Lecture 1: Life: How common? What is it? How can we find it? Takeaway messages: –Microbial life probably widespread –More advanced life not so certain –No definite proof as yet –Difficult to define what it means to be alive

Life on originated very early on BYA Impacts could have been frequent Life may have originated more than once Inevitable, given the right conditions?

Right conditions are common Basic for Life As We Know It: –Liquid Water –Concentrated supply of organic material –Appropriate energy source Water fairly abundant; need to be properly placed relative to star C, H, O, N, P, S all relatively abundant Large fraction of stars in the Galaxy provide steady, long-lived source of energy

Life can thrive in forbidding environments Microbial life found in: –Hot springs, hydrothermal vents on ocean floor, in salty, alkaline, or acid solutions –Even in radioactive waste dumps! Extremophiles tell us that life can thrive, maybe originate in places than we used to think impossible

Yellowstone Hot Spring

Complex organic molecules found all over the Galaxy Radio astronomers (1950-today) have found > 100 molecules in interstellar space Comets, meteorites even larger inventory –Include fundmental building blocks of life –Murchison & other meteorites: amino acids, nucleotides, sugars

Molecular clouds

H2 hydrogen CO carbon monoxide CSi carbon monosilicideCP carbon monophosphide CS carbon monosulfide NO nitric oxide NS nitrogen monosulfide SO sulfur monoxide HCl hydrogen chloride NaCl sodium chloride KCl potassium chloride AlClaluminum monochloride AlF alum’m monofluoride PN phosphorus mononitride SiN silicon mononitride SiO silicon monoxide SiS silicon monosulfideNH imidyl radical OHhydroxyl radicalC2diatomic carbon CN cyanide radicalHFhydrogen fluoride CO+SO+ CH CH+ Molecules with Two Atoms

CH3C2H methylacetylene CH3CHO acetaldehyde CH3NH2 methylamineCH2CHCN acrylonitrile HC4CN cyanobutadiyne C6H Molecules with Seven Atoms Molecules with Nine Atoms CH3)2O dimethyl ether C2H5OH ethanol C2H5CN ethylcyanide CH3C4H methylbutadiyne Molecules with Nine Atoms (CH3)2CO acetoneCH3C4N?cyanomethylbutadiyne NH2CH2COOH? aminoacetic acid

Seeding of life from planet to planet Martian meteorites found on Earth –Kicked off by impacts, captured by Earth Study of meteorites + analysis shows primitive organisms could survive Once started on one planet, life could spread to all hospitable environments in that planetary system

Many, even most stars have planets (we think) Natural result of star formation Protoplanetary disks common around young stars, protostars Debris disks seen around more mature stars Astronomers (UCB, etc) have found many (200 +) planets already

Lots of stars --> Lots of planets 10,000,000,000 stars in Milky Way 10,000,000,000 galaxies in known U. 10--followed by 19 0’s = number of stars in the U. Even if a tiny fraction have planets, that’s a LOT of planets

Life commonplace in U. Given right conditions, life inevitable, right conditions found everywhere, life can live in much more hostile environments than we thought,complex organic molecules easily formed, planets are abundant So if we look, we’ll find it (eventually)

New field: Astrobiology What are the general conditions needed for life to appear? How common is it (really)? Where will we find it, and how? What will it be like? HOLY GRAIL: Find SOMETHING biogenic and NOT from Earth

What does “alive” mean? Tough question. So far has eluded the best of them. Is it like pornography: Can’t define it, but you know it when you see it? –Doesn’t that beg the question?? Self-replicating? Not enough. Most will agree: to be alive a system must EVOLVE to adapt to its environment. Darwinian evolution --> Self-replication, selection, mutation

How about digital life? The Ancestor: 80 byte machine code Self-replicating Ancestor-->Daughters-->etc = making copies of the genetic code Random mutations (1-->0 or 0-->1) Fitness criteria-->compete for memory space Q: Is it alive??

Tierra home page:

Don’t ask what it IS, but what it DOES? Life METABOLIZES: interacts with and changes its immediate (maybe even global) environment Certain substances taken in (through membrane), energy extracted, other chemicals exhausted Changes to environment can be small and local up to massive and global

Some changes due to metabolism Composition of the atmosphere Alters isotopic ratios Changes balance of enantiometers Affects relative abundances of organic molecules Even extinct organisms leave trail: chemical, mineralogical, morphological

Familiar example: O2 we breathe Earth’s atmosphere is way out of chemical equilibrium All the molecular Oxygen should go away (oxidizes) in ~ 4 Myrs What’s the source of replenishment? LIFE, primarily MICROBES Alien scientist looking at Earth would immediately suspect planet might be inhabited

Solar system vs extra-solar searches Quite different –Solar system searches much more detailed, primarily local –Looking for life outside the SS much cruder-->look for global biomarkers In both cases: “follow the water” Both cases require big investment

Evidence for water on Mars?

Lecture 1: Life: How common? What is it? How can we find it? Takeaway messages: –Microbial life probably widespread –More advanced life not so certain –No definite proof as yet –Difficult to define what it means to be alive