Trilobites could be said to be the first complex animals to evolve real eyes on our planet Earth.
Maybe.
We just don’t know.
Abruptly, in rocks that date back about 560,000,000 years, trilobite shells began to appear in ancient sea bottom muds and silts with no evidence as to how they had reached such an highly evolved state . By "highly evolved” I mean that trilobites appeared full-formed in the Cambrian fossil record wearing eyeglasses. Very cool eyeglasses too; wrap arounds, ghetto grannies, thick-lens nerdy types,...almost every species of trilobites had their own particular style of eyeglasses except the species of trilobites which were blind.

Calcite! The stuff of caves, great carved statues, ocean bottoms, the white chalk cliffs of Dover.
Calcite, a crystalized form of CaCO, calcium carbonate of which the more transparent form is Iceland Spar. The trilobites manufactured their light-collecting lenses from this inert compound to allow them to detect and react to the phenomena of light; a biological revolution.
In the book TRILOBITE: Eyewitness to Evolution Richard Fortey quotes Shakespeare’s The Tempest...

Full fathom five thy father lies;
Of his bones are coral made;
Those are pearls that were his eyes;
Nothing of him that doth fade,
But doth suffer a sea change
Into something rich and strange.


“If to voyage back to the time of the trilobite is a historical sea-change then there is nothing stranger than the calcareous eyes of the trilobite. And pearls are chemically the same as the trilobite unblinking lenses, being yet another manifestation of calcium carbonate, although peals are exquisite reflectors of light rather than transmitters of it. The weirdness of Shakespeare’s line results from his suggestions of pearly opacity, the hints of a corpse transformed; dead, yet seeing. The trilobite saw the submarine world with eyes tessellated into a mosaic of calcified lenses; unlike the dead seafarer, his stony eyes read the world through the medium of the living rock.”

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Pretty cool book.