CO2 is denser than air. This is easily demonstrated in class.

Combine vinegar and baking soda together in a beaker to generate the gas. The students will groan. Yeah, we know this already, it bubbles.... Ask them what bubbles, and they will tell you what everybody already "knows"--carbon dioxide.

Now light a candle. As a diversion, ask them what gasses are emitted (CO₂, H₂0), then hold the beaker over the lit candle, and "pour" out the CO₂, leaving the foamy liquid.

A second or two later, the flame dies, as if sucked back into the wick.

What happened?

***

Just a few hours ago, hundreds of dragonflies swooped around us in the dying dusk. A cold front had just passed through, and the critters were feasting on the swarming insects trapped at the bay's edge, where horseshoe crabs have just about finished their annual orgy.

Dragonflies and horseshoe crabs both came through the Great Dying, a quarter billion years ago. Most of life was destroyed in an event far more extreme than the last mass extinction that ended the age of dinosaurs.

Though it's not clear what happened, extreme CO₂ levels likely played a role. CO₂ snuffs fires, CO₂ snuffs life.

This August marks the 25th anniversary of the Lake Nyos disaster--over 1700 humans killed in Cameroon by a cloud of carbon dioxide exploding out of the lake in a 100 yard high watery mountain of foam, as tall as Manhattan's Trinity Church, the gas suddenly released like the effervescence of  millions upon millions of bottles of seltzer.

The heavy gas flowed down the walls of the volcanic lake that released it, a deadly spree, depriving the living of oxygen as it pushed up the lighter air.

Unanticipated, but not unnatural.

Some locals briefly attributed the devastation to Mami Wata, to a neutron bomb, to "strange Europeans...heavy-set, menacing Nordic...motorcyclists" seen just before the explosion. The eruption had been predicted by a healer who himself did not survive.

***

251 million years ago, carbon dioxide obliterated over 90% of the species around at that time. So little plant life grew that there's a "coal gap" in the fossil record--a 10 million year span where no coal was formed. And yet, the dragonfly line persisted, the horseshoe crabs, too.

These ancient creatures once frightened me with their compound eyes, their complex symmetries, their deliberate living, their bodies so perfectly fit for their niches that little has changed in hundreds of millions of years.

In biology, perfect life does not exist. In biology, the environment defines those who are less imperfect.

But if perfection does exist in life, if there are life forms that will continue to see the dying dusk so long as the sun casts its energy on Earth, it might be found in the creatures that share edge of the Delaware Bay, the bizarre ancient forms of the dragonfly, the slow creep of the horseshoe crab.

I do not know how many of us know the story of Lake Nyos, the stories of Mami Wata, the stories of the horseshoe crabs and the dragonflies, the story of the Great Dying so long ago.

Something so simple as the gas brewed from baking soda and vinegar can silently kill something as complex as a mammal. Next time I snuff a flame with CO₂, I will share the story of Lake Nyos, of the Great Dying--these are the stories that define us, stories that may someday save us.

Our stories make us worth saving.

Candle image by Matthew Bowden, who freely share. Thanks!
Lake Nyos photo by Jack Lockwood, USGS, in public domain (via Wikipedia)