Chapter 21 – Earth ’ s History 21.1 – The Rock Record

Chapter 21 – Earth’s Chapter 21 – Earth’s HistoryHistory

21.1 – The Rock Record21.1 – The Rock Record

Why study Earth’s history?Why study Earth’s history?

Scientists organize geologic time to Scientists organize geologic time to help them communicate about help them communicate about Earth’s history.Earth’s history.

Organizing TimeOrganizing Time

Fossils = the remains, traces, or Fossils = the remains, traces, or imprints of ancient organisms. imprints of ancient organisms.

By studying rock layers and the By studying rock layers and the fossils within them, geologists can fossils within them, geologists can reconstruct aspects of Earth’s history reconstruct aspects of Earth’s history and interpret ancient environmentsand interpret ancient environments

Geologic Time ScaleGeologic Time Scale

A record of Earth’s history from its A record of Earth’s history from its origin 4.6 billion years ago (bya) to origin 4.6 billion years ago (bya) to the present.the present.– The geologic time scale The geologic time scale enables enables

scientists to find relationships among scientists to find relationships among the geological events, environmental the geological events, environmental conditions, and fossilized life-formsconditions, and fossilized life-forms that that are preserved in the rock recordare preserved in the rock record

http://geology.com/time/geologic-time-scale-550.gif

Visualizing Geologic TimeVisualizing Geologic Time

Eons = is the largest of these time Eons = is the largest of these time units and encompasses the othersunits and encompasses the others– Divided into 4 different eons = Hadean, Divided into 4 different eons = Hadean,

Archean, Proterozoic, and PhanerozoicArchean, Proterozoic, and Phanerozoic– The three earliest eons make up 90 The three earliest eons make up 90

percent of geologic time, known percent of geologic time, known together as the Precambrian.together as the Precambrian. During the Precambrian, Earth was formed During the Precambrian, Earth was formed

and became hospitable to modern life. and became hospitable to modern life.

Eons are further divided into erasEons are further divided into eras

ErasEras

Usually tens to hundreds of Usually tens to hundreds of millions of years in duration.millions of years in duration.– Divided into 4 different eras = Divided into 4 different eras =

Precambrian, Paleozoic, Precambrian, Paleozoic, Mesozoic, CenozoicMesozoic, Cenozoic

Eras are divided into periodsEras are divided into periods

PeriodsPeriods

Tens of millions of years in Tens of millions of years in durationduration– Each period in the geologic Each period in the geologic

time scale contains epochs.time scale contains epochs. Epochs = hundreds of Epochs = hundreds of

thousands to millions of thousands to millions of years in durationyears in duration

http://www.habitat.adfg.state.ak.us/geninfo/kbrr/coolkbayinfo/kbec_cd/html/image/figures/geotime.gif

In-Class In-Class Assignment/HomeworkAssignment/Homework

Your Geologic Time ScaleYour Geologic Time Scale

21.1 – Notes 21.1 – Notes ContinuedContinued

Succession of Life-FormsSuccession of Life-Forms

Phanerozoic Phanerozoic Eon - Eon - multicellular multicellular life began to life began to diversifydiversify

Paleozoic Era - Paleozoic Era - the oceans the oceans became full of became full of many different many different kinds of kinds of organismsorganisms

http://www.palaeos.org/Paleozoic

Succession of Life-FormsSuccession of Life-Forms Trilobites = Small, Trilobites = Small,

segmented animals segmented animals among the first hard-among the first hard-shelled life-forms. shelled life-forms. – They dominated the They dominated the

oceans in the early oceans in the early part of the Paleozoic part of the Paleozoic Era. Era.

Land plants appeared Land plants appeared later, followed by later, followed by land animals. land animals.


End of the Paleozoic is marked by the End of the Paleozoic is marked by the largest mass extinction event in largest mass extinction event in Earth’s historyEarth’s history– In a mass extinction, many groups of In a mass extinction, many groups of

organisms disappear from the rock organisms disappear from the rock record at about the same timerecord at about the same time

– At the end of the Paleozoic, 90 percent At the end of the Paleozoic, 90 percent of all marine organisms became extinctof all marine organisms became extinct


Mesozoic Era is Mesozoic Era is known for the known for the emergence of emergence of dinosaursdinosaurs

Many other Many other organisms organisms appeared, appeared, including large including large predatory reptiles predatory reptiles and corals in the and corals in the oceansoceans

http://media-2.web.britannica.com/eb-media/50/8050-004-55077BBF.jpg


During the Mesozoic, water-dwelling During the Mesozoic, water-dwelling amphibians began adapting to amphibians began adapting to terrestrial environmentsterrestrial environments

Insects, some as large as birds, livedInsects, some as large as birds, lived Mammals evolved and began to Mammals evolved and began to

diversifydiversify Flowering plants and trees emergedFlowering plants and trees emerged


End of the Mesozoic is marked by a End of the Mesozoic is marked by a large extinction eventlarge extinction event

Many groups of organisms became Many groups of organisms became extinct, including the non-avian extinct, including the non-avian dinosaurs and large marine reptilesdinosaurs and large marine reptiles


Cenozoic Era - mammals increased Cenozoic Era - mammals increased both in number and diversityboth in number and diversity

Human ancestors, the first primates, Human ancestors, the first primates, emerged in the epoch called the emerged in the epoch called the Paleocene, and modern humans Paleocene, and modern humans appeared in the Pleistocene Epochappeared in the Pleistocene Epoch

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21.1 WKT (Transparency & Study 21.1 WKT (Transparency & Study Guide)Guide)

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Chapter 21 – Earth ’ s History 21.1 – The Rock Record