At the top of Sunset Reservoir near Ortega and 28th, there are a series of park benches. If you sit there on a clear brisk winter day, you will see the Farallon Islands right on the horizon. They are seemingly within reach, yet farther than you think. They are about 27 miles away. If you could ride your bike across the water, it would take about 2.5 hours to get there.

Distances can be deceptive though. What if we explored the same span vertically instead of horizontally? Suppose for a moment that you went 27 miles straight up. The air pressure there would be less than 0.1 millibars. The air pressure that you experience sitting on the bench is about 1013 millibars, so at 27 miles the pressure is 10,000 times less. You’d be at the edge of space, unprotected, bombarded with energetic cosmic rays. If the sun is beating on you, the temperature could be 250F. At night, the temperature would be -450F. Space is harsh. I think of space like a microwave oven, full of radiation coming at you from every direction.

Now suppose you went 27 miles straight down into the earth. You would find yourself in the molten upper mantle, with temperatures around 2400F. Why is the earth so hot? More radiation, this time coming from the decay of uranium, thorium, and potassium. It’s a furnace powered by the ancient fuel of the universe.

In our daily lives, we don’t really think three-dimensionally like this. We are insulated from the harshness above and the heat below by a thin layer of atmosphere and a thin crust of rock. We are the bologna in whitebread sandwich, protected from earth’s forge and the infinite soup of space. We think and feel and move two-dimensionally, not comprehending how close we are to fire and infinity. What an amazing place this earth is.

How often do we pause to appreciate this fragile, miraculous balance that allows us to exist? Next time you visit Sunset Reservoir to soak up the sun’s rays, don’t just see the islands. Use your imagination and look up, and then look down.