In 1703, the world’s most esteemed scientific journal published a surprising letter from an anonymous correspondent. (At the time, until well into the twentieth century, anonymity often meant the scientist writing was a woman, though the word “scientist” itself was more than a century away, to be coined for a woman.)

The letter reported an astonishing discovery in the roots of pond plants placed under a microscope, still a relative novelty: Adhering to the delicate aquatic stalks were “many pretty branches, compos’d of regular oblongs and exact figures… the longest side not exceeding 1/2 of a hair’s breadth” — mysterious beauties smaller than any life-form anyone had seen, and yet appearing to be more than inert matter. “They may be rather Plants than Salts,” the shy scientist speculated shyly, but concluded that “they being so very minute that no judgment can be made of them but by the Eye,” it is impossible to “determine any thing positively.”

These beguiling marvels — tiny stars and fans and ribbons organized along exquisite radial and lateral symmetries — confused Darwin when he encountered them a century and a half later in the dust of the Cape Verde Islands and in the face paint of the native inhabitants Tierra del Fuego. All he managed was to gasp that “few objects are more beautiful,” seemingly “created that they might be examined and admired under the high powers of the microscope.”

Today, we know that diatoms — thousands of species of unicellular algae, each a living Noether theorem housed in a shell of opal — are not created for admiration but create the admirer: Every life-form on Earth depends on them. Tiny powerhouses of photosynthesis populating every body of water, these phytoplankton generate close to half of our planet’s oxygen, pillar its biomass, and absorb the atmospheric carbon dioxide that dissolves in the ocean.

To know of this extraordinary power makes the delicate beauty of diatoms all the more beguiling — nowhere more so than in Diatom Atlas by the German naturalist and clergyman Adolf Schmidt (1812–1899), who spent the better part of his life sampling cells from all over the world — Japan to Chile, Java to Barbados — to compose his pioneering portrait these miniature masterpieces of evolution.

Originally published in 1874 in black and white, the atlas was later reproduced on blue paper — a medium that originated in ancient China, then made its via the Middle East and Spain to Renaissance Italy to be used as a base for drawing and prints, giving two-dimensional artwork a hauntingly beautiful three-dimensional quality.

“I died for beauty,” Keats wrote with the requisite melodrama of the Romantics. Diatoms are a dazzling defiance of this aesthetic nihilism, urging us to remember that we are here to live with beauty. They could have remained mere producers of chemical energy no handsomer than a factory, and yet here they are, living jewels of the blue world. Pulsating beneath their shimmering shells and mathematically perfect symmetries is the elemental question: Why did the world have to be beautiful? And beneath that still, the eternal answer: No why; just is.