The primary producers of the food web are plants. Algae, ferns, etc... All require energy from the sun. Now up the next level is plant eaters and omnivores. Next up the ladder are the carnivores and omnivores. The energy transfer. Works from the sun, to the plants, to the animals to the other animals, to finally decomposes.
It's hard to tell. I was looking at a diagram representing the atmosphere. 50 miles is right on the edge of the Mesosphere. The temperature is about - 135 or so. It does climb up to about - 49 according to the Royal BC Museum.
