lec15+origin of life

7/27/2019 Lec15+Origin of Life

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The History of Life on Earth

When did life arise onEarth?

The Earth is thought to

be approximately 4.6billion years old, but life

is believed to have

occurred approximately 4

billion years ago (bya)

How did life begin???


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The Origin of Life: Early Ideas

Spontaneous Generation idea popular in the 1600-1700s

living things come from the nonliving

evidence: beetles and other insect larvae arise fromcow dung; frogs emerge from mud

In 1688, the Italian Francisco Redi In 1668,Francesco Redi, an Italian physician, did anexperiment with flies and wide-mouth jars. Hedemonstrated that meat that was covered did

not produce maggots

This may have been the first true scientificexperiment


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Francesco Redi experiment with

flies and wide-mouth jars


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The Origin of LifeSpontaneous generation

Mid-1800sdisproved by Louis Pasteur andJohn Tyndall

Broth in flask is boiled

to kill preexisting

microorganisms.

Condensing water collects

as the broth cools, sealing

the mouth of the flask.

If neck is later broken off,

outside air can carry

microorganisms into broth.

no growth growth


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Other Ideas: Life from aBiblical Creation?

Christian Creationism statesthat the world, including alllife, was created about 6,000years ago in six literal daysby a God.

But how does one accuratelyand fairly test for this?...

Whats the observation,

hypothesis, test?

This idea does not really fit intothe confines of a Science

course.

Like the study of French Impressionist

painters, Religion is not part of, nor

adequately covered in, a Science course.


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Origin of Life:Another idea


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Biogenic-looking features in

ALH84001 Martian meteorite

http://ares.jsc.nasa.gov/astrobiology/biomarkers/images.html


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In 1969, a meteorite (left-over bits from the origin of the

solar system) landed near Allende, Mexico. The AllendeMeteorite (and others of its sort) have been analyzedand found to contain amino acids, the building blocksof proteins.

This idea ofpanspermiahypothesized that life originatedout in space and came to earth inside a meteorite. Theamino acids recovered from meteorites are in a groupknown as exotics: they do not occur in the chemicalsystems of living things. The ET theory is nowdiscounted by most scientists, although the August1996 discovery of the Martian meteorite and its

possible fossils have revived thought of life elsewherein the Solar System.

Anyway.This only moves the problem to elsewhere!

Extra-terrestrial Origins


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The Lates t on Extra-terres tr ial

Origins

The Raelians Raelians believe that humanity

was created from the DNA of

superior alien scientists Follow the teachings of a

former French magazinesportswriter and wannabe

race-car driver ClaudeVorilhon, 56. He took thename "Rael" after he claimeda close encounter of the third

kind.


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Origin of Life: Current Theory

Chem ical Evo lut ion

.....The idea that long ago complex

collections of chemicals formed the first

cells.

Life began in the oceans 4 bya from

simple chemicals joining together in a

primordial soup

Complex chemicals evolved into living

cells


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What were the conditions like on Earth when life arose?

Up to about 4 bya, asteroid impacts and volcanic eruptions resulted

in the release of various gases that began to form an atmosphere

It consisted mainly of CO2, with some nitrogen, water vapor and

sulfur gases; hydrogen quickly escaped into space

CO2 in the atmosphere trapped solar radiation, making the Earths

surface rather warm

Earth was cool enough to form a crust, and water vapor condensed

to form oceans

Oceans in turn helped to dissolve CO2 from the atmosphere and

deposit it into carbonate rocks on the seafloor


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What were the conditions like on Earth when life

arose?

Organic molecules were undoubtedly beingformed on the Earths surface

Lightening and ultraviolet radiation from the Sun

acted on the atmosphere to forms small traces of

many different gases, including ammonia (NH3),

methane (CH4), carbon monoxide (CO) and ethane

Also, cyanide (HCN) probably formed easily in theupper atmosphere, from solar radiation and then

dissolved in raindrops


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The Origin of Life

The possible origin of

organic molecules

a. 1953theStanley Miller

experiment


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What is the simplest living cell that one can imagine?

A universal minimal cell

must contain the following::

Cell membrane

Cytoplasm DNA and RNA

Proteins

Enzymes

Ribozymes


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The Origin of LifeEarly Speculations

More circumstantial evidence

accumulated

Astronomers found simple organic

compounds in meteorites

They were convinced that Earths initialatmosphere could not have matched

Oparin-Haldanes model


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More circumstantial evidence

Fossils of ancient bacteria (3.5 billion years old)

were found in Australia

Suggested life may have evolved rapidly in less

than a billion years


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What are the possible scenarios?

When ocean tidal pool evaporates Salts get highly concentrated

Could have happened in ancientoceans

Concentrating aminos, may allow

protein to form


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Phospholipids arrange themselves into bubbles

Chemicals could be concentrated in bubbles (mightcontain protein, etc.)

These bubbles would persist aided by natural selection

If they burst, spew contents into air where otherreactions occur

Over hundreds of millions of years, similar processescould have filled oceans with proteins, carbohydrates,phospholipids, nucleotides

Th O i i f Lif


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Phospholipids arrange themselves intobubbles

Eventually they reach a level ofcomplexity

Called protocells (not living)

Still cant reproduce, no DNA

Th O i i f Lif


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Is DNA essential?

Scripps Institute, 1993 found smallmolecules of synthetic RNA that within an

hour began making copies of itself & the

copies made more copies

Then copies began to change - evolve-

acquiring new chemical characteristics,

but not alive


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Is DNA essential? Protocells might qualify as the first cells if they have

RNA that:

Can make copies of itself & evolve

Could synthesize enzymes capable of breaking downother organic compounds

Could synthesize enzymes capable of building and

maintaining cell membranes

Later DNA could have evolved as method ofconveniently & safely

Storing vital chemical info contained in cell RNA


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The First Cells

Age of microbes3.5 billion years ago

1. The earliest living cellsanaerobic

prokaryotes

2. Photosynthetic bacteria and the

evolution of an oxygen-rich environment

3. Development of aerobic metabolism


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II. The first cells

The rise of eukaryotesabout

1.4 billion years ago

1. Endosymbiotic hypothesis

2. The origin of the nucleus

1. Anaerobic, predatory

prokaryotic cell engulfs


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prokaryotic cell engulfs

an aerobic bacterium.

2. Descendants of engulfed

bacterium evolve into

mitochondria.

3. Mitochondria-containing

cell engulfs a photosynthetic

bacterium.

4. Descendants of photosynthetic

bacterium evolve into chloroplasts.

aerobic

bacterium


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First Cell Types

Heterotrophic cells

Incapable of producing their own food

Autotrophs Can produce chemicals to store energy

Chemoautotrophs

Store energy found in certain inorganic chemicals


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First Cell Types

Most organisms found free oxygen intolerable

In oceans

Organisms that built simple and complex organic

compounds

Removed CO2 from the atmosphere

More advanced autotrophs removed most of the rest

& replaced it with oxygen

The excess oxygen changed forever chemical natureof atmosphere to todays


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Further Evolution of First Cells

First cells, prokaryotes, were always simple

in structure

2 - 1.5 billion years ago A new cell appearedeukaryotes

Had membranes to isolate certain chemical

reactions

Cellular life then evolved into what we know

today


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Archaea & Bacteria Domains

Directly related to oldest organisms on

earth

Have had lots of time to evolve & differentiate

Thrive nearly everywhere

Depths of oceans & Earth, all surfaces

M lti ll l i


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Multicellular organisms

A. Advantages of multicellularity

B. Challenges of multicellularity

C. The first multicellular organisms

1. Plantsprimitive marine algae

2. Animalsmarine invertebrates

D. The transition to land

1. Advantages of terrestrial living

2. Challenges of terrestrial living

III M lti ll l i


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III. Multicellular organisms

The transition to land

The evolution of land plants

a. The first land plants

1) Mosses and ferns 2) Continued water dependency

b. Conifersthe invasion of dry habitats

c. Flowering plants

1) The dominant plant form today

2) Pollination by insects

III M lti ll l i


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D. The transition to land

The evolution of terrestrial animals a. Arthropods

b. Lobefin fish to amphibians

c. Amphibians to reptiles 1) The age of the dinosaurs

2) Reptiles and maintenance of body temperature

d. Birds 1) Insulating feathers retain body heat

2) Evolution of feathers for flight

III M lti ll l i


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The evolution of terrestrial animals

e. Mammals

1) Insulating hair retains body heat

2) Live births and mammary glands

IV H man e ol tion


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IV. Human evolution

A. Primate evolution

1. Grasping handsprecision grip and

power grip

2. Binocular and color vision with

overlapping fields of view

3. Large brainallows fairly complex social

systems

H.habil is


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Ardip i thecusramidus

Austra lop i thecusafarensis

H. heidel-bergensis

A. boisei

A. afr icanus

A. robustus

H.sapiens

H. erectu s

Homo ergaster

H. neanderth alensis

IV Human evolution


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IV. Human evolution

Hominid evolution

1. The evolution of dryopithecinesbetween

20 and 30 million years ago

2. Australopithecinesthe first true hominids

a. Appeared 4 million years ago as evidenced by

fossils

b. Walked upright

c. Large brains

IV Human evolution


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IV. Human evolution

3. Homo habilis2 million years ago

a. Larger body and brain

b. Ability to make crude stone and bone tools

4. Homo erectus1.8 million years ago

a. Face of modern human

b. More socially advanced c. Sophisticated stone tools aided in hunting

d. Used fire

IV Human evolution


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IV. Human evolution

5. Homo sapiens200,000 years ago

a. Neanderthals evolved 100,000 years ago

1) Similar to humansmuscular, fully erect,

dexterous, large brains

2) Developed ritualistic burial ceremonies

b. Cro-Magnons evolved 90,000 years ago

1) Direct descendants of modern humans

2) Were artistic and made precision tools

lec15+origin of life

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