We've looked at the building blocks of the origin of life and thought about some of
the processes by which early life might have come to be, but another question is
where did this occur? Where did these early reactions occur and where are
plausible environments where the origin of life Might have happened. Well, in order
to answer that question or think about answering it, we first of all have to
understand what we need for an origin of life. Quite apart from those building
blocks, there are three other things that are necessary in order to get an origin of
life. First of all, we need an energy source. We need energy to do those
chemical reactions, to create those building blocks. And, eventually, to
assemble those building blocks Into more complex structures and eventually cells.
We also need a means of concentrating molecules. In an absence of membranes
those early molecules that we need to assemble early membranes and other
chemical reactions have to be able to be concentrated otherwise they'll just
dissipate in the environment. They'll become diluted in the oceans. So we need
environments where. Complex chemicals can begin to concentrate. And finally we need
an environment that's conducive to these complex molecules and their assembly once
they've been made. It's no good having an environment for example that's so hot that
when we assemble membranes they simply fall apart because of the intense heat. So
we need to find environments where the physical and chemical conditions. Might be
conducive to these molecules once we've made them. One of the earliest
speculations about the origin of life was made by Charles Darwin. Who in an 1871
letter to his friend Joseph Hooker, wrote the following, and it's worth reading it
out, it's rather a remarkable speculation. But if, and oh, what a big if, we could
conceive in some warm little pond, with all sorts of ammonia and phosphoric sorts,
light, heat, electricity, etcetera, present. That a protein compound is
chemically formed, ready to undergo still more complex change s.
At the present day such matter would be instantly devoured or absorbed, which
would not be in the case of Before living creatures were formed. Darwin's warm
little pond has become rather an iconic image of where the origin of life might
have occurred. It's certainly a good idea. But based on what we know about
environments today on the earth can we come up with perhaps some more concrete
speculations about what that warm little pond and about what those environments
might have looked Look like. Let's have a look at some of the environments where
people think the origin of life could have occurred. One possible environment is deep
sea vents. These are vents at the bottom of the ocean where reducing fluids, hot
fluids by gushing up from the crust of the earth into the oceans. These fluids
contain iron and sulfur, which is very interesting because In some of the energy
transfer proteins in life we find chemical compounds that contain iron and sulfur.
Some people have speculated that these are in self a complexes, maybe a remnant of
early life on the earth. Alkaline deep sea vents are thought to be particularly
favorable places. The formation of chemical compounds. The source of energy
in this environment comes from the hot fluids coming up from inside the crust.
The concentration of organic compounds could potentially occur in the chimneys
around these vents where they're gushing up into the oceans, in the rocks that are
formed around the edges of these plumes of materials. That's, are being produced in
the oceans. They may be conducive to formation of complex compounds because the
compounds could be dissipated into the oceans or collect around the vent where
temperatures are cooler and where they wouldn't break apart so easily. So we can
see that many Of the requirements for the production of chemical compounds needed in
the origin of life might have been, might have been met in these deep sea vents.
Another possible location are impact craters. An asteroid or comet impacts onto
the early Earth were much more c ommon than impact events today and in these
environments. There may have been places where early chemical compounds required
for the origin of life could have formed. When an asteroid or comet slams into the
surface of the Earth several things happen, first of all it heats up the rock
providing a source of energy for chemical reactions. Secondly, that heat can create
hydrothermal cells, in other words, circulating water through the impact
crater. That circulated water could've provided environments for early chemical
reactions to occur to produce complex compounds. And, the water that collects
inside that impact crater Might be an almost literal interpretation of Darwin's
warm little pond. A body of water heated by that, by the energy created that came
from the impact and creating an environment where early chemical compounds
could farm. Inside the impact crater. As the impact crater cools down so conditions
will become more conducive to complex chemical compounds to assemble and form
inside the crater as temperatures became less extreme. So asteroid craters At yet
another possible location for the formation of early compounds and their
assembly into early lifeforms. Yet another environment that people thought about are
beaches. Beaches are interesting because of course as the tide comes and goes.
Water flows over the surface of rocks. And as the tide goes back out again, the water
inside the rocks begins to evaporate, concentrating chemical compounds inside
those rocks. So perhaps rocks on the edges of beaches were also places where early
chemical compounds could have concentrated and. And early chemical reactions could
have occurred to form the building blocks of life and ultimately more complex
chemical compounds. A bit like the hydrothermal vents, yet another location
could be volcanic hot spring on the early continental land masses instead of in the
deep oceans now on the continents, and the Advantages of these early volcanic hot
springs would have been much like the deep sea hydro thermal events. The sourc e of
energy would've been hot fluids coming from volcanic regions in the crust,
flowing onto the surface of the earth. Chemical compounds would have collected in
these early volcanic hot springs and as some of these hot springs began to cool
down and circulate into regions of. Cooler. There would have been conducive
conditions for complex organic compounds ultimately cellular material to have
formed in these hot springs. Here's another very interesting idea for how the
early building blocks of life might have formed in bubbles. And the idea is the
volcanoes erupted onto the sea releasing gases enclosed in bubbles. And these gases
might have included hydrogen. Methane come outside other types of reactive gases. The
gases concentrated inside the bubbles then reacted to produce simple organic
compounds. These bubbles rise to the surface of the ocean and burst releasing
their contents into the air. These simple chemical compounds, these simple organic
compounds would then drift through the atmosphere and react even further, perhaps
with ultraviolet radiation in the atmosphere from the sunlight, creating
more complex organic compounds. And eventually, these complex organic
compounds will rain back into the ocean as raindrops, and rejoin that process. Again,
forming bubbles and being recirculated to the surface of the ocean, and back out
into the atmosphere. There's no direct evidence for this process as a way to form
the early compounds required for life, but it's a very interesting alternative
possibility for the production of early organic compounds. Of course, we've also
seen that organize compounds could have been delivered from outer space in
meteorites. So there are other possibilitirs other than some of the
environments we've looked at on the early Earth. Yet, another possibility is that
all of these environments Were reactors producing the early compounds required for
life. Many scientists get very focused on one particular environment. It's not
surprising people do research on volcanic environments, or impac t craters, or for
example production of organics in early sea water. But it's quite possible
everyone of these environments is generating organic compounds, perhaps the
whole of the early Earth was a giant prebiotic reactor producing chemical
compounds in different environments, that came together in one particular
environment to produce early cells, an environment. That we don't know the
identity of yet, but early environments would have all been producing, these early
chemical reactions. Can we find any evidence in life for the environment in
which it evolved? Is there anything about the biology of life that tells us where it
might have evolved? What's very interesting is that some of the most
primitive microorganisms at least some of the most. Deep branching as we call them,
micro-organinizms that seem to be the most ancient, are heat loving micro-organizms.
Thermophiles, literally heat lovers. And these micro-organizms grow in vulcanic
vents, and also in deep sea vents And they may be some indication that the earliest
life forms on Earth, were actually heat-loving microbes that lived in hot
environments. We have to be careful though, because the early Earth was
bombarded by astroid and comet impacts. And because of volcanic activity, it was
much hotter than it is today. So it might be that these. Ancient microorganisms that
love heat represents some sort of bottleneck in evolution, microorganisms
that were capable of surviving hot conditions on the early Earth but not
necessarily the earliest organisms that represents the earliest stages of life
when it first evolved. But nevertheless the fact that some of the most primitive
organisms on the Earth seem to be heat loving is rather intriguing. There are
other more intriguing environments that are quite counter-intuitive, where early
reactions for life on earth might have occurred, and one possibility is in ice
sheets. Water has an interesting property that when you freeze it, it tends to
exclude salts that collect in boundaries between ice grains. Here you can s ee an
image of some ice crystals and between them, the boundaries where salts might
collect and in those boundary lines we might find concentrated chemical compounds
where earlier reactions could have ocurred. Of course at low temperatures,
chemical reactions occur much more slowly than at higher temperatures but with many
millions of years for these reactions to occur Maybe ice sheets on the early Earth
where, were the places where early life could have evolved. Now, we have no
evidence, of course, that early life evolved in ice sheets or the possibility
that early chemical compounds would have formed in ice sheets. But it reminds us
that we need to keep an open kind about the possibilities for the early origin of
life. There maybe some quite, quite unusual environments that we think are not
plausible locations for early chemistry, but might turn out To be important as
places for early chemical reactions. So what have we learned in this lecture? Well
hopefully we've learned that numerous environments could have provided plausible
locations for the production of the building blocks of life and we've looked
at some examples of those possible environments. We've learned that these
environments need not be mutually exclusive and different molecules might
have been produced in different places. Indeed the whole of the early earth might
have been a giant Prebiotic reactor. And finally, we don't know how quickly this
happened. Did the origin of life occur within a matter of days, or weeks, or did
it take hundreds of millions of years? This is one of the unsolved questions in
the origin of life and a question that astrobiologists still have to address.