Beginnings
Evolution
Biology 4974/5974
D.F. Tomback
Biology 4974/5974
Evolution
Beginnings
Figures from: Hall and Hallgrimsson (2008, 2014) Strickberger’s
Evolution, 4th & 5th ed., Jones and Bartlett
From simple molecules….life evolved. Complexity has
resulted entirely from self-organization, based on first
principles of chemistry with natural selection the driving
force.
Learning goals: Know and understand
• The early formation of the universe, our solar system, and earth; the relative
importance of dark matter, dark energy, and normal matter.
• The composition of the first atmopshere, and the next more stable
atmosphere and its chemical properties.
• Proposals about where the origin of the organic building blocks (chemicals)
of living organisms could occur.
• The experimental and empirical evidence for abiotic synthesis of organic
molecules.
• Which groups of organic molecules have been synthesized abiotically.
Origin of the Universe and Formation of
the Earth and Atmosphere
The universe formed about 13.7 billion years ago
(bya). Evidence:
• Cosmic microwave background (microwave photons)
fills observable universe.
• Shows fluctuations, reflecting early structure.
Confirmed by:
• Cosmic Background Explorer (COBE—1992).
• Wilkinson Microwave Anisotropy Probe (WMAP—
2001).
Evidence supports the Big Bang theory (aka the
Evolutionary Universe)
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Beginnings
Evolution
Space-time inflation, expansion,
confirmed by red-shift. The greater the
age of the object, the greater the shift.
Biology 4974/5974
D.F. Tomback
Fig. 4.1
Fig. 4.1
Current view of the universe
The universe is flat and mostly composed of
dark energy and very little ‘ordinary’ matter
Fig. 4.2
The solar system formed
about 4.6 billion years ago
Condensation theory or nebular
hypothesis (Kant 1755):
• The sun and planets condensed from
a cloud of dust and gas.
• Center mass—gravitational force
produced pressure and heat, causing
thermonuclear reactions—the sun.
• Sun surrounded by accretion disk.
• Dust particles adhered; bodies > 1 km,
grew by gravity.
• Inner rocky planets, outer gaseous
planets, because of solar wind .
Fig. 4.3
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Beginnings
Evolution
Biology 4974/5974
D.F. Tomback
Atmospheres
First atmosphere:
• Hydrogen and helium.
• Core heat, weak gravity, solar wind caused loss
of light gases.
Second atmosphere:
• More stable second atmosphere: 4.2 to 3.8 bya.
• Composition: mostly H2O, CO2
• Smaller amounts: N2 , H2 ,CH4 , CO , NH3 , HCl
H2S.
What critical gas is missing?!
• Greenhouse gases, causing warming.
Third atmosphere: to be discussed later!
The earth cooled and water vapor
condensed, producing torrential rains
Oceans formed in lower part of earth’s crust:
• Contained dissolved CO2 resulting in
carbonates.
• Contained dissolved salts and minerals.
• Included dissolved methane and ammonia.
• High salinity was achieved early in the
formation of earth.
Earth is unique
• Medium-sized sun.
• Orbit good distance from sun and
regular shape: heat and light and stable
climate.
• Mix of elements supports life.
• Maintains liquid water, a stable solvent.
• Iron core produces a magnetic field that
deflects most solar and cosmic
radiation.
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Beginnings
Evolution
Biology 4974/5974
D.F. Tomback
Abiotic synthesis of organic molecules
Different possibilities for where life originated:“
• Exogenous delivery” or “Panspermia” (via meteors)
• Hydrothermal vent systems
• On clay substrates
• Oceans and ponds “organic soup”
What is life? (Box 6-2) (Wilson 2005) :
• Have parts that are heterogeneous and specialized
• Include a variety of internal mechanisms
• Contain diverse organic molecules, including nucleic acids and
proteins
• Grow and develop
• Reproduce
• Repair themselves when damaged
• Have metabolism
• Undergo environmental adaptation
• Construct the niches that they occupy
The first life on earth was probably simple in
structure and function, meeting the basic
requirements for survival and replication
• Aleksandr I. Oparin, a Russian biochemist,
author of The Origin of Life on Earth in 1924.
• J. B. S. Haldane, a British biochemist and
geneticist.
Each independently contributed an outline of
events for the origin of life on earth in the
“organic soup.”
Conditions after the earth was formed
favoring abiotic synthesis of organics
• Reducing atmosphere--presence of H2 and Hcontaining compounds.
• Circular orbit around sun, no temperature
extremes.
• Large quantity of stable solvent--water.
• Presence of critical elements (H,O, C, N, S, P,
and Ca).
• Abundance of energy sources: lightning, solar
radiation (including UV), cosmic radiation (no
ozone layer).
• No microorganisms as consumers.
• Plenty of time—billions of years—so chance
events possible.
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Beginnings
Evolution
Biology 4974/5974
D.F. Tomback
First laboratory demonstration of abiotic synthesis of
organic molecules by Stanley Miller (1953)
• Recreated early conditions.
• Started with ammonia, methane, hydrogen, water.
• Electrical discharge ran 24 hrs per day, 7 days.
Trap for
sampling
Comparing results from Miller’s experiments
and the Murchison meteorite (1969):
Many complex organic molecules have been synthesized
abiotically from simple organic precursors under reducing
conditions:
Simple pathways have been suggested for the early
synthesis of five groups of organic molecules:
• Aldehydes
• Sugars
• Purines and pyrimidines
• Fatty acids
• Pyrroles and porphyrin rings
For example, pyrrole units and formaldehyde may
combine to make porphyrin rings.
• These combine with a metal ion, such as iron or
magnesium.
• Forms the backbone for chlorophyll, hemoglobin,
cytochrome c, and other respiratory enzymes.
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Beginnings
Evolution
Biology 4974/5974
D.F. Tomback
Simple organic molecules could accumulate through
time, without being oxidized or consumed—WHY???.
The next step: production of complex molecules by
polymerization reactions.
• Polymerization requires energy input----dehydration
reaction: removal of water to form a bond between
monomers.
Sidney Fox in the 1960’s proposed that polymerization of
simple organics could occur spontaneously on the shores
of lakes and oceans.
• He showed that organics can adsorb to a clay layer.
The thin water layer evaporates, and a bond forms.
• He proposed that tidal action deposits organics on shore
and pulls polymers back into the water.
Hydrothermal vents and volcanic areas could
provide conditions for organic synthesis
• More than 100 vents known.
• Have reducing chemical environments, similar
to early atmosphere.
• Produce ammonia and amino acids abiotically
today.
• Metallic catalysts, such as iron pyrite, may
have been used in early synthesis.
• Ammonia found to be stable under heat, and
alanine synthesized under these conditions.
• Some ancient prokaryotes were thermophiles.
• Scientists finding heat-tolerant organisms live
at vents.
Study guide
1. What event initiated the formation of our universe? What
is the composition of the universe? How did our solar
system form?
2. What was the first atmosphere composed of and its fate?
What was the composition of the second atmosphere?
What kind of chemical environment does it represent?
3. What are possible places/conditions where organic
molecules were first synthesized abiotically?
4. What kinds of evidence demonstrate that abiotic
synthesis of organic molecules is possible?
5. What groups of organics have been synthesized
abiotically? What about macromolecules—how could
they be synthesized abiotically?
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