Fire in the lake - Above, a lake of fire, the fire of volcanic activity. It has often seemed strange to me that we are burning "fossil fuels" (incompletely combusted light-energized carbon compounds) when we are essentially on an 8000-mile diameter ball of hot rock which has a thin shell. Fracking, which involves horizontal drilling at depths in the shell, begs the question of why we are not directing more intelligence to using the heat beneath our feet. Geothermal.
Layers of the Earth (YouTube video - 2:45)
"...and let's discuss: the inner core, outer core, mantle and crust..."
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To figure out the size of the molten rock ball we are on, it took a pillar, a well, an 800 kilometer hike, and a Summer solstice day. "Sticks at different angles to the sun's rays will cast shadows of different length." Cosmos - Eratosthenes calculates Earth's circumference (YouTube video - 6:34)
Carl Sagan tells the tale of how Alexandria's chief librarian, upon reading about the Sun lighting up the bottom of a well in a town much further south on the Summer solstice day - something that did not occur in Alexandria on the same day - devised a way to measure the earth's circumference, 2200 years ago. *****