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Lecture 9a - Living on a finite planet
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En provenance du cours de University of Arizona
Biosphere 2 Science for the Future of Our Planet
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Life and Resources in Space - Should We Go There?
When will humans live beyond Earth’s gravity? Module 9 is a fascinating and inspiring journey into space. Ignite your imagination as you learn about space tourism, asteroid-mining, moon elevators, robotic space explorers, and Mars colonization. While focusing on space, this module is sure to reaffirm your appreciation of Planet Earth. With Dr. Chris Impey, Associate Dean UA College of Science, UA Astronomy.
Rencontrer les enseignants
Kevin E. Bonine, PhDDirector of Education and Outreach
Biosphere 2
[MUSIC]
This is the massive open online class science for the future of our planet.
I'm going to present the last module in the course, called Life and
Resources in Space.
My name is Chris Impey.
I'm Associate Dean of the College of Science.
And also a university distinguished professor in the Department of Astronomy
at the University of Arizona.
There are going to be five parts to this last module in the course.
And we're going to start with living on a finite planet.
One of the reference materials for my part of the course is going to be
a book I wrote just about two years ago called Beyond, Our Future in Space.
Because in this part of the course we're going to take you far beyond the biosphere
and far beyond the Earth to understand what it might be like to live in space.
What the challenges would be and why we'd want to do that at all.
So I'm going to be taking you on a journey.
[MUSIC]
In the first part of this module,
we're going to be trying to understand how humans spread around the planet.
And have the curiosity that led us to leave Africa 50,000 years ago is the same
curiosity that's driving us to leave the Earth and explore far beyond our planet.
We're going to recognize the complexity of the biosphere and its interconnectedness.
And also that our planet, as limitless as it appears, is actually a finite resource.
And we're also going to look at the population growth in the history
of our planet that leads to the idea of a carrying capacity for the Earth.
And the fact that we might indeed run out of space and
run out of resources to live on this world.
The urge to explore.
A remarkable thing in human history is the way humans spread across
the planet after leaving Africa about 50,000 years ago.
This map is based on DNA evidence from hundreds, perhaps a few thousands humans,
showing how different cultures spread over the planet.
The arrows show the migration from Africa through Asia into Australia,
and eventually, and much later, into the Americas.
Notice how quickly humans spread across the world,
essentially going from the Siberian land bridge across to North America
down to Patagonia in deepest South America in just a few thousand years.
That's just a few hundred generations.
An extraordinarily short time for hunter gatherers with no resources and
no technology.
Humans are the only species that moves in large distances across the planet,
not for the need of resources or food, but because we want to.
Obviously, those people passing through the Californias
went through Southern California where the temperature is very nice.
The beaches are extremely pleasant.
And you might look at this map and wonder, why didn't they stay there?
Why would they head from the frigid north to the equally frigid south part of
South America?
Well, it's driven by curiosity.
Humans have always been tempted to go beyond to the next valley,
to explore into that dark cave to see what lies just beyond.
And I think that same urge is what leads us to travel in space,
even when it's a very difficult thing to do.
This premise now has some genetic information and evidence to support it.
This is a graph based on genetic data of ancient cultures.
And it essentially correlates the proportion of a single gene or
variation of a single gene, an allele, with the amount of
distance that these tribes migrated in thousands of kilometers.
And what you can see is that this single variation of a single gene correlates with
how far humans traveled in early parts of the history of human culture.
And so this, of course, has been dubbed the explorer gene.
Now, biology is far too complex to reduce human curiosity or
migration to a single genetic component.
But this is fascinating data and implies that curiosity,
exploration, potentially at risk to the human,
because this is dangerous activity, has a genetic component.
You can see that the natural occurrence of this allele in the human population is
about 10%.
And that makes sense.
If this gene was absent, then people would not be driven to explore.
They'd get too comfortable with their situation.
And when circumstances or the environment change,
they would be susceptible to being wiped out or losing their food source.
On the other hand, equally you can imagine that if this explorer gene,
as it's called, was present in half the population or more, then too many people
would be venturing off and taking risks, and the tribe might die and not survive.
So there's a sweet spot here.
This same gene in modern human culture has been correlated with risk seeking
behavior.
This allele is present predominantly in people who jump out of airplanes and
fly parachutes and do hang gliding and various risk taking activities.
And it is also present in people with ADHD, attention deficit disorder.
So some correlations with this allele are considered dysfunctional attributes
of humans.
But the underlying curiosity or restlessness that associates with
this genetic component is I think a basis for our exploration of the planet.
And so we have our planet, suspended in space as seen from the moon.
We only first got to appreciate the Earth in 1968 when
the first humans in Apollo 8 left the gravity of the Earth.
Remember, the first humans ever to leave the Earth's gravity, not until 1968, and
to get to see it hanging in space and to recognize the fragility of the atmosphere.
A slender sheet of air that keeps us alive.
A beautiful planet.
The astronauts were struck by it and
wrote almost poetically about it to their families and friends.
This is the Earth as we know it.
This is the biosphere that sustains us.
And notice that it's situated in an extremely hostile environment.
The vacuum and obliterating cold of deep space at almost absolute zero.
The next thing we need to understand about the Earth which is apparently clear in
ecosystems, science, and biology in the last century,
is that we live in a complex interconnected biosphere.
Biology and ecology have connected,
no single scientific discipline can spend these interlocking attributes.
And in fact, the biosphere itself as an experiment in science
is an example of the interconnectedness of nature on different scales, and
the fact that different scientific disciplines have to talk to each other and
understand each other.
And so on the Earth, we can see a range of scales all the way up to the biosphere
itself acting as a single interconnected system moving down
to the system of a forest or individuals in the forest or individual organisms like
a tree in the forest, which is respirating and transpiring and part of the forest.
We can continue down in scales to an individual part of a tree,
which has its own biological function
which is part of the biological function of other components of the tree.
And then down to the tissue, and the cells themselves, and the different cell types,
about 50 different cell types in living biological material.
And then the smallest sub-components, the atoms and molecules.
Each of these different levels, if you counted them, 9 or
10 different levels of complexity, are interrelated on different scales.
And the relationship between these different levels is the subject of a lot
of modern science.
It's also the source of some real uncertainty as to how these systems work
when they're interconnected in this complex way.
The other thing we know is that the Earth is filling up.
Since the industrial and
agricultural revolutions, we've had the capacity to feed more humans.
Modern medicine means less babies die at birth.
And humans live longer, both of which are good things,
but they've led to a literal population explosion.
It's not clear what the carrying capacity of the Earth is,
from its current population of about 7 billion.
It continues to rise, although at a reduced rate compared to 50 years ago.
This next video produced by MPR will show you a nice analogy
of bodies of water filling out vessels and leaking from those vessels to give you
a sense of how the Earth's carrying capacity might be understood.
This is a real concern because as good our technology is,
as good as the revolutions in agriculture have been,
it's not clear how many humans we can feed on this planet.
>> A thousand years ago there were
only a third of a billion people, but we were multiplying.
[SOUND] Now there's 7 billion of us.
How did we grow so much so fast?
Say this glass is North America.
The fuller the glass gets, the more people there are.
Water drips in as people are born.
Water drips out as people die.
Okay, here's the entire world.
Now, let's go back 1,000 years.
The Americas are nearly empty.
Europe and Africa have less than 100 million people between them.
And just like today, most people live in China, India, and the rest of Asia.
For centuries, things stay pretty much the same.
Births are cancelled out by deaths.
Women are having lots of babies, but most babies die before they grow up and
have families of their own.
We don't reach 1 billion until 1804.
[SOUND] But things are changing.
Better medicine and
better agriculture are starting to slow the leak from the bottom of the glass.
People still die of course, but more babies grow up and
have babies of their own.
Lots of babies.
[SOUND] We've grown from
1 billion to 7 billion.
And it only took 200 years.
Will we keep going like this?
Probably not.
The UN says we'll level out at 10 billion by the end of the century.
So as we continue to grow from 7 billion, the question,
is can the world hold that many people?
Experts can't agree.
It all depends on how well we manage our food, water, and
energy [SOUND]
>> This iconic and
evocative image is called the Pale Blue Dot.
In the 1970s and 80s, Carl Sagan used the Pale Blue Dot as a metaphor for the Earth.
But it started as a literal image here taken by an outer solar system
spacecraft looking backwards through the gossamer rings of Saturn.
And the little dot you see there, the pale blue dot is the Earth.
From a distance of a billion miles away,
it's manifestly clear how tiny the earth is, how fragile, how isolated in space.
And Sagan wrote beautifully and poetically about the responsibility that accrues
to being on the pale blue dot to having the destiny of the planet in our hands.
He also was aware we weren't doing too well with it.
He died before some of the worst issues of climate change and global warming, but
he knew the threats of nuclear weapons, biological pathogens, and
he was aware that technology is a double-edged sword.
It has raised a billion people out of poverty in the last century, but
given us the capability to destroy ourselves many times over.
So the perspective of this part of a course is that the Earth is a complex,
fragile ecosystem that is filling up, and that we have the capacity to harm.
That's the end of this part, and I'll see you in the next video.
[MUSIC]
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