Now we really can only guess about those terms, but
you know, for the first one, when does life form?
We do actually have some information by, based on our
understanding of chemistry and some experiments that we've actually done.
So now of course, you know, what is life is
kind of an open question and you can certainly ask.
You know, is it possible to have the kinds of life that
maybe we wouldn't recognize as being alive, you know viruses are right on
the boundary between what, you know, might be
defined as being alive or not being alive.
But, you know, we're going to put that aside for right now, we're
just going to try and focus on life that, you know, is clearly recognizable.
So for example, what, what are criterion for defining something made of life.
Well if we're going to talk about, you know, the life
that we recognize, it's something that's composed of organic molecules.
You know, chains or rings of carbon or
some other you know very chemically active element.
We certainly expect there to be metabolism, right?
The ability to consume energy.
And of course if you're consuming energy, thermodynamics tells
us you're gotta have to produce waste as well.
So we expect that metabolism is going to be part of a definition of life.
Reproduction, we expect that there should be more, you know, that as time
goes on, you're going to produce more of whatever you started with, right?
That reproduction the replication uh,maybe not exact of you
know the existing beings or existing examples of, of life should be part of it.
Mutation is very important, because if you don't
have mutation, you don't have the possibility of evolution.
So we expect that mutation in some
form should play an important role via evolution.
We expect evolution to be, we believe
evolution should be a fairly universal processes.
And then a sensitivity to the environment, that also ties into evolution.
because you know, if the environment changes, you expect that
you have to respond to it or you die, right.
And one of the things about mutations is that mutations will
create the possibility for organisms to respond positively to their environment.
If you know, the environment gets drier and
you have a random mutation that allows you to
use water better that, you're going to tend to
have your offspring making it to the next generations.
Okay, so here's
the basic criteria.
What do we, what can we do to think about how life actually formed?
Well, one amazing experiment that was done back
in the 1950's, and it's been replicated many times
came from the idea of some scientist asking
what were the conditions on the early earth like.
And would it be possible that those conditions
could lead to the building blocks of our life.
So this is something that was called the Miller-Urey Experiment.
And basically what they did is in a test tube, or
series of test tubes, they built a model of the early Earth.
And so there was water that was being heated by geological processes.
And there was material in the water that you would expect to
find, all the elements that you'd expect to find in the early Earth.
They also had an electric discharge tube.
And there that would create lightning.
And so you know, they basically, you know, put all this stuff in, the water,
the elements, the lightning, turned it on and you know, went away for a while.
They came back in a week or so, and what they
found was this goo at the bottom of their test tube.
And when they looked at it, they were, you know, amazed to find that basically many
of the building blocks, the amino acids that
are needed to form proteins, were already there.
And this really gave the indication that
you don't need much to sort of get the process started.
Now, of course, it's a long way from amino acids to a self-replicating molecule,
but of course, that long way is taken care of, in some sense, by time.
The the stretches of time over which evolution occurs are,
you know, tens of millions, hundreds of millions, billions of years.
And so if you have this goo at the bottom of, you know, of a pool of tide water.
And these
molecules are colliding with each other,
by just, you know, random collisions, eventually
you're going to sample, you're going to
start testing all the different possible configurations.
And some of those configurations may
eventually lead to a self-replicating molecule.
And the interesting thing about that is what you then get is chemical evolution.
Once you have a self replicating molecule, then basically what it does, it eats
up all the other elements or other chemicals in the in the pool and
it dominates.
So you know, once you can start getting self replication
really remarkable things can take into can begin to occur.
