18 lecture ppt

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Biology

Sylvia S. Mader Michael Windelspecht

Chapter 18 Origin and History

of Life

Lecture Outline

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Outline

• 18.1 Origin of Life

• 18.2 History of Life

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18.1 Origin of Life

• The

last universal common ancestor

(LUCA)

is common to all organisms that

live, and have lived, on Earth since life

began.



Today, we say that “life only comes from life.”



However, the first cells had to arise from

nonliving chemicals.

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Origin of Life

• The Earth came into being about 4.6 BYA (BYA).

• The Earth’s mass provides a gravitational field strong

enough to hold an atmosphere

• Primitive Earth atmosphere:

 Most likely consisted of:

• Water vapor • Nitrogen

• Carbon dioxide

• Small amounts of hydrogen, methane, ammonia, hydrogen sulfide, and carbon monoxide

 Little free oxygen

 Originally too hot for liquid water to form

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Origin of Life

• Evolution of Monomers:



Several hypotheses suggest how monomers evolved

• Monomers came from outer space

– Comets and meteorites, perhaps carrying organic chemicals, have pelted the Earth throughout history.

– Organic molecules could have seeded the chemical origin of life on Earth.

– Bacterium-like cells could have been carried to Earth on a meteorite or comet.

• Monomers came from reactions in the atmosphere

– Oparin/Haldane Hypothesis (early 1900s)

» Suggested organic molecules could be formed in the presence of outside energy sources using atmospheric gases

• Monomers came from reactions at hydrothermal vents

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Origin of Life

• Stanley Miller (1953)



Conducted an experiment to test the Operin/Haldane

hypothesis

• Showed that gases (methane, ammonia, hydrogen, and water) can react with one another to produce small organic molecules (amino acids, organic acids).

• Strong energy sources



Rainfall would have washed organic compounds from

the atmosphere into the ocean



They would have accumulated in the ocean, making it

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Stanley Miller’s Experiment

7

electrode

cool water in hot water out stopcock for

withdrawing liquid stopcock for adding gases

boiler liquid droplets condenser

electric spark

CH₄ NH₃ H₂ H₂O

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Chemical Evolution at

Hydrothermal Vents

plume of hot water

rich in iron-nickel sulfides

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Origin of Life

• In cells, monomers join to form polymers

in the presence of enzymes



Iron-Sulfur World Hypothesis

• Suggests organic molecules reacted with amino acids to form peptides in the presence of iron-nickel sulfides:



Protein-First Hypothesis:

• Assumes that protein enzymes arose first • DNA genes came afterwards



RNA-First Hypothesis:

• Suggests only RNA was needed to progress toward formation of the first cell or cells

• DNA genes came afterwards

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Origin of Life

• Before the first true cell arose, there would have been a protocell or

protobiont, the hypothesized precursor to the first true cells.

• A protocell would have an outer membrane and carry on energy metabolism.

• Proteinoids are small polypeptides with catalytic properties.

• When proteinoids are placed in water, they form microspheres,

structures made of proteins with many properties of a cell

 If lipids are made available to microspheres, lipids become associated with microspheres, producing a lipid-protein membrane.

• Lipids placed into water form cell-sized double-layered bubbles

called liposomes.

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Comparison of Protocell and

Modern Cell Plasma Membranes

Protocell Membrane Cell Membrane

hydrophilic “head”

hydrophobic “tail”

phospholipid

outside cell outside protocell

inside protocell inside cell

phospholipid bilayer fatty acid bilayer

d. c.

a. b.

2 fatty acids

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Structure and Growth of the

First Plasma Membrane

.

b. a.

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13

Origin of Life

• Evolution of the

protocell



Nutrition

• The process would have had to carry on nutrition in

order to grow.

• If organic molecules formed in the atmosphere and

were carried into the ocean by rain, simple organic

molecules could have served as food.

– According to this hypothesis, the protocell was a heterotroph.

• If the protocell evolved at hydrothermal events, it

could have carried out chemosynthesis.

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Origin of Life

• Evolution of the

protocell

• Nutrition (continued)



Natural selection would have favored cells that could

extract energy from carbohydrates to produce ATP.

• Oxygen was not available.

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15

Origin of Life

• A Self-Replication System

 RNA-first hypothesis

• The first cell would have had RNA gene that directed protein synthesis

• Reverse transcription could have led to DNA genes

• RNA was responsible for both DNA and protein formation

• Eventually protein synthesis would have been carried out according to the central dogma, with information flowing from DNA to RNA to protein

 Protein-first hypothesis

• The protocell would have developed a plasma membrane and enzymes

• Then DNA and RNA synthesis would have been possible

• After DNA genes evolved, protein synthesis would have been carried out according to the central dogma

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Stages of the Origin of Life

x x x Stage 1 Stage 2 Stage 3 Stage 4 Stage 4 o lu tio n Bio lo g ic a l E v o lu tio n Bio lo g ic a l E v o lu tio n

Origin of Life: first self-replicating cell extinct lineages

Common ancestor of all life on Earth or LUCA (last universal common ancestor) extant organisms RNA DNA origin of genetic code proto cell plasma membrane polymers polymerization

Small organic molecules

cell cell

LUCA

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18.2 History of Life

• Fossils

- Remains and traces of past life

• Paleontology

is the study of the fossil record

• Most fossils are traces of organisms embedded

in

sediment



Sediment is produced by weathering and erosion of

rocks



Sediment becomes a recognizable

stratum

in the

stratigraphic sequence



Strata of the same age tend to contain the similar

fossil assemblages (

index fossils

) that can be used

for relative dating



This helps geologists determine relative dates of

embedded fossils despite upheavals (

relative dating

)

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The History of Life

a.

formation of Earth

oldest known rocks land plants

Age of Dinosaurs

11 1 10 2 2 3 3 4 4 5 5 6 6 7 7 8 9 10 9 12 midnight P.M. A.M. P.M. A.M. 8

first appearance of Homo sapiens (11:59:30) oldest multicellular fossils oldest eukaryotic fossils oldest fossils (prokaryotes) first photosynthetic organisms

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Fossils

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trilobite

fossil fern

placoderm

dinosaur footprint ichthyosaur

ammonites

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History of Life

• Absolute dating

assigns an actual date to a fossil

• One absolute dating method relies on

radiometric

(radioactive) dating techniques

• Half-life:

 The length of time required for half the atoms to change into

another stable element

 Unaffected by temperature, light, pressure, etc.

 All radioactive isotopes have a dependable half-life

• Some only fractions of a second • Some billions of years

• Most in between

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History of Life

• The

geologic timescale



divides the history of the earth into

• Eras • Periods • Epochs



Derives from accumulation of data from the age of

fossils in strata all over the world

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Geologic Timescale: Paleozoic

and Precambrian Eras

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History of Life

• The Precambrian includes about 87% of the geological

timescale

 Little or no atmospheric oxygen in the early atmosphere

 Lack of ozone shield allowed UV radiation to bombard Earth

• The first cells came into existence in aquatic

environments

 Prokaryotes

 Cyanobacteria fossils have been found in ancient stromatolites

 Photosynthetic cyanobacteria added oxygen to the atmosphere

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The Tree of Life

25

ARCHAEA

BACTERIA first cells

photosynthetic bacteria (produce oxygen) aerobic bacteria

other photosynthetic bacteria (do not produce oxygen) thermophiles

halophiles methanogens

mitochondria

chloroplasts

3.5 BYA 2.2 BYA 1.4 BYA 543 MYA

Archaebacteria Animals Fungi Protists Plants Bacteria 2 7 8 EUKARYA heterotrophic protists photosynthetic protists 1 3 4 5 6

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Prokaryote Fossil of the

Precambrian

0 20

10 mm

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History of Life

• Eukaryotic Cells Arise



About 2.1 BYA

• Most are aerobic

• Contain a nucleus as well as other membranous organelles



Endosymbiotic Theory

• Mitochondria were probably once free-living aerobic prokaryotes.

• Chloroplasts were probably once free-living photosynthetic prokaryotes.

• A nucleated cell probably engulfed these prokaryotes that became various organelles.



Cilia and flagella may have originated from slender

undulating prokaryotes that attached to the host cell.

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History of Life

• Support for the Endosymbiotic Theory



Mitochondria and chloroplasts are similar in size to

bacteria



Mitochondria and chloroplasts have their own DNA and

make some of their own proteins



Mitochondria and chloroplasts divide by binary fission



The outer membranes of mitochondria and

chloroplasts differ

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History of Life

• Multicellularity Arises



About 1.4 BYA



Separating germ cells from somatic cells may

have contributed to the diversity of organisms.



Early multicellular organisms lacked internal

organs and could have absorbed nutrients

from the sea.



It’s possible that they practiced sexual

reproduction

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Ediacaran Fossils

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History of Life

• The Paleozoic Era



Begins with the Cambrian Period



Lasted over 300 million years



Includes three major mass extinction events

• Disappearance of a large number of taxa

• Occurred within a relatively short time interval

(compared to geological time scale)

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History of Life

• The abundance of fossils of animals of the Cambrian

period may be due to the evolution of outer skeletons

• The ancestry of all modern animals can be traced to the

Cambrian period based on molecular clock data

• Molecular Clock:

 Based on hypothesis that

• Changes in base-pair sequences of certain DNA segments occur at a fixed rate, and

• The rate is not affected by natural selection or other external factors

 When these base-pair sequences are compared between two

species:

• Count the number of base-pair differences

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Sea Life of the Cambrian

Period

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Opabinia

Thaumaptilon Vauxia

Wiwaxia

(Opabina): © A. J. Copley/Visuals Unlimited; (Thaumaptilon): © Simon Conway Morris, University of Cambridge; (Wiwaxia): © Albert Copley/Visuals Unlimited; (Vauxia): © Alan Siruinikoff/Photo Researchers, Inc.

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History of Life

• Invasion of land



Plants

• Seedless vascular plants date back to the Silurian period • Later flourished in Carboniferous period



Invertebrates

• Arthropods were the first animals on land

• Outer skeleton and jointed appendages pre-adapted them to live on land



Vertebrates

• Fishes first appeared in the Ordovician period

• Amphibians first appeared in the Devonian period and diversified during the Carboniferous period

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Swamp Forests of the

Carboniferous Period

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a: © The Field Museum, #CSGEO75400c; b: © John Cancalosi/Peter Arnold, Inc.; c: © John Gerlach/Animals Animals/Earth Scenes; Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

a.

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History of Life

• The Mesozoic Era



Triassic Period

• Nonflowering seed plants became dominant



Jurassic Period

• Dinosaurs achieved enormous size

• Mammals remained small and insignificant



Cretaceous Period

• Dinosaurs declined at the end of the Cretaceous period due to a mass extinction

• Mammals:

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Dinosaurs of the Late

Cretaceous Period

37

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History of Life

• The Cenozoic Era



Mammals continued adaptive radiation



Flowering plants were already diverse and

(39)

Mammals of the Oligocene

Epoch

39

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Woolly Mammoth of the

Pleistocene Epoch

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18.3 Geological Factors That

Influence Evolution

• Continental drift



The positions of continents and oceans are

not fixed



Plate tectonics

• Earth’s crust consists of slab-like plates

• Tectonic plates float on a lower hot mantle layer

• Movements of plates results in continental drift

• Modern mammalian diversity results from

isolated evolution on separate continents

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Continental Drift

North America Eurasia South America Africa India Australia North America Eurasia Africa India Australia Antarctica South America Laurasia

(251 million years ago) (135 million years ago)

Antarctica Present day (65 million years ago)

PALEOZOIC MESOZOIC CENOZOIC

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Geological Factors that

Influence Evolution

• Mass extinctions occurred

at the end of the following

periods:

• Ordovician

 444 MYA

 75% of species disappeared

• Devonian

 360 MYA

 70% of marine invertebrates

disappeared

• Permian

 251 MYA

• Triassic

 20 MYA

• Cretaceous

 66 MYA

 75% of species

disappeared

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Mass Extinctions

ammonoids extinct poriferans brachiopods insects birds mammals 65.5 MYA

75% 70% 90% 60% 75%

poriferans brachiopods mammals birds dinosaurs insects ammonoids dinosaurs extinct

CAMBRIAN ORDOVICIAN SILURIAN DEVONIAN CARBONIFEROUS PERMIAN TRIASSIC JURASSIC CRETACEOUS TERTIARYQUARTE

-RNARY PRESENT 199.6 MYA 251 MYA 359.2 MYA Major Extinctions % Species Extinct 443.7 MYA STATUS TODAY