An Even Thinner Line

A couple of weeks ago I wrote about a thin line, one hundred kilometres thick, that permits life on earth.  Last week, sitting on seat 13A inside an Air Canada Embraer 190 jet ten kilometres up, I thought about an even thinner line.

We were flying on a clear, blue-sky day.  At our cruising altitude I could see as far away as 360 kilometres.  A perfect day for flying.  From the ground the sky must have looked beautiful and appeared calm.  Much like I had thirty years prior, children might have been gazing up and seen the white condensation trail left behind by the metal bird I was in.  It all looked so effortless.

Inside the cabin the illusion of calm was shattered.  The fasten seat belt sign was on (they always are these days) and cabin service had been interrupted.  We were asked to remain seated.  The winds were strong.  I could feel the plane pitching, rolling and yawing.  It is this last movement, the yawing, that I have always found particularly unsettling when in a plane.  Flying sideways is not much fun.  Anyhow, during this harmless roller coaster ride I started thinking about an even thinner line that supports human life.  Just outside my window, centimetres away, was an environment that would kill me within minutes - if not seconds).

At 8.8 km in altitude Mount Everest is the highest point on Earth.  The lowest is the Challenger Deep in the Mariana Trench.  This point in the ocean is almost 11 km (10.9 km) deep.  So Earth's crust has a difference of 19.7 km between its highest and lowest points.

Without a form of submarine human's cannot survive under the water.  While certain military submarines can circle the globe without resurfacing they are limited by their need to be refueled and, if that problem is solved, the need for food on board.  So, below our feet, we are limited to living at a minimum of sea level (if you exclude the Dead Sea area and places like Death Valley).

Above our heads the story is a little more flexible.  While humans have ascended Everest without assistance it is generally agreed that human beings can not survive permanently much above 5.5 km in altitude (ref: Hypertextbook).

So our thin line of 100 km, while important to life on Earth, is really limited to 5.5 km for human beings.  Yet, when we look at planes in the sky or imagine mountain summits, we imagine their heights to be unreachable - to be much further than the corner store in your neighbourhood.

If you took the same distance and lay it on Earth's surface the realization that these distances are comprehensible and very understandable is made pretty clear.

5.5 km.....a short, thirty minute jog away.



Let me know what you think about what you have just read. Please and thanks!