What’s interesting, amongst various other fruits, about life here on Earth are human energy sources. Humans require regular animal metabolic energies but they also add two other energy needs: brains and their manifestations. That means folks have a higher need to fuel their big brain relative to other critters; but also an ever greater need to energize their engineered creations. This latter is by far the most energetic endeavor a species has ever journeyed.
So, what is the source most relevant to human energy needs? It’s all linked to one fundamental thing: gravity.
First, the sun shines energy due to the nuclear forces that are stronger and nearly beyond gravity. However, gravity is the reason these nuclear forces are enacted. The sun’s massive gravity crushes elements together so hard the nuclear forces must act with an energizing transition to larger elements. This means gravity leads to sunshine.
Second, this sunshine hits plants and builds moderate warmth for biochemical reactions. The plants and temperature lead to other life forms via being a food link as well as an oxygen link in stable conditions where the solvent of water can easily maintain homeostasis of cellular life.
Third, the water cycle. As noted above water is the solvent of Earth’s life. The water cycle is fueled by the sun but defined by the Earth’s atmosphere and lithosphere. We know about the sun and gravity but here the planet’s gravity is important even though subtle. Earth’s gravity holds down a thin gas layer, tight but not that tight since it’s gas and flies about easily. Within the complexity of the gravity driven water cycle is its ability to deposit water uphill. In the end that means gravity gives you hydroelectric power. Possibly ironic as well, since water goes uphill because of gravity.
Fourth follows closely with the atmosphere’s motion, which is gravitationally motivated by the sun’s energy and the rotation of the Earth. The gravitational nature of the Earth’s rotation is confounding but correlated. That is beyond this discussion. What’s important is that if Earth were tidally locked to the Sun and had only a bright and dark side, it’s winds would be intense due to the uneven heating (heat distribution via convection). Yes, wind power is ultimately granted by gravity.
Fifth, geothermal and petroleum; a metamorphic gold mine for energy. It’s because Earth’s gravity also holds down an all encompassing rock layer, which is a smear of molecules that tend to crystallize but are at high pressures made molten; this molten and crystal layer are dependent on the pressure gravity creates. Caught in all this deep time and deep pressure is organic matter from trees to animals. You guessed it, gravity made crude oil and coal. And hopefully we’ll master using geysers or volcanoes to run electric generators.
Sixth, wood burning for cooking, heating, steam power, go figure. You should think photosynthesis, but we also need to account for Earth’s gravity as well as the Sunshine. The Earth’s gravity holds down water and the tree itself. Wood’s density and composition are thus a good fuel due to the gravitational impetus of the planet it grows out from.
In all, you can likely link most energy sources we have here to humanly manipulate as somehow made possible by gravity as an energetic force. What it is, we don’t and likely can’t know. What it does we do know to be energetic.
The Broad Spectrum Life 