils o plants and land animals& scientists canreconstrct past climates.

&istor" o# !hanging Organisms/y stdying the relationships between ossils& scientists

can interpret how lie has changed over time.

(sing Fossils to $nterpret the )ast


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Scientists have learned that particlar types oossils appear only in certain layers o rock.

/y dating the rock layers above and belowthese ossils

Scientists can determine the time span in which theorganisms that ormed the ossils lived.

) a type o organism e!isted or only a shortperiod o time& its ossils wold show p in a

limited range o rock layers. -hese ossils are called inde! ossils.

$ndex #ossils Fond in the rock layers o only one geologic age& and

can be sed to establish the age o the rock layers.

(sing Fossils to Date %oc*s


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Ammonites Tropites& a marine mollsk similar to a modern

s(id& lived between 031 million and 012 millionyears ago.

TrilobitesFossils o a gens o trilobites called Phacops are

another e!ample o an inde! ossil. -rilobites are e!tinct and lived appro!imately 411

million years ago.'hen scientists fnd Phacops in a rock& they assme

that the rock is appro!imately 411 million years old.

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