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hello everybody and welcome to video
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number two of evolutionary milestones in
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which we're going to look at the origins
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of the the material um where it came
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from the um the life requires on Earth
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and we're going to look at some
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processes B by which a biogenesis that
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is the origin of life may have occurred
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so let's jump right on in so a key um
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solvent that all life on Earth relies
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upon is water so water is a really key
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molecule and um in order for a
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biogenesis to occurred there must have
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been water around a key source of water
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was infall from asteroids and comets um
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so asteroids and comets such as those
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that are shown um in this image here Cy
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of NASA um are a very very rich source
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of water but there's also the potential
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um origin of water on Earth through the
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degassing of hydrated mantle minerals so
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as Earth cooled down possibly it degased
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releasing water vapor and the relative
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impact of those two potential sources
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for the water on Earth remains debated
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you can find more details of that in the
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um the two sources that I put on the
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slide
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here the other thing that we need for
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life are organic compounds that's
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compound compound that contain carbon
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hydrogen bonds all cells rely on this
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kind of compound compound so where on
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early Earth could these compounds have
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originated from well one source is input
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from space so research over the last few
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decades has shown us that um we find a
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rich repertoire of organic compounds
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many of which are shown on this slide
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here from this Source at the bottom um
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because Mark Sefton um many
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inter interplanetary dust particles
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comets asteroids and meteorites contain
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this wide assortment of organic
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compounds so those compounds could have
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originated by falling into Earth from
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those um extra um extraterrestrial um
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sources and those compounds include
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amino acids nuclear bases methane and
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hydrogen
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so that's a potential source of some of
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the compounds that could have been the
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building blocks of early life the second
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potential source for those organic
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compounds is Earthbound synthesis so the
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synthesis from Simply components of
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those compounds on the early Earth and a
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classic experiment in this area was by
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um uh two scientists in the US called
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uran Miller who um took a series of
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steps to investigate this they sealed
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what they considered to be a realistic
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primitive atmosphere into a experimental
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setup that comprised um hydrogen methane
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and ammonia so that's shown here they
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used water to represent the early oceans
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and they use an electrical spark to
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represent lightning which you would have
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thought would have been quite common on
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early Earth and they just left that
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running for a week cycling around this
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experimental setup at the end of this
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that week they demonstrated that up to
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15% of the simple carbon that had been
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in the um early primitive atmosphere had
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been incorporated into organic compounds
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2% of that had gone into amino acids
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those are the building blocks of
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proteins so that was a really that was a
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key experiment and a really exciting
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discovery that suggested and supported
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the idea that we can create increasingly
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complicated and complex organic
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compounds on Earth nowadays the choice
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of environment that these um two uh
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researchers um made um we don't think is
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necessarily accurate we think it may be
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too reducing the the nature of the early
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atmosphere on Earth remains a matter of
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debate but this experiment in general
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works and shows um the synthesis
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consists of more complicated organic
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compounds in a range of different
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potentially realistic early
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environments so that's where material
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might have come from and then there are
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several theories for the origins of Life
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a biogenesis that exist and for ease I'm
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going to be placing them today in two
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general schools one of those is
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primordial soup as represented by this
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Campbell's primordial soup um a tin can
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now this primordial soup idea is an idea
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of the origin of life that is kind of
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cold and oceanic it doesn't require high
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temperatures and it would have occurred
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in Earth's oceans so what we're looking
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at in primordial soup type theories of
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abiogenesis is the accumulation of
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organic compounds in our primordial
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oceans those could have been then
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concentrated through freezing or
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evaporation um and there therefore
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become uh higher in their concentration
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in our oceans that could lead to
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reactions between our organic compounds
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that lead to increasing complexity it's
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possible and some theories suggest but
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others don't that this could have
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occurred at the interfaces of minerals
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in these early oceans but whatever
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happened these reactions would have
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created bigger molecules they would have
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been a form of
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polymerization some of the these
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polymers that result could have acquired
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functions by chance okay so you just
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create lots of different polymers this
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whole kind of range of different
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potential um organic compounds could
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have existed and as soon as just one of
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those becomes capable of catalyzing its
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own replication then Bingo you have the
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beginnings of life so by catalyzing its
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own replication I mean that it supports
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um chemically uh the creation of more
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copies of itself even if only a tiny
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fraction of those molecules in these
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early oceans um are capable of doing
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that those would become increasingly
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abundant because they're catalyzing
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their own replication and that would
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lead to a primitive form of biochemistry
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and an evolutionary Cascade towards more
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complicated um
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reactions so um that is one potential
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source and if you want to learn more
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about it you should see the reading list
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for this course um which I've linked
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from the Blackboard um site for 22101 if
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you're a student at the University of
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Manchester if not you're welcome to
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email me and I can provide you with some
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suggested reading however I wanted to
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highlight the other theories for how
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abiogenesis occur and they can generally
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be placed into a second school of
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thought which is the metabolist theory
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so these theories of a biog Genesis tend
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to be hot they occur higher temperatures
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and they tend to um be based around a
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volcanic type of origin of early life
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and in these theories um primitive life
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would have been uh metabolic so it would
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have been characterized by a continuous
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chain of self- sustaining chemical
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reactions okay so we could be talking
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about simple compounds such as CO2
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carbon dioxide and Co carbon monoxide in
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the vicinity of mineral Rich
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hydrothermal systems we're talking about
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things like black smokers such as the
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shown in this these images here courtesy
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of the National Oceanic Oceanic and
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Atmospheric
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Administration this is a an example um
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that's not showing many signs of life
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but this is a modern example showing
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that around these hot smokers these deep
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sea hydrothermal systems nowadays we
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have Rich um communities living a vital
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difference between these metabolist
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theories and the ones I introduced
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before um the primordial super ons is
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that here the first life would have not
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had the requirement for informational
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molecules rather we're talking about a
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series of
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reactions those reactions could involve
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in comp complexity and then eventually
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some form of genetic molecules must have
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been Incorporated if this theory is is
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true because life today relies upon
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genetic molecules and how that occurred
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there's lots and lots of ideas about um
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and it remains a matter of active debate
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um but kind of I would note at this
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point the self- sustaining reaction
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chains could have played an important
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role in enriching the Prebiotic soup in
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molecules so these two theories could of
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metabolist and primordial soup could
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actually be complimentary the privity
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that we have to kind of separate things
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into schools of thought is not
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necessarily useful or indeed accurate
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and there could be elements of Truth in
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both of them but those are the two major
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schools of thought by which a biogenesis
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occurred and we are here I'm talking to
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you on this video now so we know that it
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did so let's look in our next video at
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the steps um that may have um followed a
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biogenesis I'll see you there in a few
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minutes time
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take care
