Scientists work everyday to solve the mysteries of the universe.
Some of them go their whole careers without solving one freaking mystery.
But others get lucky.
Or they get creative and they find answers by trying stuff out. In science,
we call this experimentation.
So today we're gonna look at three biological experiments
that changed the world.
Number one:
The Swan-Neck Flask Experiment.
In 1862, Louis Pasteur set out to prove that living things did not spontaneously come into existence.
They had to come from some other living thing.
Now that seems like a no brainer to us
but at the time most people believed in spontaneous generation;
the idea that some kind of vital principle in the air
caused life to just arise out of nothing.
Pasteur was interested in the newly discovered life-form bacteria
and another scientist Lazzaro Spallanzani
had just proven that bacteria could be killed by being boiled
and, if sealed from the air in a container,
would not grow back.
Regardless of Spallanzani's finding though,
critics argued that boiling just
"killed the vital principal in the air inside the container."
So Pasteur invented an apparatus that he called the Swan-Neck Flask.
He designed it so a sterile liquid
could be exposed to the air
but no outside particles like dust or bacteria
could get past the curve in the flask's neck.
He filled the flask with broth,
boiled it and let it sit.
Even though it was exposed to the air,
the broth never became contaminated with bacteria
proving that air itself had no vital principle.
As a result, the theory of spontaneous generation,
"enemy of science,"
was dead,
once and for all.
Number two:
The Blender Experiment.
In 1952, geneticists Alfred Hershey and Martha Chase used an ordinary kitchen blender to show that organisms' genetic information is stored in the DNA.
At the time, it was thought that this information was kept in proteins but to test this
Hershey and Chase used a virus that infects bacteria called the bacteriophage which just consists of a strand of DNA
surrounded by a protein shell. They whipped up two batches of this virus.
One that had a radioactive marker in its protein shell and another that had a marker in its DNA.
Next they let each batch infect some ordinary E.coli bacteria,
then they used the blender to separate each batch of viruses from the bacteria that they had infected.
What they found was that in the first batch the leftover solution contained only radioactive protein.
This suggests that the viruses had left their shells on the outside of the bacteria
and transferred their DNA inside.
In second batch, radioactive DNA was nowhere to be found again suggesting that it was now somehow inside the bacteria.
And sure enough, when they tested the bacteria they found that the radioactive virus had been incorporated into the bacterial DNA,
thus not only showing us that the DNA contains genetic information, it also taught us how viruses infect their hosts.
And finally number 3:
The Miller-Urey Experiment.
Just a year after Hershey and Chase blew everyone's minds,
Harold Urey and student Stanley Miller set out to see if they could recreate the conditions that made Life on Earth possible in the first place.
First, they theorised the chemical makeup of Earth's early atmosphere over 4 billion years ago,
then they mixed those ingredients methane , ammonia , hydrogen and water and a network of flasks connected to a continuous 60,000 volts electrical current.
They found that after a week, most of the ammonia and much of the methane had been replaced by carbon monoxide , nitrogen and amino acids;
the building blocks of proteins and essential components of life.
Today scientists are still debating Miller and Urey's results mostly because they were probably wrong about the chemical conditions of early earth
and because amino acids have since been found on meteorites suggesting that they could been introduced to earth from space.
But since 1953 scores of scientists have recreated this experiment with different ingredients and eventually spark the discipline of Prebiotic Chemistry,
which has become incredibly influential in advancing what we know about the origin of life.
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