CHAPTER 14:EARTH’S HISTORY

Earth’s History

• Earth’s history is long and fascinating. • There have been great biological and

geological changes

Fossil Records

• The fossil record provides strong evidence of the evolution of life

Triceratops

Nicholas Steno

• Earth’s history has been unveiled by scientists applying the tools of critical thinking

• Nicholas Steno was a Danish theologian• First to suggest that fossils had once been living organisms• Developed the Principles of Original Horizontality, Superposition, and Lateral Continuity

James Hutton

• Scottish naturalist and physician• Father of geologic time• Proposed that geologic time was

indefinitely long• Believed the Earth was self-renewing

(basis of rock cycle)• Formulated the principle of

uniformitarianism

Charles Lyell

• British lawyer • Father of Modern Geology• Wrote Principles of Geology• Popularized Principle of Uniformitarianism• Developed the Principles of Cross-cutting

Relationships and Inclusions

Charles Darwin

• English naturalist and geologist • Studied Lyell’s Principles of Geology• Wrote On the Origin of Species by Means

of Natural Selection• Credited with the Theory of Evolution

Natural Selection

• All living things develop over time from a very few simple forms

All individuals survive equally

Conditions change and only well-

adapted individuals survive

New generation is dominated by well-adapted individuals

Can you think of a change in conditions that might lead

to natural selection?

Fossils

• Fossils are the remains of animals and plants, or traces of their presence, that have been preserved in the crust.

• Fossils preserve a record of past life.

How Are Fossils Made?

• Fossilization is the process that turns a once-living thing into a fossil.

• The Fossil record is biased. Rapid burial is required. In most cases just shell, teeth, and bones are preserved.

• Preservation is typically by: replacement or formation of a mold or cast.

Brachiopod shells

Are these molds or casts or both? Is there evidence of replacement here?

Rare, soft part preservation(dinosaur skin)

There are several lines of evidence for evolution

• Phylogeny

Phylogeny is the history of organismal lineages as they change through time. What are some of the changes evident in the phylogeny of the horse?

Homologous Structures

Vestigial Structures

How does the existence of vestigial

structures support the concept of

evolution?

Embryology

• Even distantly related organisms have similar embryonic forms that can be traced back to their evolutionary history

Molecular biology also provides evidence of evolution

• Changes within separate populations of the same species result in new species through natural selection.

• Genetic Mutation– (random changes to RNA or DNA)

• Genetic Variation– (differences in inherited traits)

Molecular biology documents the relationship of living organisms to their ancestors

Parasitic microbes, viruses, bacteria ... all evolve!

Extinctions

• Mass extinctions are dramatic events in the otherwise slow process of evolution

Which of the Phanerozoic extinctions had the greatest impact on marine organisms? Which one lead to the extinction of the terrestrial dinosaurs?

Extinction

• During a mass extinction large numbers of species die out within a relatively short period of time.

There are various hypotheses for each mass extinction ...

Geologic Time Scale

• The Geologic Time Scale is the “calendar” of events in Earth’s history

Geologic Column Drag and Drop Animation

Hadean Eon

• Heating of the interior• Magma “ocean”• “Iron Catastrophe” • Eventual cooling• Earliest crust and oceans• Ended ~ 3.8 bya • Began ~ 4.6 bya• Extraterrestrial barrage• Atmosphere rich in methane, ammonia and carbon dioxide

Why was the Earth so much hotter during the Hadean than it is now?

The Archean and Proterozoic Eons lasted from 3.8 million to 542 million years ago

Archean and Proterozoic cratons (i.e., continent crustal blocks)

Archean Eon

• Atmosphere noxious to modern organisms (methane, ammonia, carbon dioxide, and water vapor)

• More extraterrestrial bombardment• More volcanic outgassing• Continental Cratons form• Abundant life first appears (stromatolites)• Photosynthesis initiated

Ancient and modern stromatolites

The atmosphere of the Archean would have been noxious to us. What component of our atmosphere would have been noxious to the Archeans?

Proterozoic Eon

• Continents develop, clustered together (Rodinia) in the southern hemisphere• Mountain building• Atmosphere becomes gradually more oxygenated• Diversification of soft-bodied organisms

Phanerozoic Eon

• ~ 542 mya to present• Includes the Paleozoic, Mesozoic and Cenozoic eras• Major mountain-building events• Pangaea continues break up into modern continents• Complex life evolves with much diversification• Geographic separation isolates some populations• Punctuated by mass extinctions

Tiktaalik roseae - a critical transitional organism from Canada’s Arctic

In the Paleozoic Era complex life evolvedand the continents reorganized

The Cambrian Explosion

• Organisms that evolved during the Cambrian Explosion, developed some of the basic inherited traits that are still present today, and others that vanished forever.

What is so important about the fossils of the Burgess Shale in

the Canadian Rockies?St

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In the Mesozoic Era biological diversity increased and continents reorganized yet again

Mesozoic diversity

Allosaurus claw

Plesiosaur

Dicot leaf

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The Tethys Sea

• Continents separated and moved towards their present configuration. The Tethys Sea (the ancestor to the Pacific Ocean) wrapped the globe along the equator.

Tethys Sea

Mammals and birds diversified and primates arose during the Cenozoic Era

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(a) Sahelanthropus tchadensis (b) Australopithecus afarensis (c) Homo erectus (d) Homo sapiens sapiens

Earth in the Quaternary Period

Why was sea level relatively low during much of the Quaternary?

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