T5 Fossils & the Rock Records

...it’s as old as the hills.PowerPoint Notes created by S. Koziol

Date : 12/1/2013 Revised : ?/?/??

Part 1 Objectives

• Describe the geological time scale• Distinguish among the following time

scale divisions: eon, era, period & epoch.

Time Scale

The geologic time scale divides Earth’s history into units from its origin to the present.

Era Period Epoch Began (MYA)

Cenozoic

Quaternary

Holocene 0.011

Pleistocene 1.8

Tertiary

Pliocene 5.3

Miocene 23.8

Oligocene 33.7

Eocene 54.8

Paleocene 65

MesozoicCretaceous 144

Jurassic 206

Triassic 248

Paleozoic

Permian 290

Carboniferous Pennsylvanian 323

Carboniferous Mississippian 354

Devonian 417

Silurian 443

Ordovician 490

Cambrian 540

Precambrian time4600

Adapted from Modern Earth Science, 2002, Holt, Rinehart and Winston

Time Scale – To be Completed

Blank Time Scale

Time Scale Continued

Recent period

The most recent period is the Quaternary

EpochOn the geologic time scale, the smallest unit of

time is called an epoch - longer than an age and shorter than a period.

Phanerozoic Eon

The Phanerozoic Eon includes the Paleozoic, Mesozoic, and Cenozoic Eras

Eons

The Archean and Proterozoic are examples of eons

End of the Precambrian

The end of the Precambrian is marked by the appearance of organisms with hard parts.

Cloudina, the earliest known calcium carbonate

shell-bearing fossil.

Units of geologic time

Units of geologic time in order from shortest to longest

• epoch, period, era, eon

Era Period Epoch Began (MYA)

Cenozoic

Quaternary

Holocene 0.011

Pleistocene 1.8

Tertiary

Pliocene 5.3

Miocene 23.8

Oligocene 33.7

Eocene 54.8

Paleocene 65

Mesozoic

Cretaceous 144

Jurassic 206

Triassic 248

Paleozoic

Permian 290

Carboniferous Pennsylvanian 323

Carboniferous Mississippian 354

Devonian 417

Silurian 443

Ordovician 490

Cambrian 540

Precambrian time4600

Adapted from Modern Earth Science, 2002, Holt, Rinehart and Winston

PeriodsPeriods are defined

by the abundance or extinction of life-forms.

Eras vs. Periods

Erasare longer spans of time,

measured in hundreds of millions to billions of years. They are defined by differences in life-forms found in rocks.

Periodsare usually measured in terms

of tens of millions of years to hundreds of millions of years. They are defined by the life-forms that were abundant or became extinct during the time in which specific rocks were deposited.

Both are units of time on the geologic time scale.

Part 2 Objectives

• Apply the principles for determining relative age to interpret rock sequences.

• Describe an unconformity and how it formed within the rock record.

Oldest rock layerThe oldest rock layer in an undisturbed rock

sequence occurs at the bottom of the sequence

The Principle of Superposition

The principle of superposition states that, in an undisturbed sequence, the oldest rocks are at the bottom of the sequence and successive layers are younger than those below them.

Cross-cutting RelationshipsYou can use the principle of cross-cutting

relationships to infer that a fault or an intrusion is younger than the rock it cuts across.

CorrelationThe matching of rock layers from one

geographic area with those of another area is known as correlation.

Inferences and rock layers

Uniformitarianism

The principle of uniformitarianism states that the The principle of uniformitarianism states that the processes occurring today have been occurring processes occurring today have been occurring on Earth since it formed. However, the rate, on Earth since it formed. However, the rate, intensity, and scale with which these processes intensity, and scale with which these processes occur have changed.occur have changed.

UnconformityWhen part of the rock record is destroyed, the

erosional gap that forms is an unconformity.

Angular UnconformityThe gap in the rock record that occurs between

folded or uplifted rock layers and a sedimentary rock layer on top of them is called an angular unconformity.

Nonconformity

A buried erosional surface between a nonsedimentary rock and a sedimentary rock is called a nonconformity.

Part 3 Objectives

• Explain the several different methods used by scientists to determine absolute age.

• Describe how objects are dated by the use of certain radioactive elements.

• Explain how annual tree rings and glacial varves are used to date geological events.

½ LifeThe amount of time it takes for one-half of the original amount of

an isotope to decay is known as its half-life.

Half Lives for Radioactive Elements

½ Life Practice Sheet

Absolute datingRadiometric dating is used to determine the

absolute age of a rock

Key BedsA key bed contains distinctive material that

geologists can easily recognize in the rock record and use as a time marker.

Contrast relative-age dating and absolute-age dating.

Relative-age datingRelative-age dating places the

ages of rocks and the events that formed them in order, without exact dates. This is done by comparing one event with another or one rock with another rock.

Absolute-age datingIn contrast, absolute-age

dating determines the actual age of a rock, a fossil, or an object. This is done through radiometric dating, a process that determines the ratio of parent material to daughter product in a given sample of rock or fossil.

Part 4 Objectives

• Define fossil.• Explain several methods by which fossils

can be preserved.• Describe the characteristics of an index

fossil.• Discuss how fossils can be used to

interpret Earth’s past physical and environmental history.

Fossils Fossils are the remains or evidence of once-

living plants or animals. They provide clues about Earth’s past environmental conditions and evolutionary changes in organisms over time. They also help to correlate rock layers from one area to another.

Fossils (continued)

Fossil insects preserved in hardened tree sap are called amber.

Fossils (continued)

Molds, casts, coprolites, and petrified wood are all example of fossils

Fossils - original preservation

Mummified animals found in dry caves can be examples of fossils with original preservation.

Fossils - original preservation

Fossil insects can be found imbedded in amber, the hardened sap of prehistoric trees.

An insect imbedded in amber is an example of a fossil with original preservation.

Fossils (altered)

An example of a fossil with altered hard parts includes petrified wood

Trace Fossils

An example of a trace fossil includes worm trails.

PermineralizationIn the process of permineralization, pore spaces

within an organism’s shell are filled in with mineral substances.

Fossils - casts

A cast forms when the hollowed-out impression of a fossil organism becomes filled with minerals or sediment.

Fossils - molds

When the original parts of an organism in a sedimentary rock are weathered and eroded, a hollowed-out impression called a mold forms.

Index fossilsIndex fossils are useful to geologists if the fossils

have lived over a short period of time

Index vs. Trace Fossils

Index fossils are the remains of organisms

that can be used by geologists to correlate rock layers over large geographic areas or to date rock layers.

Trace fossils are not remains but indirect

evidence of organisms, such as imprints, trails, and burrows.

Both are similar in that they are types of fossils.

EvolutionThe adaptation of life-forms to changes in the environment is

known as evolution.

A process by which (generations of) organisms adapt to changes in their environments.