Transcript Silicon Based Life Forms

Silicon Based Life Forms
Life on Earth
Chemistry of life on Earth
-organic
-Carbon based
-water used as solvent
-from water come hydrogen bonds, which give
structural stability to large biomolecules (proteins,
nucleic acids)
-other biologically important atoms hydrogen,
nitrogen, oxygen, phosphorus, and sulfur
Basic Facts about Carbon
Atomic Number = 6
Atomic Symbol = C
Atomic Weight = 12
Melting Point = 3500 C
Boiling Point = 4827 C
6th most abundant element in
the universe
http://www.chemicalelements.com/elements/c.html
Periodic Table
Basic facts about Silicon
Atomic Number = 14
Atomic Symbol = Si
Atomic Weight = 28.21
Melting Point = 1414 C
Boiling Point = 3265 C
http://www.chemicalelements.com/elements/c.html
Silicon in the Solar System
-Present in the Sun and Stars
-Principal component of a class of meteorites known
as aerolites
-group of meteorites chiefly containing silicates
-Makes up 25.7% of Earth’s crust by weight
-Second most abundant element, behind oxygen
-Sand, quartz, flint, granite, clay,
What Silicon is used for
Produce electronic devices
-exp: transistor, integrated
circuits, solar cells,
computer chips…
-microelectronics
Great semiconductor
Used to make concrete and
bricks
Silicon Implants
Principle ingredient of glass
Why Silicon?
Similar chemical properties to Carbon
-Same number of electrons in the outer
shell
-Four bonding sites
-can form complex molecules
-Both can form longs chains or polymers
Most likely element as a alternative to carbon
History
1891 Julius Scheiner
-Astrophysicist at the University of Potsdam
-First to theorize about possibility of life based on silicon
-Thought Mercury, Venus, and Mars must contain life
-Jupiter, Saturn, and Uranus might contain life
1983 James Emerson Reynolds
-pointed out that the heat stability of silicon compounds might allow life to exist at very
high temperatures
1929 John Haldane
-suggested that life might be found deep inside a planet based on partly molten silicate
-silicate = type of rock that consists of silicon and oxygen
-Forms most of any terrestrial planet’s crust
- the oxidation of iron perhaps providing it with energy.
http://www.daviddarling.info/encyclopedia/H/Haldane.html
Example
Horta
-Star Trek
-can move
through rock
as easily as
humans move
through air
-lay eggs
Example
“Aliens”
Example
“Lithovore”
-resemble a crystal robotic
insect
-consume crystalline
vegetation
-live under very dense and
thick atmosphere
-life based on electric energy
generated by an internal
reactor
-lives underground
http://brattahlid.tripod.com/sw3-82web.htm
Example
Artificial Intelligence
Robots
-can process abstract
thoughts and ideas
Are they alive??
Obstacles Facing Silicon Based Life
Silicon is unstable or very reactive in many conformations
-aromatic rings, long chains, multi-ring chains
Large silicon molecules has never occurred in nature
-Largest silicon molecules found only consist of 6 silicon atoms
-will not be able to form large molecules such as proteins
-enzymes are a form of proteins, without enzymes, the chemical
reactions will occur very slowly
Silicon lacks chirality
-left and right handed conformation
-life as we know it utilizes only the right-hand sugars and the left-hand amino
acids
-biochemical reactions for life are very specific
-”for many large biomolecules are so precise that a single conformational
change (right to left) around one carbon atom would block the reaction”
-Bob Hazen (NASA Astrobiology Institute)
-limits the number of different reactions available
Obstacles Facing Silicon Based Life
Silicon combines well with other atoms
-its electronegativity is much less than carbon
-longer bond length
-bonds easier to break
When reacted with oxygen, silicon forms a solid
-carbon dioxide
-silicon dioxide is a solid (sand)
-silicon has a strong affinity for oxygen, so its hard to stop
the oxidation of silicon
-needs a way to get rid of the enormous amount of solid
waste
Much less abundant in the universe than carbon
Requirements for Silicon based Life
1)A method of converting a simple silicon
compound into a more complex and stable
one using an energy source, heat,
electricity, light, sound?
2)The existence of complex silicon compounds
that can serve as energy sources and
catalysts for silicon metabolism
3)Existence of a suitable solvent
Areas Where Silicon Based Life is
Possible
Oxygen Free Environment
Extremely hot environment
Very high pressure
“Earth’s Core”??
-could explain the formation
of deeply buried oil, gas
and mineral deposits
-lived in ancient times ??
http://www.thetech.org/exhibits_events/online/quakes/inside/images/corecore.gif