We've looked at the building blocks Of the origin of life and thought About some of the processes by which Early life might've come to be. But another question is, where did this
occur? Where did these early reactions occur? Where are plausible environments where the
origin of life might've happened? Well, in order to answer that question,
we'll 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 the absence of membranes, those early
molecules that we need to assemnle 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 the 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, Its worth reading it out, its 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 salts, light, Heat, electricity etcetera present, that a
protein compound was Chemically formed ready to undergo still
more complex changes. At the present day such matter would be
instantly devoured or absorbed, Which would not have been the case before
living creatures were formed. Darwin's warm, little pond has become
rather an iconic Image of where the origin of life may 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 or what
those environments might have looked like? Let's have a look at some of the
environments That people think the origin of life could
have occurred. One possible environment is deep sea
events. These events, on the bottom of the oceans,
were reducing fluids, hot Fluids, are gushing up from the crust of
the earth into the oceans. These fluids contain iron and sulfa, 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
iron and sulfur complexes May be a remnant of early life on the
Earth. Alkaline deep sea vents are thought to be Particularly favorable places for 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 And the rocks that have formed around the
edges of These plumes of material that 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 events. Another possible location it impact
creators. Asteroid and comet impacts onto the early
earth Were much more common than impacts events
today. And in these environments, they may have
been Places where early chemical compounds
require 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 rocks, Providing a source of energy for chemical
reactions. And secondly, that heat can create
hydro-thermal cells, In other words, circulating water through
the impact crater. That circulated water could have 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, while the
energy that came from the Impact, creating an environment where
early chemical Compounds could form inside the impact
crater. As the impact crater cooled down, so
conditions Would become more conducive to complex
chemical compounds to assemble And form inside the crater, as
temperatures became less extreme. So asteroid craters are yet another
possible location for the Formation of early compounds and their
assembly into early life forms. Yet another environment that people have
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 early chemical reactions could have
occurred to form the Building blocks of life and ultimately
more chem, complex chemical compounds.
A bit like the hydrothermal vents, yet Another location, could be volcanic hot
springs 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 Be much like the deep sea hydrothermal
vents, source of Energy would have been hot fluids coming
from volcanic regions In the crust and 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 or circulate into reasons that
were cooler, that Would have been conducive conditions for
complex organic compounds, Ultimately cellular material to have
formed in these hot springs. Here is another very interesting idea of
how the Early blocks of life might have formed in
bubbles. And the idea here is, the volcano is Erupted under the sea, releasing gasses
enclosed in bubbles. And these gasses might have included
hydrogen, methane, Carbon monoxide and other types of
reactive gasses. The gasses concentrated inside the bubbles Then reacted to produce simple, organic
compounds. These bubbles would 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 sunlight, creating more
complex organic compounds. And eventually, these complex organic
compounds would have Rained back into the ocean as rain drop
and Rejoined 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 organic
compounds Could of been delivered from outer space
in meteorites. So there are other possibilities other
than some of The environments we have 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 scientist get very focused on one
particular enviroment, it's Not surprising people to research on
volcanic environments or impact Creators or for example, production of
organics in early sea water. But it's quite possible that every one Of these environments was 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
environments in which it evolved? Is there anything about the biology of
life That tells us where it might have evolved? But it's very interesting that some of the Most primitive micro organisms, at least
some of The most deep branching as we call them Micro organisms seem to be the most
ancient. A heat loving micro organisms, thermo
files, Literally heat lovers. These micro organisms grow in volcanic
vents and also in deep sea vents. And there 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 asteroid and Comet impact and because the volcanic
activity Which 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. Micro organisms that were capable of
surviving Hot conditions on the early Earth, but not Necessarily the earliest organisms that
represent 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 the early
reactions For life on Earth might have occurred. Now one possibility is in ice sheets. Water has an interesting property that
when you freeze it it Tends to exclude salts that collect in
boundries between ice grades. Here you can see an image of some ice Crystals between them, the boundaries
where salt might collect. And in those boundary lands we Might find concentrated chemical compounds
where early Reactions could occur. Of course, at low temperatures, chemical
reactions occur Much more slowly than at higher
temperatures With Many, many years of with these reactions
to Occur, maybe ice sheets on the early
earth. Where, where the place is. Where early life could have evolved. Now we have no evidence of coarse that
early life evolved in ice Sheets, or the possibility that early
chemical Compounds would have formed in ice sheets. But reminds us that we need to keep an
open Mind about the possibilities of the early
origin of life. There may be some very quite unusual Environments that we think are not
plausible locations For 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 have 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've been a giant pre-biotic 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. [BLANK_AUDIO]
