https://www.youtube.com/watch?v=g6PDcBhODqo
https://www.youtube.com/watch?v=vjuQRCG_sUw
Life as we don’t know it
The same, even when we’re different
All life on Earth shares:
The same, even when we’re different
All life on Earth shares:
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Carbon basis
Dependence on (liquid) water
DNA/RNA
Reliance on an external energy source
Reasons the structure of life might be fundamental
Element
Percent of human body
Percent of Universe
Oxygen
65
1.0
Carbon
18
0.5
Hydrogen
10
75
Nitrogen
3
0.1
Calcium
1.5
0.007
Phosphorous
1.2
0.0007
Total
98.7
76.6077
The human body is made of many of the most common elements in
the Universe.
Reasons the structure of life might be fundamental
→ Carbon has four valence, or outer, electrons, allowing it to form as
many of four chemical bonds.
Carbon forms more chemical compounds than all other elements
combined.
Reasons the structure of life might be fundamental
→ A solvent is a chemical that dissolves other chemicals. The most
common solvent used by life on Earth is water.
→ Molecules with highly asymmetric electric charge are called polar. Only
polar solvents effectively dissolve other polar compounds.
→ Many building blocks of life, like sugar, are very polar.
Group discussion
How does science fiction reflect our human biases?
In the shadows, under our noses
→ The shadow biosphere is a hypothesis that there may be microscopic
life comprised of different chemistry already on Earth and we just don’t
know it.
We don’t know it exists because:
● Such organisms exist only in extremely remote locations
● Our methods for searching for life today rely on DNA
● Our definition of life is too narrow
Silicon instead of carbon?
→ Silicon has been proposed a replacement for carbon in the complex
chemistry of life.
Pros
●
●
Like carbon, silicon can form four
chemical bonds
Silicon is among the most abundant
elements in the Universe
Cons
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Silicon-based compounds are
comparatively fragile
Bonds with relatively few other
elements
Seven times less abundant than
carbon
Earth life is carbon-based even though there is nearly a thousand
times more silicon than carbon in the crust.
Ammonia instead of water?
→ Ammonia may be able to serve many of the same functions as water
as a biochemical solvent.
Pros
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Abundant in the Universe
Dissolves many organic compounds
and also many metals
Can form both acids and bases
Cons
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More fragile than water
Burns in the presence of oxygen
Ammonia remains liquid at temperatures far cooler than water,
opening up habitability much farther from a star.
Arsenic instead of phosphorous?
→ Arsenic may be able to replace phosphorous in fundamental organic
structures like DNA.
Pros
●
Both share a similar chemical
structure
Cons
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Arsenic-based compounds are very
fragile in water
Extremely poisonous to most known
life on Earth
Much less abundant in the Universe
Some Earth life already incorporates arsenic in a few organic
compounds.
Creating life, one molecule at a time
→ The field of synthetic biology is focused on the creation of life through
artificial means.
Scientists have:
● Simulated the functions of a unicellular organism in a computer
● Synthesized the amino acids and proteins that comprise our cells
● Built artificial DNA and inserted it into existing cells
We will one day gain the ability to create new life from scratch.
Should we use it? What would we do with it?
Thinking machines
→ The ability for computers to reason is known as
artificial general intelligence. No such system has
yet been developed.
Key questions:
● Is thinking equivalent to computation?
● Would a general artificial intelligence have
rights?
● Can machines be alive?
What we know and what we don’t
In a universe as vast as our own, there must surely be untold
phenomena that we have yet to fathom.
Will they conform to our definition of life?