Stated Clearly presents: What was the Miller-Urey Experiment? It was once believed
that if you left food out to rot, living creatures like maggots and even rats
would simply poof into existence. The idea was called spontaneous generation.
A series of experiments starting in the sixteen hundreds disproved this idea, and in
the 1800's, a new scientific law was proposed: life only comes from life.
It's true that rats, maggots, and even microbes are far too complex to simply poof into
existence, but in 1859, English naturalist Charles Darwin put forth
the theory of evolution.
in it he showed that under the right circumstances, relatively simple
creatures can gradually give rise to more complex creatures. Given this
information, serious thinkers began to wonder:
Is it possible that simple life forms actually
could come from non-living matter? Not by poofing into existence, but through a
natural, gradual process similar to what we see in biological evolution.
Darwin himself mentioned this idea when writing to a friend: "...but if, and what a big if"
he wrote, "we could conceive in some warm little pond, with all sorts of ammonia
and phosphoric salts, light, heat, electricity and so on present, that a
protein compound was chemically formed, ready to undergo still more complex
changes..." In 1924, Russian biochemist Alexander Oparin published a book
which he titled THE ORIGIN OF LIFE. In it he outlined his thoughts on a gradual
progression from simple chemistry to living cells. He imagined the early ocean
as a primordial soup, a rich collection of complex molecules produced by natural
chemical reactions. In this soup, chemical reactions could take place
eventually producing living cells! At the time
Darwin's warm little pond and Oparin's primordial soup were really just
speculation.
They were founded on a good understanding of chemistry and biology
but they could not be considered legitimate scientific hypotheses because
no one had found a way to test or observe them. Science after all, is the
study of observable facts, and an ongoing conversation about how those facts can
be best linked together.
Cchemical reactions like those proposed by Darwin and Oparin are not expected
to leave an observable fossil record. Without either having fossils to examine
or a time machine to travel back and observe what happened, how good
scientists even begin to study the origin of life? In the nineteen fifties
Stanley Miller, then a graduate student at the University of Chicago, came up
with an idea. We can simulate early Earth conditions in the lab and then carefully
watch what happens. If you can't study fish in the sea,
set up an aquarium! Working with his professor, Harold Urey, Miller designed an
apparatus to simulate the ancient water cycle. Together they put in water to
model the ancient ocean, it was gently boiled to mimic evaporation. Along with
water vapor, for gases in the atmosphere they chose methane, hydrogen, and ammonia.
These are simple gases which scientists at the time I thought were probably
abundant on the ancient earth. They added a condenser to cool the atmosphere,
allowing water molecules to form drops and fall back into their ocean like rain.
The ancient Earth would have had many sources of energy
sunlight, geothermal heat, and even thunderstorms; so they added sparks to
the atmosphere to simulate lightning. The goal of the experiment was not to create
life, but to simply test the first step in Oparin's model: Can simple
chemistry naturally give rise to the complex molecules of life? After running
the experiment for just one week, their ocean became brownish black. Careful
analysis revealed that through a series of reactions, many complex molecules had
been produced. Among these were amino acids, special molecules of life that we
once thought could only be built inside their bodies and living creatures.
This was a pivotal breakthrough in science, so significant in fact that I gave
rise to an entirely new field research now known as Prebiotic Chemistry!
Scientists don't know for sure if the gasses used by Miller really were the
most common gases in the ancient Earth. Because of this, many experienced have
since been done showing that the molecules of life can form in a wide
variety of environments with different starting chemicals and different sources
of energy.
Sugars, lipids, and amino acids have even been found on meteorites. This suggests
that the molecules of life are fored all throughout the antient solar system, and
may be forming right now in other regions of our galaxy! Together these
discoveries tell us that Oparin's primordial soup, and Darwin's warm little
pond, could have easily existed, in one way or another, on our ancient planet.
So to sum things up: What was the Miller-Urey experiment? The Miller-Urey experiment was
our first attempt at simulating ancient Earth conditions, in this case, the
ancient Earth's water cycle, for the purpose of testing ideas about the
origin of life. the Miller-Urey experiment is significant for two main reasons:
First, though it was not a perfect simulation and the early Earth, it clearly
demonstrated, for the first time, that biomolecules can form under ancient
Earth-like conditions. Second, the experiment took what was once mere
speculation, the idea that life may have emerged from chemistry, and transformed a
portion of that speculation into legitimate testable science! Many
questions remain to be answered about the origin of life but scientists from
many nations and many fields of study are now following Stanley Miller's lead.
They're finding ways to turn those questions about the origin of life into
testable scientific hypotheses.
Simulation experiments cannot tell us exactly how life formed in the past, but if
enough of them are done, they could eventually tell us if it's possible for
life to emerge from chemistry.
I'm Jon Perry and that's the Miller-Urey experiment Stated Clearly!
this video was funded by the Center for Chemical Evolution, the National Science
Foundation, and NASA! Special thanks to chemist Eric Parker, he volunteered hours
of his time going over our script, sending us scientific papers, and
critiquing our visuals for this animation. Though we do receive grants from
time to time, Stated Clearly is made possible with financial contributions
from viewers like you! To support us, visit our website statedclearly.com
and click contribute. I'm happy to announce that you can now also support
as on Patreom.com.
So long for now, stay curious!