There is one simple and powerful idea that strikes me as both deep and beautiful in its own right and as the mother of a suite of further elegant theories and explanations. The idea is that of "deep time": that the Earth is extremely old and the life of our species on it has been very short. When that idea first emerged it stood against everything that was then believed and it was to eventually change people's view of themselves as much as the earlier discovery that the Earth revolved around the Sun.
We know when the idea of deep time was borne, or at least first vindicated, for a University of Edinburgh professor named John Playfair recorded his reaction in 1788. "The mind seemed to grow giddy", he wrote, "by looking so far into the abyss of time." He had travelled to the Scottish coast with his geologist friend James Hutton, who later put his ideas together in a book called the Theory of the Earth. Hutton was showing him a set of distinct patterns in the rocks that could be most simply explained by assuming that the present land has been laid down in the sea, then lifted, distorted, eroded and once again covered by new sediments at the bottom of a sea. The Earth was not six thousand years old as then accepted calculations from the Bible decreed; nor had the strata of land precipitated out a vast flood as prevailing scientific views, informed by the best chemistry of the time, said.
It was an enormous shift to see the world as Hutton did. Appreciating the vastness of space is easy. When we look up at the stars the immensity of the universe is both obvious and awe inspiring. The immensity of time does not lie within human experience. Nature, observed on a human scale, passes only through the repeated cycle of the seasons, interrupted by occasional catastrophic earthquakes, volcanic eruptions and floods. It is for that reason that creationist and catastrophic theories of the Earth's origins appeared more plausible than those that were slow and gradual. But Hutton had faith in what he saw in the rocks, exhorting others to "open the book of Nature and read in her records".
His thinking about time created fertile ground for other grand theories. With huge spans of time available, then imperceptibly slow processes could shape the natural world. After Hutton came modern geology, then the theory of evolution to explain how new species slowly arose, and eventually a theory of the gradual movement of the continents themselves. All are grounded in deep time.
Hutton's views were a huge challenge to religious orthodoxy too, for when he wrote at the close of his book, "we find no vestige of a beginning--no prospect of an end", he challenged both the idea of a creation and of a judgement day.
The beauty of his idea remains. If we look into the abyss of time, we may not grow giddy, but we can simultaneously feel our own insignificance in the Earth's 4.6 billion year history and the significance of the precise moment in this vast span of time in which we live.