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The History of Life:

Origin of solarsystem andEarth

ProkaryotesAtmospheric oxygen

Hadean

Archaean

4

3

Proterozoic

Animals

MulticellulareukaryotesSingle-celledeukaryotes

2

1

Colonizationof land

Humans! The geologic record is divided into the Hadean, Archaean, Proterozoic, and Phanerozoic eons

! The Phanerozoic eon includes the last half billion years

! The Phanerozoic is divided into three eras: the Paleozoic, Mesozoic, and Cenozoic

! Major boundaries between eras correspond to major extinction events in the fossil record

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Key Events in Origin of Life:! Key events in

evolutionary history of life on Earth" life originated

3.5–4.0 bya

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Prokaryotes:! Prokaryotes dominated life

on Earth from 3.5–2.0 bya! Had ETC; chemiosmotic mechanism

for ATP synthesis

3.5 billion year old fossil of bacteria modern bacteria

chains of one-celledcyanobacteria

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Stromatolites:Fossilized mats of prokaryotes resemble modern microbial colonies

Lynn Margulis

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Oxygen atmosphere: age of oxygen! Oxygen begins to accumulate 2.7 bya

" reducing ® oxidizing atmosphere! evidence in banded iron in rocks = rusting! makes aerobic respiration possible

" photosynthetic bacteria (blue-green algae)

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First Eukaryotes:! Development of internal membranes

" create internal micro-environments" advantage: specialization = increase efficiency

! natural selection!

infolding of theplasma membrane

DNA

cell wall

plasmamembrane

Prokaryoticcell

Prokaryotic ancestor of eukaryotic

cells

Eukaryoticcell

endoplasmicreticulum (ER)

nuclear envelope

nucleus

plasma membrane

~2 bya

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Endosymbiosis:

Eukaryotic cellwith mitochondrion

internal membrane system aerobic bacterium mitochondrion

Endosymbiosis

! Evolution of eukaryotes" origin of mitochondria" engulfed aerobic bacteria, but

did not digest them" mutually beneficial relationship

! natural selection!

Ancestral eukaryotic cell

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mitochondrion

chloroplast

Eukaryotic cell withchloroplast & mitochondrion

Endosymbiosis

photosyntheticbacterium

Endosymbiosis:! Evolution of eukaryotes

" origin of chloroplasts" engulfed photosynthetic bacteria,

but did not digest them" mutually beneficial relationship

! natural selection!

Eukaryoticcell with

mitochondrion

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! Evidence" structural

! mitochondria & chloroplasts resemble bacterial structure

" genetic! mitochondria & chloroplasts

have their own circular DNA, like bacteria" functional

! mitochondria & chloroplasts move freely within the cell

! mitochondria & chloroplasts reproduce independently from the cell

Theory of Endosymbiosis:

Lynn Margulis

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Biologists Discover How Viruses Hijack Cell’s MachineryJan 12, 2017 WOW! Way Cool Stuff @UCSD

ucsdnews.ucsd.edu/.../biologists_discover_how_viruses_hijack_cells_machineryCould this be how multicellular organisms evolved? One existing theory, called “viral

eukaryogenesis,” suggests that the first eukaryotic cell was created when a large virus took over a bacterium. Eventually, the bacterium and virus formed a compound cell, in which the

virus evolved into the nucleus. “It may be too early to know if this particular virus is an intermediate step in the transition from bacteria and viruses to multicellular eukaryotes, but

this discovery could broaden knowledge about the origins of life as we know it,” said Pogliano.

Cryo-electron tomography shows how the bacterial cell is reorganized to resemble a more complicated plant or animal cell with a red nucleus-like compartment and ribosomes, the smaller light blue structures. The reproducing viruses appear with dark blue heads and pink tails. Image by Vorrapon Chaikeeratisak, Kanika Khanna, Axel Brilot, Katrina Nguyen

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! Diversification of Animals" within 10–20 million years most of the major phyla of

animals appear in fossil record

“Cambrian explosion” with a very long fusePaleozoic Era: Cambrian period

543 mya

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Cambrian Period• 543-490 mya

•Many animal phyla

• Trilobites and sponges

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Ordovician Period

• 490-443 mya

• Trilobites, mollusks,

crinoids, corals

•Colonization of land by diverse plants, fungi &

animals

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Silurian Period• 443-417 mya

• Fishes, coral reefs, plants

•Diversification of many vascular

land plants

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More diversity during age of reptiles than there is

now!

Mesozoic Era: Triassic & Jurassic period

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Commonancestor oflineages Aand B

Lineage ALineage B

†

†

†

†

†

†

3 24 1 0Millions of years ago

The rise and fall of groups of organisms reflect differences in speciation and extinction rates:• The history of life on Earth has seen

the rise and fall of many groups of organisms

• The rise and fall of groups depends on speciation and extinction rates within the group. The rise of a group of organisms occurs when more new species are produced than are lostto extinction.

Such changes in the fates of specieshas been due to large-scale processes such as plate tectonics,mass extinction & adaptive radiation

Species diversity of an evolutionary lineage will increase when more new member species originate than are lost to extinction. In this example, by 2 mya both Lineage A and B have given rise to four sp., and no sp. have become extinct. By time 0, Lineage A contains only one sp., while Lineage B contains eight sp.

Extinct (†).

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Plate Tectonics: Crustal plates float on lower fluid mantle! Tectonic plates

move slowly through the process of continental drift

! Oceanic and continental plates can collide, separate, or slide past each other

! Interactions between plates cause the formation of mountains and islands, and earthquakes

Formation of the supercontinent Pangaea about 250 million years ago had many effects:

" A deepening of ocean basins" A reduction in shallow water habitat" A colder and drier climate inland

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Continental Drift is an ongoing process:

Continental drift has many effects on living organisms:" A continent’s climate can change as it moves north or south" Separation of land masses can lead to allopatric speciation

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The distribution of fossils and living groups reflects the historic movement of continents:

" For example, the similarity of fossils in parts of South America and Africa is consistent with the idea that these continents were formerly attached

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Cambrian explosion

Diversity of life & periods of 5 Mass Extinction:

*The fossil record shows that most species that have ever lived are now extinct*Extinction can be caused by changes to a species’environment*At times, the rate of extinction has increased dramatically and caused a mass extinction*Mass extinction is the result of disruptive global environmental changes

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The Chicxulub impact crater in the Caribbean Sea near the Yucatan Peninsula of Mexico indicates an asteroid or comet struck the earth and changed conditions 65 million years ago. Dust clouds caused by the impact would have blocked sunlight and disturbed global climate.

Cretaceous extinction:

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Consequences of Mass Extinctions:! Mass extinction can alter ecological communities and the niches

available to organisms! It can take from 5 to 100 million years for diversity to recover following

a mass extinction! Mass extinctions can change the types of organisms found in

ecological communities" For example, the percentage of marine organisms that were

predators increased after the Permian and Cretaceous mass extinctions

! Lineages with novel and advantageous features can be lost during mass extinctions

! By eliminating so many species, mass extinctions can pave the way for adaptive radiations e.g., mammals replace dinosaur niche

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The fossil record shows that diversity of life has increased over the past 250 million yrs. (blue line). This increased is fueled by adaptive radiation.

Adaptive Radiations:the rapid evolution of diversely adapted species from a common ancestorAdaptive radiations may follow:• Mass extinctions(red line)• The evolution of novel

characteristics making them more adaptable to vacant niches

• The colonization of new regions where they face little competition from other species

Mass Extinction and Diversity of Life

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Worldwide Adaptive Radiations:! Mammals underwent an adaptive radiation after the

extinction of terrestrial dinosaurs ! The disappearance of dinosaurs (except birds) allowed for

the expansion of mammals in diversity and size! Other notable radiations include photosynthetic prokaryotes,

large predators in the Cambrian, land plants, insects, and tetrapods. All three radiations are major evolutionary innovations for living on land Ancestral

mammal

ANCESTRALCYNODONT

Monotremes(5 species)

Marsupials(324 species)

Eutherians(placentalmammals;5,010 species)

050100150200250Time (millions of years ago)

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! 125 mya mammals began to radiateout & fill niches

Early mammal evolution:

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Regional Adaptive Radiations:

Dubautia waialealae

Dubautia laxa

Dubautia scabra

Dubautia linearis

Argyroxiphiumsandwicense

HAWAII

MAUILANAI

MOLOKAI

KAUAI

1.3millionyears

0.4millionyears

3.7millionyears

OAHU

5.1millionyears

Close North Americanrelative, the tarweedCarlquistia muirii

! Can occur when organisms colonize new environments with little competition

! The Hawaiian Islands are one of the world’s great showcases of regional adaptive radiation

Molecular analysis indicates that these varied plants known as “silversword alliance” are all descended from an ancestral tarweed that arrived on the islands ~ 5mya from N. America. Members of the silversword alliance have since spread into different habitats and formed new species with different adaptations from island to island where they face very little competition.

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Chimpanzee infant

Chimpanzee fetus

Human fetus Human adult

Chimpanzee adult

Chimpanzee adult

Major changes in body form can result from changes in the sequences and regulation of developmental genes:Effects of Developmental Genes! Genes that program development

control the rate, timing, and spatial pattern of changes in an organism’s form as it develops into an adult

! Heterochrony is an evolutionary change in the rate or timing of developmental events

! It can have a significant impact on body shape

The contrasting shapes of human and chimpanzee skulls are the result of small changes in relative growth rates

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Classifying Life:! Molecular data

challenges 5 Kingdoms! Monera was too diverse

# 2 distinct lineages of prokaryotes! Protists are still too diverse

# not yet sorted out

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OLD SCHOOL CLASSIFICATION

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3 Domain system:! Domains = “Super” Kingdoms

" Bacteria" Archaea

! extremophiles = live in extreme environments# methanogens# halogens# thermophiles

" Eukarya! eukaryotes

# protists# fungi# plants# animals

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KingdomProtista

KingdomFungi

KingdomPlantae

KingdomAnimalia

KingdomArchaebacteria

KingdomBacteria

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Key events in life’s history:3.5 billion years

ago (bya):First prokaryotes

(single-celled)

1.8 bya:First eukaryotes(single-celled)

1.2 bya:First

multicellulareukaryotes

500 mya:Colonization

of land by fungi, plants, and animals

535–525 mya:Cambrian explosion

(great increase in diversityof animal forms)

Millions of years ago (mya)4,000 3,500 3,000 2,500 2,000 1,500 1,000 500

Present

*Turn the clock back 48 hours = Early Earth*Last 20 minutes = dinosaurs*Last 2 seconds = cell phones

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In the last 2 hours we sure have made a mess of things.