hi I'm Sarah Mauer and in this lecture
we're going to examine what earth looked
like 4.2 to 3.8 billion years ago and
how that could relate to the origins of
life the first thing that you should
know is what the geochemical landscape
of early Earth looked like and so there
was definitely an ocean that was warmer
than today's oceans and that ocean was
probably a little more salty than the
oceans that we have on today's planet
additionally there were land masses that
were likely formed through volcanic
activity or possibly also plate
tectonics although this is not fully
known yet and on these continents we
likely had lakes and ponds that were
composed of fresh water due to
precipitation the other forms of water
might it might have existed in temporary
streams that would occur from different
weather events and additionally all of
these surfaces all of these continents
were simply composed of minerals
different types of minerals that would
have been available on early Earth and
so these mineral surfaces are great
location for things like catalysis and
energy generation that we don't really
have today because everything all of the
minerals on earth now are covered by a
layer of life the different chemical
reactions that were occurring on early
Earth's would have been mixed through a
variety of different processes and so
similar to the things that we see on
earth today there were likely tides
there was mixing between the ocean and
the inland lakes through evaporation
aerosol particles getting sprayed into
the air and floating over to a different
location
we had volcanic plumes that were
delivering molecules across the
continent and then you have things like
hydrothermal vents and deep deep sea
locations where a different set of
chemistry's can occur and so all of this
mixing would lead to a unique chemical
library through a variety of different
equation different reactions that lead
to a diverse set of compounds for
early organisms to be generated origins
of life scientists use these locations
and build what we would sometimes refer
to as a warm little pond that Darwin
first proposed and in these ponds there
is some fresh water that flows in and
hydrates the existing molecules so they
can react together and form complex
biological molecules perhaps this water
evaporates and causes polymerizations to
occur as condensation happens and then
they get rehydrated again and
encapsulated into the first cell
membranes and these first cell membranes
can Harbor early forms of RNA or they
can create different catalytic networks
that feed off of one another and through
subsequent generations they will evolve
into the life that we see today and
where these locations occur whether it's
deep in the ocean or in volcanic craters
or here pictured as an impact crater
it's it's highly debated among origins
of life scientists but we do know that
there was a lot of different
environments on earth where life could
have evolved the energy sources that are
going to build our chemical inventory
are going to come from pretty much two
different places so we have chemical
energy which is going to be in the form
of reduced gases or reactive gases like
h2 gas hydrogen gas we also had a lot of
radioactive material which could have
created complex radiation which leads to
free radical formation and then
interesting carbon chemistry and then
minerals could have served as an energy
source because they're often great
electron donors and so redox reactions
drive most of the metabolic processes
that we have in extant life the other
energy sources that we see are
environmental energy sources and so
those are things like lightning or
ionizing radiation or kind of constant
energy sources from the environment like
a high temperature high pressure
environment in the form of hydrothermal
vents and so
all of these different energy sources
are invoked to create our initial
chemical library the first really good
example of this was the electric
discharge experiment sometimes called
the miller-urey experiment named after
the scientists who discovered this that
if you put an electric spark in there
case through electrodes into a chamber
that composed what we think was Earth's
earliest atmosphere shown here as
methane hydrogen water and ammonia we
end up getting a complex library of
biomolecules which are listed in the
table you can see that glycine is a
large component of the prebiotic soup
that they created and glycine is one of
our essential amino acids and so this is
a very promising mechanism for
generating interesting carbon compounds
we also have alanine aspartic acid
glutamic acid other amino acids and then
formic acid and acetic acid which are
part of the reduced carbon library that
we would use to make early metabolisms
while this version of the experiment may
not be true to early Earth environments
because methane was likely not available
on early Earth if you replace that
methane with carbon dioxide
you get a slightly altered version of
the experiment with different abundances
and slightly different products but you
can still get a diverse library of
chemical compounds that could have been
used to create first life the other
major source of organic compounds is
through interplanetary dust particles or
delivery of carbon to earth from the
solar system so when the earth first
formed 4.5 billion years ago the solar
system was still accreting and all of
these small smaller particles would have
been pulled into Earth by Earth's
gravity and these particles have a
different chemistry and different energy
sources that were available to them in
in space essentially and one of the most
famous examples of this is the Murchison
meteorite which is pictured here
you can see that it had a large number
of interesting carbon compounds
including amphiphiles that could form
membrane structures polycyclic aromatic
hydrocarbons alcohols and even some
interesting aliphatic hydrocarbons that
could have been metabolic components and
when looking at other carbonaceous
chondrites which is just a small
fraction of the total type meteors that
are delivered to earth we see that each
meteor hat or meteorite has a different
chemical library these chemical
libraries are produced because the
reactions in space are going to be
dependent on the types of energy that
hit that particle and so these particles
are composed of water and carbon
monoxide and methane perhaps nitrogen
and when high-energy radiation like UV
radiation hit the particles they form
free radicals which allow for some very
strange chemistry to occur and that
leads to complex carbon chemistry
additionally there's heat and there's
gas phase bombardment and perhaps other
forms of ionizing radiation that could
lead to these very interesting carbon
compounds so was there really enough of
these reactions to actually generate a
complex chemical library that could have
led to life when we estimate how often
these occurred and compiled all of the
different sources of carbon we estimate
that about 100 billion kilograms per
year of prebiotic organic material was
delivered or synthesized on earth during
this time and so we think that there was
definitely enough material to actually
jump-start life and to have a biogenesis
occur