Trilobites are one of the most fascinating ancient arthropods, they appeared together with many other complex creatures during the Cambrian explosion some 500 million years ago.
They lived a highly adaptive life with their perfect forms and remained prolific in the Cambria seas for over 250 million years. They came in dazzling varieties and are the best-preserved members of the Paleozoic era. One particular feature of trilobites had a structure that expert optic physicians could not even think of having found in animals, their marvelous compound eyes. The eyes of trilobites are the earliest known visual system that existed with unbelievable complexity, perfection, and superiority, at a time when according to present-day biologists no complex life should have existed. The most important and distinguishing feature in trilobite eyes is calcite. Calcite is one of the commonest and most durable minerals on Earth. Buildings made of calcite-rich limestone thousands of years ago still stand strong and beautiful. The calcite found in the eyes of trilobites is transparent and has optical properties, if you fracture a piece of calcite it always breaks in line with its own atomic structure, in a rhombus shape that allows light to pass through it, the presence of this optical calcite in the eyes of trilobites makes them totally unique in the entire animal kingdom, as the eyes of nearly all animals are composed of soft organic material. And because their eyes were made of calcite like the rest of their body, they too have been very well preserved and reveal astonishing details about their perfect structure and function.
The compound eyes of Trilobites
Most trilobites had compound eyes of holochroal type with many thousands of closely packed hexagonal lenses covered under a single corneal layer. Each lens captured an image from a slightly different angle, forming a mosaic-like picture and giving the trilobite a wide range of vision to perceive danger from any direction The resolution and detail of the images also depended on the number of lenses they had. One species of trilobite had 3,000 lenses per eye, and another had 15,000. The complexity of their eyes and brains' ability to process images from thousands of lenses that early in life must have been incredibly great. according to scientists compound eyes of trilobites that lived 500 million years ago were as advanced in function as the eyes of dragonflies today.
The most interesting eyes in the world
One particular group of trilobites phacopina had an even more interesting visual system, the like of which never appeared again in any living being. These trilobites had compound eyes consisting of a few to a few hundred separated lenses that were larger and thicker, the shape of these lenses looked more like a marble. and if you gazed through a clear marble, you would see that it refracts light at different angles, resulting in a blurry image. this innate problem in thick lenses is known as spherical aberration. Since the lenses of phacopids were made of thick crystal, they too must have experienced the same problem. but in the 1970s When Mr. Kenneth Towe shone light through the lenses of a trilobite, instead of getting a blurry, ill-focused image, he obtained an extremely sharp image. it is as if the trilobite defied the physical laws, The mysterious reason behind this exceedingly sharp image, was only discovered many years later when paleontologist Euan Clarkson and physicist Ricardo Levi-Setti examined and found out that the lens in trilobite eyes had an extraordinary shape. The shape of these lenses matched the two ideal constructions worked out by the 17th-century optic pioneers Descartes and Huygens to counteract spherical aberration. They were totally unaware of the fact that the very designs they proposed were being used by trilobites 500 million years ago. There was another surprising fact that came to light: the lens in the eyes of trilobite was not based on a single unit, but a doublet This doublet nature of lenses is something only humans have invented, it is not ever observed in any living being. Because trilobites lived underwater and the refractive index of water is different from that of air, the second lens unit along with that ideal shape was absolutely necessary, without it the trilobite wouldn't have seen well underwater. the second lens unit with a lower refractive index based on chitin and intricately arranged magnesium atoms at the interface between the two lenses helped bring the light to focus at a single point and thus allowed the trilobite to receive an extremely sharp image of its surroundings. The trilobite with its extraordinary visual system shocked scientists so much so that they were perplexed to even consider it a reality.
The questions that arise
These shocking discoveries about trilobites' eyes gave rise to many questions, How did trilobite know the optical properties of calcite and use it for vision? How did it get the ideal lens shape that only expert opticians could draw? How did it know that a second lens with a lower refractive index would be needed underwater? Moreover, how did both lenses happen to align perfectly to meet the visual needs of trilobite?! Did Trilobite think of it all and develop these astonishing eyes by itself? The trilobite itself indeed had no knowledge or power to make any relevant changes in its body, nor can any of this ever be explained in terms of evolution because trilobites appeared suddenly in the fossil record and their complex eyes existed never before and never after them, The miraculous existence of trilobites, and the stunning and unmatchable structure of their eyes could only be the masterwork of a supreme creator who is all-knowing and all-powerful. He is the one who gave trilobites and all other living beings astonishing features compatible with their surroundings right from the moment, they first appeared on Earth.
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