The Origin of Life, Ch 26, U301PP

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The Origin of Life, Ch 26, U301PP
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• Changing Life on a Changing Earth
• Life is a continuum
• Extending from the earliest organisms to the
  great variety of species that exist today

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A brief history of time
4.6 BYA
20 BYA
3.8 BYA
Origin of Life?
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Models for lifes origins

• Spontaneous origin of life on earth
• Warm little pond- Darwin
• rich brew of organic chemicals interacted, formed
  first living beings
• Hot earth Stetter
• hydothermal vents, harsh conditions (hot water,
  sulfur) may have produced some early beings
• Deep sea model Fox
• isolation in the oceans may have protected early
  formation of living beings
• Extraterrstrial origin (Panspermia) Hoyle early
  Earth was too hostile living things came from
  outer space and seeded Earth
• Supernatural (creation by a deity)- Could life
  have arisen from a supernatural being, deity, or
  force?
• We cannot rule out religious or faith-based ideas
  because they are untestable scientifically (nor
  can we rule them in for the same reason)

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What IS Life?

• Life does have emergent, fundamental properties
• cellular organization growth
• development
  reproduction
• regulation and homeostasis metabolism
• respond to stimuli heredity (able
  to pass on traits)

However
lets use this definition for now An entity
that can reproduce imperfectly (reproduction and
adaptation)
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• Concept 26.1 Conditions on early Earth made the
  origin of life possible
• Most biologists now think that it is at least a
  credible hypothesis
• That chemical and physical processes on early
  Earth produced very simple cells through a
  sequence of stages

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Early Earth

• Atmosphere thick with water vapor- after the
  earth cooled, seas began to form
• High temperatures- oceans thought to be 49-88C
  (120-190F)
• UV radiation strong (no ozone layer)
• Volcanic eruptions spewed gases into atmosphere
  (CO, CO2, N2,)
• Heavy meteorite bombardment
• Atmosphere consisted of carbon dioxide, nitrogen,
  hydrogen sulfide (H2S), ammonia (NH3), methane,
  (CH4). May have been rich in H2. Very little to
  no atmospheric oxygen was present
• Reducing atmosphere (favors electron additions,
  bondings). Atmosphere is oxidizing today

Life started HERE?
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For life to have originated on earth, you need
the following 1. synthesis of organic compounds
Darwins warm little pond. ah.
Where could the organic materials have come from?
Oparin and Haldane suggested the atmosphere had
been reducing and could form organic molecules
(1920s)
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• Laboratory experiments simulating an early Earth
  atmosphere
• Have produced organic molecules from inorganic
  precursors (yielded glycine, alanine (amino
  acids), hydrogen cyanide, acetic acid, formic
  acid, urea, adenine (one of the bases of DNA and
  RNA)
• Similar experiments have identified more than 30
  different carbon compounds
• but the existence of such an atmosphere on early
  Earth is questioned as unlikely

EXPERIMENT
Miller and Urey set up a closed system in their
laboratory to simulate conditions thought to
have existed on early Earth. A warmed flask of
water simulated the primeval sea. The strongly
reducing atmosphere in the system consisted of
H2, methane (CH4), ammonia (NH3), and water
vapor. Sparks were discharged in the synthetic
atmosphere to mimic lightning. A condenser
cooled the atmosphere, raining water and any
dissolved compounds into the miniature sea.
Electrode
CH4
Water vapor
H2
NH3
Condenser
Cold water
RESULTS
As material circulated through the apparatus,
Miller and Urey periodically collected samples
for analysis. They identified a variety of
organic molecules, including amino acids such as
alanine and glutamic acid that are common in the
proteins of organisms. They also found many
other amino acids and complex,oily hydrocarbons.
Cooled water containing organic molecules
CONCLUSION
H2O
Organic molecules, a first step in the origin
of life, can form in a strongly reducing
atmosphere.
Sample for chemical analysis
Figure 26.2
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A hot earth the source of organic molecules?

• Hot sulfur, anaerobic conditions?

Karl Damn Hot Stetter
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How about deep sea vents?

• Instead of forming in the atmosphere
• The first organic compounds on Earth may have
  been synthesized near submerged volcanoes and
  deep-sea vents

Figure 26.3
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Or maybe an Extraterrestrial Sources of Organic
Compounds

• Some of the organic compounds from which the
  first life on Earth arose
• May have come from space
• Carbon compounds
• Have been found in some of the meteorites that
  have landed on Earth

Panspermia suggests that LIFE came from outer
space, but at the very least some elements of
life may have arisen elsewhere
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Looking Outside Earth for Clues About the Origin
of Life

• The possibility that life is not restricted to
  Earth
• Is becoming more accessible to scientific testing

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2. Abiotic Synthesis of Polymers

• Small organic molecules
• Polymerize when they are concentrated on hot
  sand, clay, or rock

October 2003- A team at the Howard Hughes Medical
Institute and Massachusetts General Hospital in
Boston said they had shown materials in clay were
key to some of the initial processes in forming
life. Specifically, a clay mixture called
montmorillonite not only helps form little bags
of fat and liquid but helps cells use genetic
material called RNA. That, in turn, is one of the
key processes of life. Jack Szostak, Martin
Hanczyc and Shelly Fujikawa were building on
earlier work that found clays could catalyze the
chemical reactions needed to make RNA from
building blocks called nucleotides. They found
the clay sped along the process by which fatty
acids formed little bag-like structures called
vesicles. The clay also carried RNA into those
vesicles. A cell is, in essence, a complex bag of
liquidy compounds. "Thus, we have demonstrated
that not only can clay and other mineral surfaces
accelerate vesicle assembly, but assuming that
the clay ends up inside at least some of the
time, this provides a pathway by which RNA could
get into vesicles," Szostak said in a statement
Thursday. "The formation, growth and division of
the earliest cells may have occurred in response
to similar interactions with mineral particles
and inputs of material and energy," the
researchers wrote in their report, published in
the journal Science. "We are not claiming that
this is how life started," Szostak stressed.
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3. Formation of protobionts

• Protobionts
• Are aggregates of abiotically produced molecules
  surrounded by a membrane or membrane-like
  structure

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• Laboratory experiments demonstrate that
  protobionts
• Could have formed spontaneously from abiotically
  produced organic compounds
• For example, small membrane-bounded droplets
  called liposomes
• Can form when lipids or other organic molecules
  are added to water

?
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Figure 26.4a, b
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4. The beginning of inheritanceThe RNA World
and the Dawn of Natural Selection

• The first genetic material
• Was probably RNA, not DNA
• relatively simple,
• can replicate by complementary base pairing
  techniques (5-10 base pairs long, up to 40 if
  zinc is present (1 error rate)
• important catalysts in modern cells ribozymes
  are RNA catalysts (can help make new RNA, rRNA,
  mRNA, tRNA) and serve as its own enzyme
• can assemble spontaneously into small polymers
  and longer polymers in the presence of clay

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• RNA molecules called ribozymes have been found to
  catalyze many different reactions, including
• Self-splicing
• Making complementary copies of short stretches of
  their own sequence or other short pieces of RNA

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• Early protobionts with self-replicating,
  catalytic RNA
• Would have been more effective at using resources
  and would have increased in number through
  natural selection

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Panspermia

• This electron microscope image is a close-up of
  the center part of photo number S96-12301 (a
  meteorite that was found in Antarctica). While
  the exact nature of these tube-like structures is
  not known, one interpretation is that they may be
  microscopic fossils of primitive, bacteria-like
  organisms that may have lived on Mars more than
  3.6 billion years ago. A two-year investigation
  by a NASA research team found organic molecules,
  mineral features characteristic of biological
  activity and possible microscopic fossils such as
  these inside of an ancient Martian rock that fell
  to Earth as a meteorite. The largest possible
  fossils are less than 1/100th the diameter of a
  human hair in size while most are ten times
  smaller. NASA caption and photo.
• One Australian meteorite contained more than 80
  amino acids (more than we have on earth today!)

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• Concept 26.2 The fossil record chronicles life
  on Earth
• Careful study of fossils
• Opens a window into the lives of organisms that
  existed long ago and provides information about
  the evolution of life over billions of years

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How Rocks and Fossils Are Dated

• Sedimentary strata
• Reveal the relative ages of fossils

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• Index fossils
• Are similar fossils found in the same strata in
  different locations
• Allow strata at one location to be correlated
  with strata at another location

Figure 26.6
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• Relative dating
• Absolute dating of fossils
• Can be determined by radiometric dating

Figure 26.7
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Radiometric dating of fossils

• As soon as a living organism dies, it stops
  taking in new carbon. The ratio of carbon-12 to
  carbon-14 at the moment of death is the same as
  every other living thing, but the carbon-14
  decays and is not replaced. The carbon-14 decays
  with its half-life of 5,700 years, while the
  amount of carbon-12 remains constant in the
  sample. By looking at the ratio of carbon-12 to
  carbon-14 in the sample and comparing it to the
  ratio in a living organism, it is possible to
  determine the age of a formerly living thing
  fairly precisely. A formula to calculate how old
  a sample is by carbon-14 dating is
• t ln (Nf/No) / (-0.693) x t1/2
• where ln is the natural logarithm, Nf/No is the
  percent of carbon-14 in the sample compared to
  the amount in living tissue, and t1/2 is the
  half-life of carbon-14 (5,700 years).
• So, if you had a fossil that had 10 percent
  carbon-14 compared to a living sample, then that
  fossil would be
• t ln (0.10) / (-0.693) x 5,700 years t
  (-2.303) / (-0.693) x 5,700 years
• t 3.323 x 5,700 years
• t 18,940 years old
• More simply, calculate how many half lives have
  elapsed, and multiply x 5700, e.g., a sample
  with 3 carbon-14, would have gone through 4
  half-lives 22,800 years
• Because the half-life of carbon-14 is 5,700
  years, it is only reliable for dating objects up
  to about 60,000 years old. However, the principle
  of carbon-14 dating applies to other isotopes as
  well. Potassium-40 is another radioactive element
  naturally found in your body and has a half-life
  of 1.3 billion years. Other useful radioisotopes
  for radioactive dating include Uranium -235
  (half-life 704 million years), Uranium -238
  (half-life 4.5 billion years), Thorium-232
  (half-life 14 billion years) and Rubidium-87
  (half-life 49 billion years).

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• The magnetism of rocks
• Can also provide dating information
• Magnetic reversals of the north and south
  magnetic poles
• Have occurred repeatedly in the past
• Leave their record on rocks throughout the world

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The Geologic Record

• By studying rocks and fossils at many different
  sites
• Geologists have established a geologic record of
  Earths history

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• The geologic record is divided into
• Three eons the Archaean, the Proterozoic, and
  the Phanerozoic
• Many eras and periods
• Many of these time periods
• Mark major changes in the composition of fossil
  species

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• The geologic record

Table 26.1
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Mass Extinctions

• The fossil record chronicles a number of
  occasions
• When global environmental changes were so rapid
  and disruptive that a majority of species were
  swept away

Millions of years ago
600
400
300
200
500
100
0
2,500
100
Number of taxonomic families
80
2,000
Permian mass extinction
Extinction rate
60
1,500
Extinction rate ( )
Number of families ( )
40
1,000
Cretaceous mass extinction
20
500
0
0
Carboniferous
Neogene
Cretaceous
Ordovician
Paleogene
Cambrian
Devonian
Permian
Jurassic
Proterozoic eon
Silurian
Triassic
Ceno- zoic
Figure 26.8
Paleozoic
Mesozoic
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• Two major mass extinctions, the Permian and the
  Cretaceous
• Have received the most attention
• The Permian extinction
• Claimed about 96 of marine animal species and 8
  out of 27 orders of insects
• Is thought to have been caused by enormous
  volcanic eruptions

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• The Cretaceous extinction
• Doomed many marine and terrestrial organisms,
  most notably the dinosaurs
• Is thought to have been caused by the impact of a
  large meteor

Figure 26.9
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• Much remains to be learned about the causes of
  mass extinctions
• But it is clear that they provided life with
  unparalleled opportunities for adaptive
  radiations into newly vacated ecological niches

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• The analogy of a clock
• Can be used to place major events in the Earths
  history in the context of the geological record