Fusible Hydrogen

The secret to safe fusion power was discovered December 5th, 2022 in the world of Athena Minerva in a laboratory in a city called Livermore, California. It would be made affordable and common a decade later.
Much as the 20th century was associated with the invention of the airplane, the discovery of inexpensive petroleum, world wars, atomic fission and fusion bombs, humanity's near destruction of Earth's biosphere, and the discovery of the dark planet, Pluto, the 21st century brought about the end of physical military warfare, the discovery of inexpensive fusion and various other clean power sources, printed food, and the declassification of Pluto as merely one of many minor dwarf planetoids in the Kuiper Belt.
The metaphysics of the apparent influence of the mythological god of the underworld on the entire human race of planet Earth for almost exactly a century was fodder for philosophical debate, songs, and poems for centuries afterward, wherever there were historians.
But the harnessing of hydrogen (possibly one of the first atoms in the universe) as a power source was instrumental in humanity's gradual change of motivation from primarily fear of lack of access to limited resources to motivation primarily from joy and wonder, knowing that sufficient food and power was available to all who dared generate it for themselves, and knowledge waiting for anyone who dared investigate.
Not only was life on Earth greatly improved when the politics of fearmongering lost its teeth in the face of widespread luxury and leisure, but spaceflight was dramatically improved as well, (though not as much as later scientific discoveries, of course). Hydrogen being widely available throughout the galaxy, it could be collected during travels which would otherwise have been impossible or tremendously impractical.
If one considers water (from which hydrogen and oxygen can be repeatably extracted and recombined) to be an extension of hydrogen, then humanity's switch from water power to petroleum and Uranium power to hydrogen fusion power is metaphorically identical to a battle between Pluto and Neptune, lending many theologians and historians and philosophers to wonder if humanity was not repeating the same battles (between waste and sustainability) over and over again despite changes in scientific knowledge, religious beliefs, and personal philosophies.