Transcript Quantum Well Electron Gain Structures and Infrared

Origins of Life
Stephen Eikenberry
18 January 2013
AST 2037
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POP QUIZ!!
1. The Earth's atmosphere is mostly made of what
element?
2. What element is the most versatile in its bonding (and
critical for life)?
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How Did Life Come About?
• First things first: I don’t know!
• Second: Anyone who says they have a proven scientific
explanation (currently) is probably selling something!
• That said … there ARE some things we know, and some we
strongly suspect
• From them, we can at least TRY to put together a rough sketch
of how life probably arose here on Earth
• Let’s do that!
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What do we have to work with?
• In the beginning …
• OK, well, not really the beginning. More like:
• About 8 billion years after the Big Bang
• About 500 million years after the Solar System began to
form
• About 4.6 billion years before TODAY
• What was Earth like?
• Young, recently-solidified surface
• Accretion of material from planetesimals nearing an end
(end of the “Early Heavy Bombardment”)
• How do we know?
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Earth: T – 4.6 Billion Yrs
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Rocks were just solidifying on surface
How do we know? Age-dating of the oldest known rocks
From what? Radioactive isotope dating
Huh?
First: what’s an isotope?
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Elements and Isotopes
• An “element” has a certain number of protons and electrons
• For instance, hydrogen (H) has 1 of each
• Oxygen (O) has 8 of each
• Carbon (C) has 6 of each
• “Isotopes” of a given element have the same number of
protons/electrons, but different numbers of neutrons in the
nucleus:
• “Normal” H has 0 neutrons, deuterium has 1 neutron,
tritium has 2 neutrons – but ALL are still hydrogen
• O16 is “normal” oxygen, most common – has 8 protons
and 8 neutrons (8+8 = 16)
• O18 is more rare (8 protons + 10 neutrons = 18)
• C12 (6+6) is common, C14 (6+8) is rare – and radioactive!!
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Radioactive Decay
• Many non- “normal” isotopes are radioactive, and
they “decay” into other elements
• This process converts a “parent” to a “daughter”
isotope
• This happens on a known timescale called the
“half-life” of the decay (the time it takes for ½ of
the parent atoms to decay)
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Radioactive Age-Dating
• So … by counting
parent/daughter atoms
inside a rock, we KNOW
how many half-lives since
the rock solidified from
magma
• We can measure the
atomic half-life in a
physics lab (or, even
calculate it from quantum
physics these days)
• Then, we know HOW
OLD the rock is …
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Some Handy Decays
Parent Isotope
Stable Daughter
Product
Half-Life
Uranium-238
Lead-206
4.5 billion yr
Uranium-235
Lead-207
704 million yr
Thorium-232
Lead-208
14.0 billion yr
Rubidium-87
Strontium-87
48.8 billion yr
Potassium-40
Argon-40
1.25 billion yr
Samarium-147
Nedodymium-143 106 billion yr
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Earth: T – 4.4 Billion Yrs
• Atmosphere & oceans – non-existent!!
• How do we know? Rocks formed back then had very little
“volatiles” in them (i.e. H, H2O, O2, etc.)
• What happened to volatiles? Solar wind (show)
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How Did We Get Oceans?
• From Outer Space! Comet/Ocean Theory:
• Comets (big balls of ice) crash into baby Earth
• Crash melts/vaporizes the ice
• Once the steam cools, it condenses
• The liquid water flows “downhill” and pools together
• This makes oceans
• Also brings lots of other “volatile” materials
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Cometary Bombardment
• We KNOW comets hit planets
– Jupiter & Comet
Shoemaker-Levy 9
• Consistent with Early Heavy
Bombardment (how do we
know? Moon craters)
• Deuterium problem: Most
current comets we see have
water with too little
deuterium compared to water
in Earth’s oceans
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Deuterium Issue Resolved!
• We know from meteors & space probes that the inner Solar
System has more heavy isotopes than the outer Solar System
• We think this is due to the solar wind
• Almost all known comets today are in the outer SS
• But, back in the day, inner SS would have had comets too
(those are the most likely to hit Earth in the Early Heavy
BB!)
• Suggestion: Maybe inner SS comet water would have
deuterium abundance like Earth’s ocean water (?)
• In 2005, Gemini Observatory measured deuterium
abundance from H20 in asteroid belt comets  matches
Earth water !!!
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What was our Young Atmosphere
Like?
• Unbreathable!
• Mostly carbon monoxide (CO), carbon dioxide (CO2),
nitrogen (N2) and water vapor (H2O)
• How do we know? Rock chemistry from that time period
shows these compounds
• But … no O2
• Note: free oxygen is very “aggressive” in forming chemical
bonds and does bad things to many chemicals (i.e. iron
rusts!)
• So … even a little O2 would be pretty obvious in these rocks
 it just wasn’t there!
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Summary So Far
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Then … Life Appears!
• First fossil cells found in rocks
at about T – 3.7 to T – 3.5 Billion
Years!
• Tiny little things
• Not O2 breathers like us (none
around!)
• Probably CO2 breathers
• Modern cyanobacteria look a lot
like these fossils AND they are
CO2 breathers
• Suggests that the first (fossil) life
may have been cyanobacteria (?)
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HOW Did Life Appear?
• It must have formed SOMEHOW!
• What do we need?
• Atmosphere – got one!
• DNA or something like it – not obviously there (!)
• COULD DNA form back then?
• Need amino acids, sugars, phosphates  DNA
building blocks
• Could THEY form?
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Urey-Miller Experiment
• Basic idea:
• Take a bunch of chemicals as
known to present in the early
atmosphere & ocean
• Put them in a chemistry lab
setup with circulating gases
• Simulates “Primordial Soup”
• Zap the whole thing with
electric discharge (like
lightning!)
• See what happens …
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Urey-Miller: Results
• What did they find?
• Amino Acids!!!
(Lots of them!)
• More specifically:
• 13 amino acids used in life; (both L- and R- type)
• Sugars
• Lipids
• About 10-15% of the carbon ended up in protein
structures like this
• Summary: With the KNOWN chemicals
and KNOWN environment in the early
Earth, we EXPECT complex amino acids,
sugars, and other organic chemicals to
form in nature (!!)
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Meteor Aminos
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The Murchison Meteorite is a big chunk of space rock
Chemical analysis shows: Amino Acids!
It is another source of aminos!
Diversity?
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List of Murchison Amino Acids
Amino Alkanoic Acids
2 Carbon:
Glycine
3 Carbon:
Alanine
b-alanine
Serine
Sarcosine
4 Carbon:
Threonine
a-Aminobutyric Acid
b-Aminobutyric Acid
g-Aminobutyric Acid
a-Aminoisobutyric Acid
b-Aminoisobutyric Acid
N-Ethylglycine
N,N-dimethylglycine
N-Methylalanine
N-methyl-b-alanine
5 Carbon:
Valine
Isovaline
Norvaline
Proline
Methionine
3-Amino-2-ethylpropanoic Acid
3-Amino-2,2-dimethylpropanoic Acid
3-Amino-2-methylbutanoic Acid
3-Amino-3-methylbutanoic Acid
4-Amino-2-methylbutanoic Acid
4-Amino-3-methylbutanoic Acid
Allo-3-amino-2-methylbutanoic Acid
3-Aminopentanoic Acid
4-Aminopentanoic Acid
5-Aminopentanoic Acid
Amino Dialkanoic Acids
4 Carbon:
Aspartic Acid
5 Carbon:
Glutamic Acid
2-Methylaspartic Acid
3-Methylaspartic Acid
Allo-3-methylaspartic Acid
N-Methylaspartic Acid
6 Carbon:
a-Aminoadipic Acid
2-Methylglutamic Acid
7 Carbon:
a-Aminopimelic Acid
Amino Alkanoic Acids
6 Carbon:
Leucine
Isoleucine
Alloisoleucine
Norleucine
Pseudoleucine
Cycloleucine
2-Methyl-norvaline
Pipecolic Acid
2-Amino-2-ethylbutanoic Acid
3-Amino-2-ethylbutanoic Acid*
2-Amino-2,3-dimethylbutanoic Acid
3-Amino-2,3-dimethylbutanoic Acid*
4-Amino-3,3-dimethylbutanoic Acid*
3-Amino-3-methylpentanoic Acid*
4-Amino-2-methylpentanoic Acid*
4-Amino-3-methylpentanoic Acid*
4-Amino-4-methylpentaoic Acid*
3-methylamine-pentanoic Acid*
4-Aminohexanoic Acid*
7 Carbon:
2-Amino-2,3,3-trimethylbutanoic Acid
2-Amino-2-ethyl-3-methylbutanoic Acid
2-Amino-2-ethylpentanoic Acid
2-Amino-3-ethylpentanoic Acid
2-Amino-2,3-dimethylpentanoic Acid
2-Amino-2,4-dimethylpentanoic Acid
2-Amino-3,3-dimethylpentanoic Acid
2-Amino-3,4-dimethylpentanoic Acid
2-Amino-4,4-dimethylpentanoic Acid
Allo-2-amino-2,3-dimethylpentanoic Acid*
Allo-2-amino-3,4-dimethylpentanoic Acid
2-Amino-2-methylhexanoic Acid
2-Amino-3-methylhexanoic Acid
2-Amino-4-methylhexanoic Acid
2-Amino-5-methylhexanoic Acid
Allo-2-amino-3-methylhexanoic Acid*
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Meteors: Source for Life?
• Note: L/R evenly made here too
• Is this the source?
• Probably not:
• Not that much amino abundance, and the
compounds are stuck inside a rock
• To get enough on Earth, need lots of
bombarding
• (but that melts rocks and destroys aminos)
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Got Aminos, etc. – Now What?
• Then, need to put them all together in polymer chains
• “Polymerization” of the Primordial Soup
• How … ??
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Polymerization
• In order to polymerize organic compounds, we would need:
• Stable environment
• No big temperature variations
• No major mechanical shaking
• Lots of surface area
• Points for the various organic compounds to attach
• Perhaps a pattern to it
• Provides chemical/physical energy advantage for pattern
formation in the polymer too
• Where do we find that?
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Clays
• Naturally-occurring silts made
from silicates
• Clay in water can provide
steady temperature and protect
anything inside from
shaking/waves
• Tend to crystalline-like
structures (patterns) with
HUGE surface area
• Known to assist (“catalyze”)
organic reactions in labs
• Could they be the place
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Life’s Little Irony
• Stereotypical Creationist to Stereotypical Evolutionist:
You’re an arrogant fool!
• Stereotypical Evolutionist to Stereotypical Creationist:
You’re an arrogant fool!
• Question to both: How do you make humans?
• Creationist: God scooped up some clay, molded it to human
shape, and breathed on it.
• Evolutionist: Well, see … first you get yourself some nice
clay …
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Direct jump to DNA?
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Maybe … but that is a lot of change of complexity in one hop!
RNA is simpler than DNA
Some critters (i.e. some viruses) seem to run on RNA-only
But … they seem to be dependent on DNA-bearing hosts for
survival (??)
• At least opens the possibility of “RNA world” life, which then
evolved into more complex “DNA-world” we all know and
love today
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Another theory
• Panspermia:
Life is commonly present out in
space, and was carried to Earth as spores trapped in
meteors
• But … radiation issues make this seem a little less
likely
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Summary
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Earth of Way Back When was different
We can tell from chemical and radio-isotope analysis of rocks
Water and other volatiles may have come from comet impacts
Life formed a long time ago – about 3.5 Billion Yr or so
We know from fossils
We don’t know exactly how, but …
• We know we had the right elements
• Those elements + lightning make amino acids
• DNA may have originated from these acids in a clay matrix
• Next question: How did things get from Then to Now??
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