Download Life in the Universe

Chemical & non-chemical life
FYOS 1001
Lecture 2
Various Alien Life Forms
Because of our limited perception, we may be quite biased as
… a person in a small local Chinese village may convince that only the
Chinese language exists in the world (since it is the only one spoken
by all the people around!)…
Life can take place in a wide variety of environments very different from Earth
their life forms can be quite different from us, in harmony with their local
conditions.
a life can arise from repeated interactions among its constituent subunits…
Barnard 68 : Dark Cloud
Non-chemical Life?
• “Black cloud”
In the science fiction written by a British
astronomer, Fred Hoyle…
Giant interstellar cloud
 Can think and move
 Networks of molecules  brain
 Indefinite lifetime
 Thoughts  radio message from one part to
another
 Starlight = energy source
approached to Earth to replenish its
energy…discovered human and make a
communication!
? Very low density and very low temperature 
very slow chemical reaction  really long time
for evolution…
• Entire galaxy as a living organism
Non-chemical Life?
• Life based on gravitational force
• Stars are the subunit as atoms in our body
• Stars interact on a time scale of many
millions of years.
• If we think that a life can be arisen from
repeated interactions among stars…
 millions of such interactions are needed for
life to begin at the molecular level.
 Universe is far too young to have such life
forms!
Life on Neutron Stars
Non-chemical Life?
Frank Drake… • Strong force based life…
• Surface temperature ~ 1million degrees,
enormous gravity…  no molecules (not
even atom) can survive.
• Nuclei would last for only 10-15 second,
however this can be equivalent to a lifetime!
evolution (or change in life) happens faster
Entire civilizations could rise and fall a
million times while a human eye can wink.
If true, no meaningful way to communicate
with them.
•Human (170cm) with a speed of about 1m/sec with 70 years of lifetime  1 billion
times of its body size…
•Nuclei of size 10-13 cm with speed of 1000 km/sec and lifetime of 10-15 second 
travel distance = 10-15 sec*1000 km/sec = 10-12 km = 1 million times of its body size!
Let’s Focus on life forms that we can perceive
and possibly communicate
 Chemical Life Forms
Predestinists
• Key chemicals in our Earth biochemistry are
inevitable results of random chemical
synthesis throughout the Universe!
organic syntheses in the Universe have a
direction that favors the production of amino
acids (i.e., building blocks of proteins and
nucleic acids).
(with cosmic abundance of light elements,)
this suggests that life everywhere will be
based not only on carbon chemistry, but the
one similar to our own!
Carbaquists
• Carb (Carbon) + Aqua
(Water):
 C and H2O are inevitable
for life not only on Earth
but everywhere in the
Universe!
Life elsewhere in the Universe must resemble
that present on Earth, because no other basis
for life can exist!
…
Life everywhere must be based primarily upon
C, H, N, & O and it can arise only in water
…
Learn your biochemistry here on Earth, then
you will understand the Life of the Universe!
There are 103 elements known to exist.
Why not a life form with an iron skeleton and using methanol?
Earth Life is Carbon-Based
• Life on Earth is made from more
than 20 chemical elements, but
four elements make up about 96%
of the mass.
(right figure) chemical composition
of the human body by weight.
Oxygen  mostly in H2O
Cell structures and their functions
are due to Carbon  Carbonbased life!
Any chemical compounds contain C
 “organic compound”
Relative abundance of chemical elements in the Universe
• Cosmic Abundance
How?
via Nuclearsynthesis
Examples of Good pairs are
H + F  Hydrogen Floride
Na + Cl  Sodium Chloride (salt)
or 2H + O  H2O
Chemical bonding
• Elements want to have electrons in certain numbers!
2, 10, 18, etc.
• Thus an element with 11 electrons wants to get rid of one electron while an
element with 7 electrons wants to accept one more electron from
somewhere
 Chemical reactions
covalent bond : sharing an electron (s)
Ionic bond : Example of a chemical
bonding that makes up salt
Why Carbon-based?
Any other base
element?
• C60 (Bucky-balls)
Entirely made of Carbon.
(superconductor material, etc.)
Requirements for the base element:
o Abundant element
o Combine easily with itself and others
• Advantages of Carbon!
Let’s consider all different ways of combining with
Hydrogen…
1. Oxygen : H2O and H2O2
2. Nitrogen : NH3 (ammonia) and N2H2
(hydrazine)
3. Carbon : so many different ways…
E.g., C90H84 or C167H336, …
# of possible isomers for C167H336 = 9×1083
? Can this may be due to the difference in the
maximum number of bondings for C (No=4),
O (No=2), N (No=3)?
• Then why not Si-based life?
Silicon-based Life?
• Si has four “bonds”
similar to Carbon.
For example, CH4 (methane), SiH4 (silane).
o Si-Si bond strength is ½ of the C-C bond
o C-C, C-H, and C-O bond strengths are ~same,
but Si-H and S-O bonds are stronger than Si-Si
 hard to make a large complex structures
(chain, rings, etc.)
o At low temperature, nearly all Si atoms will
form SiO2 (quartz!) and this rock-forming
material are very difficult to dissociate!
Although life based on silicon may be possible,
it will be extremely uncommon at best!
Life based on carbon seems favored as the
dominant kind of life in the Universe!
Carbaquists…
no alternative?
Convincing argument…
But there are other alternatives for solvent!
• Carbon + water may be the most efficient
basis of life in the Universe, but not the only!
• Cannot be convinced (or
refuted) purely based on
reasoning and analogy.
A discovery of noncarbon based alien life
form quickly solves the
issue.
Or a series of
discoveries of alien life
forms that are all
carbon+water…
• Less efficient bases can be used…
Information Storage as an example:
o In English :
26 capital, 26 small letters, plus few
punctuation marks (~60 “symbols”)
o In computer:
01001001 01101110 00100000 01000101 01101110 01100111 01101100 01101001
01110011 01101000 00100000 00111010 00100000 00110010 00110110 00100000
01100011 01100001 01110000 01101001 01110100 01100001 01101100 00101100
00100000 00110010 00110110 00100000 01110011 01101101 01100001 01101100
01101100 00100000 01101100 01100101 01110100 01110100 01100101 01110010
01110011 00101100 00100000 01110000 01101100 01110101 01110011 00100000
01100110 01100101 01110111 00100000 01110000 01110101 01101110 01100011
01110100 01110101 01100001 01110100 01101001 01101111 01101110 00100000
01101101 01100001 01110010 01101011 01110011 00100000 00101000 01111110
00110110 00110000 00100000 10010011 01110011 01111001 01101101 01100010
01101111 01101100 01110011 10010100 00101001
o In Korean :
26 모음, 26 자음, 몇가지 부호 (약60개 심볼)
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• Next Week’s presentations
o Nuclearsynthesis (Big Bang, Stellar, and Supernova)
o Habitability of Planets
o Unique characteristics of Water