This got me to thinking about a couple of famous comments:
"This is a little tiny blue skin that is 50 miles wide."
-- William Shatner
Look again at that dot. That's here. That's home. That's us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives.
-- Carl Sagan
I can't begin to compare with the poetic and profound words of either man, but I had a thought looking at today's APOD and considering both quotes. In a way, Shatner is noting an added emphasis on Sagan, in terms of how tiny our realm of existence, of all life is on Earth.
From a distance, the globe of Earth looks small (cf. Sagan), but even that gives us too much credit (cf. Shatner). Our biosphere is more 2-dimensional than 3-dimensional. We're just in a verry narrow band on the surface of the globe. All of life exists between about 4.2 miles up and about 7 miles down from the sea-level point. (The tardigrade can live in extreme conditions, for example, still, not much of anything living has been found anywhere above about 22,000 feet. We found life at the Challenger Deep at the bottom of the Mariana Trench in the ocean. We've even found life quite a ways under the surface of the earth, both under the dry ground and under the ocean floor, but so far, nothing below about 7 miles below sea level, that I'm aware of.)
99.999% of humans can be found in a shell that is only about 3.1 miles in thickness, between sea level and 16,700 or so feet.
And as long as we're putting a tight bound on it, the 99.999% of us are further reduced to the 30% of the surface of the Earth that is land. And you could even toss out part of that, because over half of it is "not very habitable" (deserts, mountains, arctic regions). A common estimate, I can't verify its accuracy, is: 24.6 million mi2
out of 57.5 million mi2
. So ...
We humans all live on a tiny, pale blue globe. A rocky planet that looks blue because it is 70% wet from a fairly thin layer of mostly-liquid water. And we only live on a sliver around its surface. And we only even live on about 15% of that surface, mainly. We're on the dry part, not the pretty blue part. We'd like you to come visit us, but only if you're nice.
-- Mark Goldfain