Hi. It's Mr. Andersen and welcome to biology essentials video number 10. This video
is on abiogenesis in other words how life came to be through natural processes. Now
one of the first people to kind of tackle this you know, really deep question was somebody
named Aristotle. And he came up with this idea of weird, like elements, there's certain
elements and there's an element that can breathe life into inanimate objects. And so that's
kind of reflected here in this, this is from a Roman poet in 20 AD. This is a recipe to
make bees. So if you want to make bees you kill a bull, you build a shed, you place the
dead bull in the shed on some branches and herbs and you wait for summer and then the
decaying body of the bull will produce bees. And so this idea back then was called spontaneous
generation. In other words people knew for example that a seed, if you plant it, would
eventually turn into a plant. But they didn't really understand this in animals. In other
words how we went from nothing to animals showing up. And so they didn't really understand
it and they thought somehow that inanimate objects were creating animate objects. One
scientist actually started taking a look at this, you could say they could figure it out
really easy. In other words, let's say you put a steak out and I leave it there for a
day. Well maggots are going to start to build up on the steak. And so they wondered, well,
was the steak actually creating these maggots? How are they getting there? And so a really
simple experiment would be to take two steaks. Let's have one steak that looks like this
and one steak that we're going to actually cover it. And so nothing can get to it after
we put it out there. So no things like flies can land to put their eggs on it. And so once
we did that then we figured out that life wasn't coming from life, life was coming from,
inanimate objects, it was actually coming from life. And one of the most famous experiments
is Pasteur and we'll talk more about him when we talk about bacteria and his arrival of
the Pasteur Flask and really saying that spontaneous generation is not true. In other words you
don't create life this way. So what did that leave unanswered? It left unanswered, how
did life come to be on our planet? And so scientists have been working at this for hundreds
of years, but especially in the 1900s. They had really a few studies that showed us how
life could come from non living material. In other words how we could get life from
nothing. And so let's get started. First of all most scientists agree that it just didn't
happen like that, with a snap of the finger. We had to go from life, no life to life. And
to get there we had to go through a series of steps where each of those steps make sense.
And so the idea is that we went from chemistry to simple monomers, the building blocks of
life, an example could be amino acids. Those were then polymerized, or added together to
create polymers and made what are called protocells or simple cells that aren't really alive.
And then eventually we have cells and eventually we have life. Now once we have that then natural
selection is going to take over. And then we're going to have the life that we have
today. And we can see that, we talked about that in this whole unit of evolution. Now
the first thing you should understand is that the primitive earth looked a lot different
than the earth that we have today. In other words the atmosphere didn't contain oxygen.
And as a result of that, it was a reducing kind of an atmosphere. Oxygen has a tendency
to really pull on electrons and so life was different back then. And so if we're going
to study this we can't study it in our atmosphere, we actually have to study it in a lab. And
so how do we figure out this progression? Well, we start in science by making what are
called hypotheses. To answer all of these questions we make a hypothesis, which is simply
just a guess and then we test it. Now it's an educated guess and so we think we know
what we're going to find every time we make a hypothesis but one of the first things is
to figure out where life came to be. And we think that, Darwin had suggested maybe it
starts in maybe some warm pond and so this idea of a primordial soup. And a lot of people
are starting to look at the surfaces, in other words maybe it's on clay. It's a great place
where you could actually make some of this polymerization take place. And then what's
the sequence? There are some scientists that are looking at maybe genes showed up first
and others have looked at metabolism. Maybe metabolism showed up. So let's get started.
Let's start by tackling the monomer side. In other word how do we go from chemistry
to simple building blocks of life? And the most famous experiment is called the Miller-Urey
experiment. Stanley Miller here and then Harold Urey over here. And what they did is they
tried to, in the lab, get rid of oxygen and try to simulate what this early earth's atmosphere
looked like. And so this would be the chemicals they thought that were in this primitive atmosphere.
Now you can see there's a vacuum pump over here so we can get rid of our atmosphere and
then we just add energy to it. Energy in the form of electricity in their experiment, but
it's simulating like lightning in this early earth's atmosphere. So why is this famous?
Well it's famous because they stuck their probe in here or they stuck their probe in
here and they found the building blocks of life. In other words they found amino acids.
Now they found a few amino acids. We've actually looked through their work and found that they
found in these experiments twenty-five amino acids. Now there are only twenty amino acids
used in living things and so they found that you could go from simple chemicals or chemistry
to monomers which eventually could become polymers. Okay another thing interesting in the
Miller-Urey experiment is that the amino acids that showed up right away are old amino acids.
In other words, they show up in the latest universal ancestor. In other words the one ancestor
that's shared by all organisms. If we look at the most ancient organisms on our planet,
in other words those that show the most DNA that's shared by all living organisms, we
find that those genes actually code for the amino acids that were found in the Miller-Urey
Experiment. And so this is showing, evidence showing, that life could have formed abiotically.
Now once we go from monomers, the next step is to go from a monomer to eventually a polymer.
In other words amino acids are the building blocks of life but they're not life. What
is life made up of? Life is made up of proteins. And so how do we go from simple monomers to
polymers. Well, first we have to figure out where that could occur. A lot of scientists
think it started in some kind of a primordial soup. Some scientists think it started in
thermal vents. It was probably shielded from space because we'd have a lot of radiation
that would quickly break down any of these polymers. The next thing is to figure out
what's the sequence of events. Early studies, most people thought that RNA was showing up
first. In other words we had nucleotides which are eventually building into RNA. And that's
shared by all organisms. So a lot of scientists think maybe that showed up first. And so we
had this hereditary material that's passed from one to another. But a lot of scientists
are now looking at metabolism and finding that things like the Kreb's Cycle, that's
what this is, that it's shared by almost all organisms. So that means it goes way back
to that latest universal ancestor. And so which of these right? Well there is fields
of science that are studying both of these ideas and the answer we're starting to realize
is probably a combination of the two. And so the tricky part about figuring the origin
of life is that they didn't leave really good fossils, these first life forms didn't leave
great fossils. And so we don't have super evidence of that. One thing I know is true
that once we go from these protocells to the first cells then natural selection is going
to take over. And once we have Charles Darwin's mechanism for evolution take over then it's
really going to start rolling. And so what were these first life forms on our planet?
Well the first fossil evidence are what are called stromatolites. And so these are rock
taken, this is from Glacier National Park, and so stromatolites formed really ancient
in our life and they're essentially bacterial gnats. These are some stromatolites that are
forming today in Australia. And so what you have is bacteria forming up on the top. You
have sediment forming on top of that. And then you have bacteria forming on that. And
it eventually builds up like this and you can kinda see that built up pattern like this.
And so once life shows up which is 3.5, 3.8 billion years ago then natural selection is
going to take over. And I'll talk more about specific evidence that scientists are grabbing
on to to kind of test those hypotheses in the next podcast. So I hope that's helpful.