Chapter 17. The origins of life and Precambrian evolution

EVOLUTION/LECTURE1
organic molecules, such as RNA, is arguably the point at which non-living matter
came to life
4.2.- The hypothesis that an RNA molecule could replicate itself, serving as a simple
proto-organism, is testable. If the hypothesis is correct, then we should be able to
make a self-replicating RNA molecule in the lab. This has not been achieved today,
although a great of deal of research is currently being conducted in this field.
II: How do we get to RNA:
5.- The problem of moving from an abiotic to a biotic
environment
5.1.- The RNA world has many attractive features, and it solves the problem of having
to propose the advent of proteins before DNA existed to encode them. But an RNA
world come with troubles of its own. Some critics have claimed that it simply
pushes the problem of the origin of self-replication one step back. The issue
here is simple: How could any RNA sequences come into being from an abiotic
environment.
5.2.- The general consensus is that the RNA world was probably not the first
self-replicating system. This is because the likelihood of making RNA abiotically
is too minute (see below heading 8 of this lecture) . The first issue that we need to
address is how information-containing biomolecules were made from simple
inorganic compounds. Where did these molecules come from
6.- Where did the stuff of life come from
6.1.- On September 28, 1969 a meteor entered the Earth's atmosphere over the town of
Murchison, Australia. Soon after, scientists collected some of the meteorites and carefully
brought them back to the laboratory for chemical analysis. To their astonishment, the
analyses showed that organic compounds were present in the interior of the rocks.
In particular, the amino acids glycine, alanine, glutamic acid, valine, and proline were
found in significant concentrations. These amino acids are among the ones used by
modern organisms to make proteins.
6.2.- The amino acids they found were racemic; that is, they included roughly equal
proportion of the D- and L-stereoisomers. By contrast, biological amino acids
are almost purely of the L-form, and thus terrestrial life could not be the source of
the compounds the researchers found in the meteorites
6.3.- Why were the Murchison meteorites significant The biomolecules of life, as well
as their likely precursors, all require the elements carbon, hydrogen, oxygen, nitrogen,
sulfur, and phosphorus in large amounts. If these building blocks could have
been synthesized on the primitive Earth, then presumably they would have been
available for condensation into larger biomolecules. But if they could not have been
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