I think that part of what is surprising is that our brains cannot comprehend the scale of earth so we see the photo as a model of earth and wonder how it's poss

I think that part of what is surprising is that our brains cannot comprehend the scale of earth so we see the photo as a model of earth and wonder how it's possible that so little water can spread throughout. At model scale, the water wouldn't spread all the way around the globe because of viscosity and surface tension.