 
 
 
 
 
 
 
Hi. It's Mr. Andersen and welcome
to biology essentials video number eleven.
This is on the origin of life and what science
can tell us about the history of life on our
planet. This is also the last video in this
first unit which is on evolution. When Darwin
was starting to formulate his ideas of evolution
and natural selection in the second half of
the 1800s, another scientist was trying to
answer another big piece to that puzzle and
that's Lord Kelvin. And he was trying to figure
out well, how old is the earth? And the way
he did that is he figured out that the earth
was probably or started as a molten rock or
molten material and then he just used heat
change. In other words how long would it take
for the earth to cool down to the point where
rock could actually form. And the values he
kept getting were somewhere between about 20
and maybe 100 million years ago. And so he
eventually kind of narrowed that down to between
20 and 40. And other scientists at that time
were coming up with similar values. The problem
with that is that Darwin's idea of natural
selection and life coming through this random,
somewhat random process played against the
environment. That just wasn't long enough
time for life to have gone through all of
its different transitions. And so Kelvin was
making two mistakes in his calculations. And
so the first one is he didn't understand that
you could have radio active heating of the
crust. In other words you're going to have
radiation that's going to radiate, it's actually
going to warm up that crust. And the other
thing they didn't understand back then is
convection. That there were convention currents
that were actually warming up the crust. And
so these calculations of in the millions of
years were off. And so it wasn't until the
1900s that we actually got an accurate approximation
of how old the earth is. We know that the
earth is about the same age as the solar system
itself. And so what you do is you figure out
things that were around in that early formation
of the solar system and those are called meteorites.
And so we can date meteorites using lead lead
dating. And we can figure out how old they
are. And so now you just have to find where
those meteorites are. And so this is a meteorite
that we use for a lot of those approximations
of how old the earth was. It's call Canyon
Diablo meteorite. It crashed into Arizona
and they found this years ago. But Patterson,
CC Patterson was the first person to actually
make a good approximation of how old the earth
was. And using meteorites and using this dating
we figured out that the earth now, and this
is kind of our accepted value, is about 4.55
billion years ago. So roughly 4.6 billion
years ago and so that gives us plenty of time
to figure out or go through the fossil record
and figure out how life came to be. And so
what I am going to talk about in this podcast
are the origin of life and specifically what
science can tell us about that transition
from no life to life that we have today. We're
going to use three different threads or three
different domains. The first one is going
to be geology. So we're going to look at the
geologic record. Essentially we're going to
look at fossils and see what fossils, what
secrets fossils can unlock at telling us about
the history of life. Next we are going to
talk about chemistry and that famous Stanley
Miller - Harold Urey experiment or the Miller-Urey
experiment. And we're going to show how chemistry
can answer some of these answers of how life
could be. And then finally we're going to
look at molecular evidence. We're going to
see how there are homologists, remember homologist
means structures that are shared by all of
those related organisms. Homologist molecules
are monomers that have been passed through
time. And it's also going to point to this,
molecular evidence, is going to point to what's
called the last universal ancestor. In other
words what's that one ancestor that's shared
by all living things today. And Darwin talked
about that in The Origin of the Species, saying
that there is one common ancestor all life
on our planet. And so now we have a better
answer if Darwin were around today. First
let's look at the geologic evidence. If we
look back through time so we're saying that life
started maybe 4.6 billion years ago, this
first period of time, and again you don't
have to memorize any of these different names,
but the Hadean Era is the first era. And that's
essentially comes from Hades which tells us
what the earth was like at that point in time.
So it was molten material. We were constantly
getting hit by large structures from space.
And so the whole thing was molten and life
really couldn't exist during that period of
time. What's interesting is the point at which
life could actually exist, it shows up. And
so life starts here. There are going to be
approximates, somewhere between 3.5, 3.8 billion
years ago. Some of the first life that we
find on our planet are in these fossils called
stromatolites. And it's essentially a bacterial
or something similar to a bacterial mat that's
laid over time. And so we can date that rock
and figure out that first life started about
3.8 billion years ago but it's prokaryotic.
If we move forward through time, early in
the history of life photosynthesis starts.
And so early in that atmosphere on our planet
there was no oxygen, but once you have photosynthesis
we start pumping O2 into the atmosphere. That
actually leads to some extinctions on our
planet because oxygen is very good at grabbing
onto, it's highly electronegative, and so
it turns a reducing kind of atmosphere into
an oxidizing atmosphere. But eventually life
starts to grab on to oxygen. So things like
cellular respiration use the power of oxygen
to drive that oxidative phosphorolation. So
eventually we have high amounts of oxygen
in our planet and eventually we start to see
eukaryotic life show up. So this is going
to be prokaryotic life. Eventually we have
eukaryotic life. Next thing that we're going
to have is multi-cellular life starts to show
up. Now we're about 1.5 billion years ago.
Eventually we show up with animals and this
Cambrian explosion. We have plants, we have
the dinosaurs and then this would be us way
up here, humans. And so on this whole geologic
time scale humans show up right at the end.
But there is this transition from no oxygen
to oxygen, from prokaryotic life to eukaryotic
life, from single cell to multi-cell, to the
arrival of animals, plants and then this movement,
eventually, on to land. And so where do we
get all of this evidence? It's just geologic.
In other words we're looking at rocks and
we're using absolute dating and relative dating
to figure out how old those rocks are. And
so the nice thing about fossils is they give
us a permanent record of what life was like
on our planet. Next is chemical evidence.
The most famous experiment is called the Miller-Urey
experiment and this is in the 1950s. Stanley
Miller and Harold Urey tried to simulate what
this early atmosphere was like on our planet.
And so they tried to add the material, so
water, methane, ammonia, hydrogen gas, carbon
monoxide. They tried to kind of show what
that early atmosphere was like on our planet.
They added energy in the form of lightning
and then they collected the molecules that
actually came from that. So they could stick
a probe in here and they could grab the organic
material either out of here or out of here.
And what they found is that amino acids started
showing up. So amino acids make proteins and
proteins make us. And so it's the building
block of life. As we start looking at the
chemical processes or the chemical equations
that do that, it's fairly simple to go in
two steps to amino acids. So we could take
carbon dioxide and methane, ammonia and we
can actually make things like, this would
be formaldehyde, hydrogen cyanide, water and
so we can produce these things in a one step
process and then we could eventually use these
or the products of this reaction as reactants
in this next reaction. We can actually make
things like glycine. Glycine is a very simple
amino acid. And so Miller and Urey were able
to show that if you have a sterile environment,
where there's no oxygen, you can actually
make the building blocks of life, which are
those amino acids. Since then an number of
different experiments similar to the Miller-Urey
experiment have shown that we can create the
building blocks. The genetic code as well.
In other words the amino acids, not the amino
acids but the building blocks of RNA and DNA.
Now since that time Jeffrey Bada, he actually
worked in the lab with Miller, has looked
through the vials that Miller did in the 1950s
and found about twenty-five amino acids were
created in that experiment. And the other
interesting thing is that those amino acids
that were created are what are called old
amino acids. In other words, if you look through
the genetic code when we look at the oldest
most ancient genes, we find that those code
for amino acids. And a lot of those older
amino acids are found in this Miller-Urey
experiment. So chemistry shows us how life
could have formed. And then finally we can
look at what we have today which is life we
have today. So again, if you don't exist as
a life form anymore, you are extinct. And
the opposite of that is extant. And so we
can look at extant life forms on our planet.
In other words, life that exists today and
we can find commonalities between that. And
so we've come up with this term, called the
LUA or the last universal ancestor. And so
if we look at the history of life, this tree
of life, it branches into the bacteria over
here and the archaea and eukaryea over here.
But all of life shares some of these common
characteristics. In other words it's based
on DNA. It uses RNA. It uses proteins, ATP.
It uses a lipid by-layer or phospholipids
and finally it goes through cell division.
And so these characteristics are shared by
all life on our planet. And so that suggests
that all life came from this one common ancestor.
If we had multiple genetic codes or multiple
ways of metabolism, in other words ways to
get energy, then that would suggest that we
have multiple common ancestors. But this actually,
molecular evidence is showing us that Charles
Darwin was right. There was one common ancestor
to all life on our planet. Now as a result
of this you can finds some weird things. So
this is a statistic that you could take or
leave. But the idea is that 50% of the DNA
in you and a banana is the same. Now do you
look like a banana? No. But you share half
of your DNA. Now if it was just random chance
since we have four letters in DNA you'd share
25%. And so since we have 50%, that's more.
So what are some similarities that you have
with a banana? Well, you have to use proteins.
You have to make amino acids. You have to
make energy so you're going to use something
like the Kreb's Cycle to do some of that.
You have to make a membrane and so there are
certain things that are shared by all life
on our planet. And those point back to this
most ancient of ancestors. Okay, last thing I
want to talk about is this, and this is kind
of outside the scope of the class but I think
it is pretty interesting. If you look at life,
life we think, if we look back even before
life formed, most scientists now agree that
the universe started with something called
a Big Bang. Maybe something like, I don't
know, 11 billion years ago. So there's this
huge explosion. We get this expansion of the
universe and as we move through time, so this
time is going to be in this scale, we increase
the entropy of the universe. In other words
the universe becomes less and less ordered
or more and more random through time. What's
interesting is as it becomes more and more
random, we actually find life moving in the
opposite direction. In other words we find
life becoming more and more complex, spreading
out and we would say evolving over time. So
all these different strategies. And so how
do we reconcile that? How do we reconcile
that the universe is becoming more random
but we're actually becoming more complex?
Well, we do that at the expense of our universe.
In other words we can actually increase the
randomness of the universe and we can do that
to create more complexity inside us. That's
a little deep. But let me talk about something
that's a maybe makes a little more sense.
This is Ray Kurzweil. And he's a futurist
so he's a really good inventor, invented like
text to speech and optical character recognition.
But he's a futurist and so what he's always
thinking about is the future. And so this
is a plot and it's essentially a plot between
time before now and then the time between
each event. And these are the major events
in the history of life. In other words we
began with life, eukaryotic cells, Cambrian
explosion where animals show up, humans show
up, agriculture, cities, industrial revolutions,
computer, personal computer. And so what he
does is he plots that on a logarithmic scale.
So this is the time before now and this is
the time between each event and what you find
is that it looks linear. But what does that
mean? If you're plotting it on a log scale
and it looks linear that means that all of
this is exponential. In other words the path
of humans to today has been an exponential
curve. In other words it took a long time
for life to show up, but once it did, then
we eventually got eukaryotic multi-cellular
animals and it's going exponential. And so
when we look at the history of life we should
also think about the history of history. In
other words, the history from the Big Bang
to us today. And what we're finding is this
exponential growth. In other words it's amazing
today that you are watching a podcast on the
Internet that can be shared by anybody across
the whole of theplanet. An so what's different here
is that we've stepped outside of that evolution,
which is random chance selected by environment,
and we've actually added something called
culture. And so culture allows us to pass
on information from one generation to the
next and that separates humans from all other
planets or excuse me, animals on our planet.
And it makes us pretty special. And it also
points to a future that is going to be, I
don't know, crazy to say the least. And so
I hope that's helpful.
