The History of Life

Chapter 17

Fossils Preserved traces and remains of ancient life.

The Fossil Record Paleontologists study ancient life through

fossils. They make inferences about past life and group similar

organisms together to create the fossil record. Fossils show that more than 99% of all living species

that have ever existed have become extinct.

How Fossils Form Is the fossil record complete?

Many more organisms die without leaving traces than those that do.

Most fossils form in sedimentary rock.

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

Interpreting Fossil Evidence Relative Dating –

Estimates a fossil’s age by comparing to other fossils present in the same layer. Index fossils identify a

particular era

Absolute (Radioactive) Dating – A more exact method of

determining a fossil’s age by determining the percent of a radioactive element left in the sample.

Relative Dating

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

Geologic Time Scale Represents evolutionary time. Precambrian time - before complex life Eras – after Precambrian time.

Paleozoic – fish and amphibiams Mesozoic – age of dinosaurs Cenozoic – age of mammals

Section 17-3

Geologic Time Scale with Key Events

Glaciations; mammals increased; humans

Mammals diversified; grasses

Aquatic reptiles diversified; flowering plants; mass

extinction

Dinosaurs diversified; birds

Dinosaurs; small mammals; cone-bearing plants

Reptiles diversified; seed plants; mass extinction

Reptiles; winged insects diversified; coal swamps

Fishes diversified; land vertebrates (primitive

amphibians)

Land plants; land animals (arthropods)

Aquatic arthropods; mollusks; vertebrates (jawless

fishes)

Marine invertebrates diversified; most animal phyla

evolvedAnaerobic, then photosynthetic prokaryotes; eukaryotes, then multicellular life

Cenozoic

Mesozoic

Paleozoic

PrecambrianTime

Quaternary

Tertiary

Cretaceous

Jurassic

Triassic

Permian

Carboniferous

Devonian

Silurian

Ordovician

Cambrian

1.8–present

65–1.8

145–65

208–145

245–208

290–245

363–290

410–363

440–410

505–440

544–505

650–544

Key EventsEra Period Time(millions of years ago)

Earth’s Early History Ancient earth was hostile.

Poisonous atmosphere ; no oxygen Oceans were a “hot thin soup” UV radiation, lightening, volcanos… So how did life begin?

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

Stanley Miller recreated early earth’s atmosphereMade simple organic molecules (amino acids…)

The first organic molecules…

Coacervates

Proteinoid microspheres may have formed in shallow pools as precursors to cells.

Evolution of RNA and DNA

Stromatolites Ancient prokaryotes added oxygen to the

atmosphere. The rise of oxygen caused drove some life

forms to extinction while others evolved.

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

Figure 17-12 Endosymbiotic TheoryEndosymbiotic Theory – origin of eukaryotic cells

This theory proposes that eukaryotic cells arose from symbiotic relationships between bacteria and cells.

Sexual Reproduction and Multicellularity

This ancient jellyfish was an early multicellular animal.

With the advent of sexual reproduction the rate of evolution took off.

Evolution of LifeEarly 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.

Heterotroph Hypothesis The first cells were…

Heterotrophs autotrophs Anaerobic aerobic Unicellular multicellular Asexual sexual

Patterns of Evolution Extinction

The last member of a species dies….(failure of a species to adapt)

Patterns of Evolution Adaptive radiation

An ancestral form evolves into diverse forms through natural selection

Patterns of Evolution Convergent evolution

Unrelated species evolve similar adaptations due to similar environments

Patterns of Evolution Coevolution -

Evolution of two different species in response to each other: symbiosis

Patterns of Evolution Gradualism –

A slow and steady rate of evolution

Patterns of Evolution Punctuated equilibrium –

Periods of rapid evolution followed by long stretches of stability

Section 17-4

Flowchart

that are

can undergo can undergo can undergo can undergo can undergo

in underunderform inin

Species

Unrelated Related

Inter-relationshiops

Similar environments

Intense environmental

pressure

Small population

s

Different environments

Coevolution Convergent evolution

ExtinctionPunctuate

d equilibrium

Adaptive radiation