Lecture 4
Where we left off: Chirality (and homochirality) People like to think that racemic vs. homogenous mixtures is the difference between biological and non-biological materials, but this is flawed. - doing a chemical reaction w/o other chiral molecules produces racemic mixtures
How did chirality arise? - there are a number of possible ways
Non-natural amino acids found in Murchison; 50-60 different kinds of aa’s, total, found.
Disteric isomers – two chiral (steric) centers.
Chromatography: from original observation that a water drop separates out the pigments in ink on paper. Now this term is used to describe any analytical technique that separates out the components of a sample.
Meteorites not only have non-terrestrial amino acids, but also non-terrestrial abundance of elemental isotopes.
Left-handed amino acids can adhere preferentially to one face of a calcite crystal, while D aa’s adhere to an opposite face. This creates a very slight excess of L aa’s.
Clays are generally acidic; when combined w/small molecules, can make more complex molecules.
Fischer-Tropach synthesis produces molecules with longer chain. (South Africa was trying to figure out how to synthesize petroleum, since the trade embargo against them at the time – because of the rest of the world disliking apartheid – was denying them petrol, but they had an abundance of natural coal and other valuable resources, so they were playing around with FT reactions.)
IDP: interplanetary dust particles: constantly bombarding Earth
It would be hard to synthesize RNA in its entirety in a totally a-biological environment; but people have been able to synthesize its components abiologically. - borate might have been abundant on the early Earth; it stabilizes the formation of ribose - you can make membranes with amphiphilic molecules in a test tube
Panspermia It’s a theory that during the period of heavy bombardment, life might have originated on Mars but gotten transferred to earth when a catastrophic meteor hit Mars, devastating it, but seeding it with the tools for life which were ejected back into space and hit Earth. - transfer of rocks between Mars and Earth does happen; happened a lot more often in the period of heavy bombardment
The Antiquity of Life on Earth
- Less crust; surface substrate that life could colonize - The conditions conducive to metabolism, replication, and natural selection, might have been periodic and interrupted.
We can use chemical signatures to learn a lot more than we can just by looking at things.
N. Pole, West Australia, is one of the hottest places on earth – so don’t be fooled by the name! - filamented, graphite microfossils preserved in a silicate material like glass (chert). They look like some kinds of modern bacteria; about 1 micron wide, 20 microns long. 3.5 billion years old. Come from a rock called apex basalt - ?! It is a volcanic deposit, but that’s not the entirety of the rock composition; seawater moving through deposits silica.
Phanerozoic: obvious life period Proterozoic: prototype/early life (no/very subtle fossil record for this period, we just think it probably existed) Archean: rather hellish
Those bacteria-like fossils are from the Archean period.
Landscape of this place: grass that has silica in it to prevent animals from eating it! Ouch. Outcroppings of basalt; low hills and outcroppings of chert. Chert is very tough, more resilient to weathering than basalt. Oldest microscopic fossils come from the riverbeds around chert.