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: 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 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 Cons Abundant in the Universe Dissolves many organic compounds and also many metals Can form both acids and bases 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 Cons Both share a similar chemical structure 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?