Silicon Based Life Forms Life on Earth Chemistry

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 6 th 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/sw 3 -82 web. 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/core. gif