Today, we hold up a delicate, almost invisible,
shield. The University of Houston's College of
Engineering presents this series about the machines
that make our civilization run, and the people
whose ingenuity created them.
In the play, Hamlet gazes at
the sky and says,
... this most excellent canopy, the air, look
you, this brave o'erhanging firmament, this
majestical roof fretted with golden fire, ...
That excellent canopy of air is
impossibly fragile and small when we look over our
shoulder to see it from space. If breathable air were
shown to scale on the globe in your study, it'd be a
hundredth of an inch thick. The cloud cover we saw
from the moon is so thin it could be painted on
Yet compare Earth with the moon, whose surface has
been pitted and hammered into dust by meteors.
We've been less touched by all that falling iron.
Our fragile canopy reshapes the damage done by all
that falling iron. It absorbs and burns the smaller
stuff before it can reach us.
Breathable air, about three hairs thick on your
globe, is a powerful shield against more than
meteors. It has a complex chemical structure. It's
mostly oxygen and nitrogen at sea level, but it
becomes richer in CO2 and ozone higher up.
Ozone is a molecule made of three oxygen atoms. It
forms a gossamer-thin layer, 30 miles up, that
screens out ultraviolet radiation. Without ozone,
that radiation would kill off our nucleic acids and
make life impossible.
Visible light has only a slightly greater
wavelength, but ozone lets it through. And life
would also be impossible without that visible light
High-altitude carbon dioxide caps off the
atmosphere like a greenhouse window. Visible energy
from the sun passes through, and Earth absorbs it.
When Earth reradiates that energy as
long-wavelength infrared energy, the CO2 won't let
it back out.
The greenhouse effect is no theory. It's an
absolute necessity. It keeps Earth warm enough to
sustain life. The only question is, "Will we let
the balance of carbon dioxide rise to the point
where our atmosphere becomes a sauna bath?"
So we're back to that unhappy Dane, Hamlet. His
speech about the air continues. "Why," he cries,
it appears no other thing to me than a foul and
pestilent congregation of vapours.
The witches in Macbeth pick up that same
theme. "Fair is foul, and foul is fair: Hover through
the fog and filthy air." Macbeth and Hamlet forgot
that they were responsible for their lives, and the
air around them seemed to turn foul and pestilent.
That's something for us to remember. Our air may be
a most excellent canopy now. But it has fallen onto
our hands to sustain that preposterously thin
membrane -- so that it can sustain our life and
shield us from hostile space.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds