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17–1 The Fossil RecordA. Fossils and Ancient Life

B. How Fossils Form

C. Interpreting Fossil Evidence

1. Relative Dating

2. Radioactive Dating

D. Geologic Time Scale

1. Eras

2. Periods

Section 17-1

Section Outline

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Relative Dating

Can determine

Is performed by

Drawbacks

Absolute Dating

Comparing Relative and Absolute Dating of Fossils

Section 17-1

Compare/Contrast Table

Imprecision and limitations of age data

Difficulty of radioassay laboratory methods

Comparing depth of a fossil’s source stratum to the position of a reference fossil or rock

Determining the relative amounts of a radioactive isotope and nonradioactive isotope in a specimen

Age of fossil with respect to another rock or fossil (that is, older or younger)

Age of a fossil in years

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Water carries small rock particles to lakes and seas.

Dead organisms are buried by layers of sediment, which forms new rock.

The preserved remains may later be discovered and studied.

Section 17-1

Figure 17-2 Formation of a Fossil

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Era Period Time

Permian

Carboniferous

Devonian

Silurian

Ordovician

Cambrian

(millions of years ago)Era Period Time

(millions of years ago)Era Period Time(millions of

years ago)

290 – 245

360–290

410–360

440–410

505–440

544–505

1.8–present

65–1.8

145–65

208–145

245–208

Quaternary

Tertiary

Cretaceous

Jurassic

Triassic

Vendian 650–544

Section 17-1

Figure 17-5 Geologic Time Scale

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Era Period Time

Permian

Carboniferous

Devonian

Silurian

Ordovician

Cambrian

(millions of years ago)Era Period Time

(millions of years ago)Era Period Time(millions of

years ago)

290 – 245

360–290

410–360

440–410

505–440

544–505

1.8–present

65–1.8

145–65

208–145

245–208

Quaternary

Tertiary

Cretaceous

Jurassic

Triassic

Vendian 650–544

Section 17-1

Figure 17-5 Geologic Time Scale

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Era Period Time

Permian

Carboniferous

Devonian

Silurian

Ordovician

Cambrian

(millions of years ago)Era Period Time

(millions of years ago)Era Period Time(millions of

years ago)

290 – 245

360–290

410–360

440–410

505–440

544–505

1.8–present

65–1.8

145–65

208–145

245–208

Quaternary

Tertiary

Cretaceous

Jurassic

Triassic

Vendian 650–544

Section 17-1

Figure 17-5 Geologic Time Scale

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Mystery Detective

Earth is billions of years old. There were not any witnesses to those early years. How, then, can scientists determine the conditions on Earth long before there were any scientists?

Think about how you draw conclusions about occurrences that you did not witness. If you saw the charred remains of a house, for example, you could infer that it burned down.

Section 17-2

Interest Grabber

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1. On a sheet of paper, list things that you can observe around you that lead you to infer about events you did not see. For example, what do skid marks in the roadway tell you?

2. Now, think about and list the evidence all around you that scientists might analyze when trying to piece together a history of Earth. How would finding the fossil of a sea animal in the middle of a desert tell a scientist something about the past?

Section 17-2

Interest Grabber continued

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17–2 Earth’s Early HistoryA. Formation of Earth

B. The First Organic Molecules

C. How Did Life Begin?

1. Formation of Microspheres

2. Evolution of RNA and DNA

D. Free Oxygen

E. Origin of Eukaryotic Cells

F. Sexual Reproduction and Multicellularity

Section 17-2

Section Outline

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Concept Map

Evolution of Life

Section 17-2

Early Earth was hot; atmosphere contained poisonous gases.

Earth cooled and oceans condensed.

Simple organic molecules may have formed in the oceans..

Small sequences of RNA may have formed and replicated.

First prokaryotes may have formed when RNA or DNA was enclosed in microspheres.

Later prokaryotes were photosynthetic and produced oxygen.

An oxygenated atmosphere capped by the ozone layer protected Earth.

First eukaryotes may have been communities of prokaryotes.

Multicellular eukaryotes evolved.

Sexual reproduction increased genetic variability, hastening evolution.

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Mixture of gases simulating atmospheres of early Earth

Spark simulating lightning storms

Condensation chamber

Cold water cools chamber, causing droplets to form

Water vapor

Liquid containing amino acids and other organic compounds

Section 17-2

Figure 17-8 Miller-Urey Experiment

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Aerobic bacteria

Ancient Prokaryotes

Ancient Anaerobic Prokaryote

Primitive Aerobic Eukaryote

Primitive Photosynthetic Eukaryote

Chloroplast

Photosynthetic bacteria

Nuclear envelope evolving Mitochondrion

Plants and plantlike protists

Animals, fungi, and non-plantlike protists

Section 17-2

Figure 17-12 Endosymbiotic Theory

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Team, Team, Team!

The first living things were unicellular. You, however, are multicellular. Is there an advantage to being multicellular?

Section 17-3

Interest Grabber

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1. Make a list of at least six different organs in your body, and next to each, write the main function of that organ.

2. Now, examine your list. Do any main functions overlap? Do two or more organs do exactly the same thing?

3. Use your list to jog your memory, and write down the functions that must be performed by a unicellular organism. For example, you may have written that your nerves help you sense your environment. Doesn’t a cell need to sense its environment, too?

Section 17-3

Interest Grabber continued