Chapter 17

Chapter 17

The History of Life

17-1 The Fossil Record

• Paleontologists- scientists who study fossils

• Fossil Record- all the information about past life forms.

– Provides evidence of the history of life on Earth.

– Shows how different groups of organisms have changed over time.

What the record shows

– Certain fossils appear only in certain rock layers

• Some older, some more recent

99% of all species on Earth are extinct

How fossils form

• Primarily found in sedimentary rock

• Hard parts- bones, wood, shells mineralize

• Soft parts- leave impressions

• The fossil record is selective and incomplete

Fossil Dating- Relative Dating

• Relative dating- the age of a fossil is determined by comparing its placement with that of fossils in other rock layers

• Index fossils- used in relative dating. Must be short lived and wide spread

Fossil Dating- Radioactive Dating

• Half-life- length of time for half of the radioactive atoms to decay

• Radioactive dating- calculating the age based on the amount of radioactive isotopes remaining.– Carbon 14, half-life of 5730 years (useful up to 60,000 years)

• Carbon 14 decays into Nitrogen-14

• The ratio of Carbon 12 to Carbon 14 is used

Potassium-40 decays into Argon-40, half-life of 1.26 billion years

Geologic Time Scale

Era Period Time (millions of years ago)

Cenozoic Quaternary 1.8 - present

Tertiary 65 - 1.8

Mesozoic Cretaceous 145 – 65

Jurassic 208 – 145

Triassic 245 – 208

Paleozoic Permian 290 – 245

Carboniferous 360 – 290

Devonian 410 – 360

Silurian 440 – 410

Ordovician 505 – 440

Cambrian 544 – 505

Precambrian Vendian 650 - 544

17-2 Earth’s Early History

• Earth- 4.6 billion years old

• Early Earth atmosphere- hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, sulfide, and water

• 4 billion years ago- solid rocks form

• 3.8 billion years- water in liquid form, oceans form

First Organic Molecules

• 1950s Stanley Miller and Harold Urey

– Simulated conditions of the early earth

Stanley Miller and Harold Urey

• Hydrogen, methane, ammonia and water combined with an electric spark

• Produced amino acids

The Puzzle of Life’s Origin

• After the Earth cooled 3.8 billions years ago, 200 to 300 million years later, bacteria form

• Proteinoid microspheres- tiny bubbles formed by organic molecules. Selectively permeable membranes

Evolution of RNA and DNA

• RNA probably preceded DNA

Free Oxygen

• Early Earth’s atmosphere had very little oxygen

• 3.5 Billion years ago- bacteria appear

• 2.2 Billion years ago- photosynthetic bacteria common

– Oxygen combined with iron in oceans

• Iron oxide formed and deposited in the oceans

Origin of Eukaryotic Cells

• 2 billion years ago- developed of organelles in prokaryotes

• Endosymbiotic theory- eukaryotic organisms arose from a mutalistic relationship between prokaryotes

Endosymbiotic theory-evidence

• Mitochondria and chloroplasts

– 1. contain DNA similar to bacterial DNA

– 2. have ribosomes similar to bacteria

– 3. reproduce by binary fission

17-3 Evolution of Multicellular Life

• Precambrian

– Anaerobic and aerobic bacteria appear

– -Eukaryotes appear

– Mulitcellular organisms appear

Era Period Time (millions of years

ago)Cenozoic Quaternary 1.8 - present

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Cambrian

• Cambrian Explosion

– Shells appear

– Invertebrates

• Jellyfish

• Worms

• Sponges

Arthropods



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Ordovician and Sulurian

• Octopi and squid

• Jawless vertebrates

• Plants on land

• Aquatic arthropods



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Devonian

• Ferns

• Insects

• Bony skeleton fishes

• Vertebrates on land



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Carboniferous and Permian

• Reptiles

• Winged insects

• 95% of organisms became extinct



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Triassic

• Age of Reptiles

Fish

Insects

Reptiles

Cone-bearing plants

Small mammals



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Jurassic

• Dinosaurs

• Archaeopteryx- first bird



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Cretaceous

• Dinosaurs

• Plants with seeds

• 50% of organisms became extinct



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Tertiary

• Earth warmed

• Mammal diversity

– Land

– Water

– Air



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Quaternary

• Series of ice ages and then warming

• Continued diversity of plants and animals

• 200,000 modern humans



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17-4 Patterns of Evolution

• Extinction

– Mass extinction causes

• Changing environment: sea levels change, temperature change, land masses move

• Accident- asteroid impact

Adaptive Radiation

• A single species evolves into many other diverse forms that live in different ways

– Example: Darwin’s finches

Convergent Evolution

• Process by which unrelated organisms resemble each other

• Organisms adapt to a similar environment in similar ways

Coevolution

• Process by which two species evolve in response to changes in each other over time

– Example- plants and pollinators

Punctuated Equilibrium

• Gradualism- slow change over time

• Equilibrium- no change

• Punctuated Equilibrium- long periods of no change combined with short periods of rapid change

– Rapid changes caused by:

• Small population

• Founders of a new colony

• New niches open after mass extinction

Development of Genes and Body Plans

• Hox genes- master control genes

– Changes in Hox genes have big effects on organisms

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Chapter 17