I wrote this poem about Snowball Earth for the Pacific Science Center’s Polar Science Weekend. Usually I take considerable enjoyment in putting as many obscure and multi-syllabic words into my poems as possible, but in this case I was trying for a younger audience.
I. THE FREEZE, or, Ice-Albedo Feedback
A long time ago, in a place not so far
On the third planet out from a middle-sized star
A watery world, all flecked blue and white
Where conditions would shortly be perfectly right:
The gases that made up the atmosphere changed
As the continents gradually got rearranged
Reflecting more sunlight back out into space
And allowing heat out at a speedier pace.
As the planet cooled down, ice crept toward the equator
And the sunlight reflected grew greater and greater
And the planet cooled more and the ice grew still faster
And the ice sheets and glaciers were vaster and vaster.
When the tropical seas fell beneath the ice pack
It was clear from that point there was no turning back.
The planet was wrapped in a blanket of ice
So thick it could swallow the Space Needle—twice.
It looked like a snowball, so shiny and white
And therefore it reflected most of the sun’s light.
With no light to absorb, it stayed snowy and cold
Till this super-Ice-Age was millions of years old.
II. THE THAW, or, CO2 to the Rescue
But—volcanoes! Undaunted by ice, they don’t care
They just keep spewing lava and gas in the air
With the oceans iced up, gas had no place to go
And so, though the progress was terribly slow
Greenhouse gases built up for a very long time.
Very slowly, the temperature started to climb.
We don’t know all the details (we’re still finding out!)
We do know the ice melted—of that there’s little doubt.
For the planet was Earth, as you no doubt have guessed.
Ice now sticks to the poles (perhaps taking a rest.)
Though the Sun’s now too warm to let Earth freeze again
Earth-like worlds around other stars might well have been
Sealed up under the ice, like we were long ago.
Perhaps some worlds still lie under miles of snow.
There could even be life, waiting for things to warm
Or well-suited to cold with a strange alien form.
But this story I’ve told of seas dark and snow pale
Is just a small part of a more complex tale
For water and ice come in other shades too
From near black to snow white to umpteen kinds of blue.
So the thing I’ve been working to find out so far
Is: what makes ice and snow be the colors they are?
III. LIGHT AND ICE, or, Why Things Work This Way
Two ways that light works are the main things that matter:
We science types call them absorption and scatter.
All things absorb light, but some don’t absorb much–
things like air and Saran Wrap and windows and such.
The more “stuff” light goes through, the less light is left
So you’ll get more absorption from things with more heft.
And some things allow only certain shades through
Like ice, which absorbs red but still lets through blue.
That’s why glaciers are blue, and not red or green
(Or some times they’re a nice sort of aquamarine.)
So that’s why ice looks blue, but then why is snow white?
Snowflakes are just miniature ice crystals, right?
Indeed, snow is just ice in the form of small flakes
But what makes it unique is the shape that it takes.
See, when light hits a surface, it changes direction.
(You can see this yourself with a moment’s inspection:
Put a pencil in water—it looks bent, right where
It comes out of the water and into the air.
It’s not really bent, but the light you see is.
That’s what we call refraction in this science biz.)
So every time light hits a snowflake, it bends
And with lots of snowflakes, that beam of light ends
Up bouncing around and around ‘till it goes
Back out into the air and away from the snows.
That’s why snow looks so bright—any light that goes in
Will quickly be scattered right back out again.
This works much the same for light red, blue or green
Which is why snow looks white. (But, as you may have seen
Light that goes through enough snow will look a bit blue
Because snow’s made of ice, and it can absorb too.)
There are many more ways to change ice’s color
Ice is brighter with bubbles, while dust makes it duller.
And there’s probably ways that we haven’t found yet
So we’re out there looking for new ones, you bet!