The Origins of Life

Well, hello, everybody.

My name's Ian Crawford, and I'm a professor

of planetary science and astrobiology

at Birkbeck College in the University of London.

And in this series of mini lectures,

we're going to talk about the new science of astrobiology,

which is the search for life in the universe.

The first mini lecture, we're going

to talk about what life requires,

what kind of environment is needed for life to originate

and evolve, and whether the origin of life on Earth

was inevitable.

So the first thing is to look at this beautiful picture

of the Earth taken from space.

This is taken by the Apollo 11 astronauts on their way

to the moon.

And it shows the only inhabited planet

that we know of in the entire universe.

And of course, the point of astrobiology

is to try and find out whether there are any

more such planets.

So given this, it follows that, Ah, well,

consider when considering what life requires,

what kind of environment life requires.

We're a little bit biased because we only

have one example.

We only have the example of our own planet.

But looking at life on earth, I think

we can say that life needs at least three things to survive.

It needs a source of raw materials,

a source of molecules from which to build

very complicated molecules.

And for Earth life, this is carbon base chemistry.

Life needs a liquid medium, which in our case

is liquid water in which these molecules can

react with each other.

We couldn't have a complicated chemistry

if all the molecules were locked into a solid crystal,

like the organic molecules of which life is made,

have to be able to move and react.

So this requires a liquid medium and on Earth this

is liquid water.

And the third thing is life requires a source of energy.

Many of these chemical reactions require energy

to which have to work nowadays on our planet.

Sunlight is the ultimate source of most of the energy

that life uses.

But there is life on Earth that also uses chemical energy.

And in the earliest days of life on earth,

before photosynthesis was invented,

life probably utilized chemical energy.

So we've got these three things.

Our life requires a source of organic molecules,

a liquid medium, and a source of energy.

Our planet Earth fulfills all of these.

Liquid water is our liquid medium sunlight and chemical

energy provides sources of energy and organic materials,

provide all sources of the materials out

of which life builds its build itself.

Having considered what life requires to survive,

though, it's important to ask how did life

originate in the first place?

Because this may require a different set of conditions.

And frankly, we have very little understanding

about how life evolves from non-life.

But we do have some ideas now.

A long time ago, Charles Darwin was perhaps the first scientist

to really speculate about this, and he

speculated that life might have begun in a what

he called a warm little pond.

This was in a letter to his friend Joseph

hooker, the botanist.

So Darwin speculated that life might have

begun in a warm little pond.

And here in this photograph shows a warm little pond.

This is a warm little pond on the top

of a volcano in Iceland.

And it's one of those environments

that we study as possible analogs for life on Mars

and elsewhere in the universe.

But anyway, it's possible that life might have originated

in a warm little pond where water provided

the means for the solvent for chemical reactions to occurring

heat was provided by volcanic activity and lots of minerals

provided sources of possible nutrients and reactants

in which life might have got started.

So so this is still possible that life on Earth

may have started in something like Darwin's warm little pond.

But there are alternatives.

Ever since we discovered that life

exists around hydrothermal vents in the deep ocean where

really very hot water comes out of the Earth's crust and cools

rapidly when meeting seawater.

And you have these so-called dark Black smokers

where our minerals that are dissolved in the very hot water

crystallize out when they reach contact with cold ocean bottom

water.

Anyway, it's been these environments also

are postulated as possible places

where life may have originated on Earth

and we still do not know which or if either

of these environments were places where life may

have originated on the Earth.

When we consider life elsewhere in the universe,

this is quite an important question,

because whether we're looking for planets

with hydrothermal vents, Black smokers, or planets

with warm little ponds or both.

Or neither are suitable places where life may originate.

I mean, this is something we would

need to understand if we were to understand

how common life might be in the universe.

Given what we know or think we know about the origin of life

on Earth.

It's a legitimate question to ask whether life on Earth

was inevitable.

I mean, it seems to us that we look

around our beautiful planet with such diverse life forms.

And now that we know life has been on this planet

for literally thousands of millions of years,

it is tempting to think it was some sort of environment

in the early history of the Earth that made life inevitable

and that might be reinforced.

And we'll talk about this in the second mini lecture

or the next mini lecture.

When we look at the history of life on Earth.

And it does seem that life did get well started

on the Earth very early.

And so given this, it's tempting to think

there was something in the early Earth's environment

that made the origin of life inevitable.

But of course, we cannot know that as a fact

because we've only got one example.

We now also know there are billions and billions

of planets in the universe.

So for all we know, nature may have

tried to get life going billions and billions and billions

of times and failed every time except on our own planet.

So life might still be rare, even though in the universe,

even though it originated on the Earth so early.

So we do not know whether life, the origin of life on Earth

was inevitable given the conditions on the early Earth

or not.

The only way to address this question

is to go and explore the universe.

The only thing we can do is to study more planets that

are like what the Earth was 3 and 1/2 to 4,000 million years

ago, and see whether life commonly

arises in those environments.