One of the more interesting fossils you will ever find is a trilobite. This three-lobed ocean-going creature was an arthropod related to insects and crabs. Its closest living relative is probably the horseshoe crab, although behaviorally, it may have been more like a lobster or crayfish. Today we find beautifully preserved trilobite specimens in rocks dating back to the beginning of life on Earth. What can we learn from trilobite eyes?
We can study and learn from trilobite eyes because they were made of the mineral calcite. Calcite is the same mineral that makes up limestone, so it is quite hard and efficiently preserved. In its purest form, it is perfectly clear. Calcite possesses what scientists call a double index of refraction. Because of the arrangement of atoms in calcite, light arriving at one angle passes undisturbed while light at another angle will be split into two beams.
In addition to being made of calcite, the trilobite eye was made up of a honeycomb of hexagons. There could be several thousand hexagons in the eye arranged so that light from any angle would be refracted into the animal’s eye. If it came perpendicularly, the light would go straight to the back of the eye. If it came at an angle, the double index of refraction would still bring the light to the back of the eye. There was a small wall between the hexagons so that light from the hexagons did not overlap each other. When arthropods grow, they molt their outside layer, and the new larger layer hardens. The eye material would add hexagons as the animal got larger.
This kind of eye is similar to the eye of a housefly. Like flies, trilobites would have been especially good at detecting motion. They also would not have a problem with near-sightedness or far-sightedness. Something an inch away or a mile away would both be in focus at the same time.
There is one vision problem the trilobite would have. It’s called spherical aberration. The thickness of the materials in each hexagonal lens would not be the same, and that difference could distort the image. In the trilobite eye, this problem was solved by magnesium atoms added to the calcite in a way that corrects the aberration. Modern opticians do this with what they call a doublet lens.
Scientists have observed other special features in various species of trilobites. They have found some eyeless trilobites that probably lived in areas with no light, such as very deep in the ocean. Other eyes were mounted in ball-like structures that could move. Still others were positioned so that the animals could bury themselves in the sand like a stingray while their eyes could still look out for food or enemies.
There are many lessons we can learn from trilobite eyes. The incredible complexity is a tribute to God’s wisdom and design. In this case, the complexity is of particular interest because trilobites were some of the first animals to live on this planet. That fact presents a problem for those who say complexity is a result of evolutionary forces over a very long time. Trilobites already had a sophisticated visual system when they first appeared in the fossil record in the Cambrian period 500 million years ago. Darwinistic models cannot explain the trilobite eye, but the God of the Bible can.
— John N. Clayton © 2019