Most people know the world visually. The eye is able to perceive electromagnetic radiation, one of the varieties of which is light, and transform it into a picture perceived by our brain.
If we look around, we will see that the eyes have both a tiny midge and a bird hovering in the sky, and at a fish floating in a sea abyss. All this suggests that living beings on Earth should have a common ancestor, in which the first appeared something similar to photosensitive cells, later evolved into the eyes. When did this happen?
Archaeologists, studying ancient fossils, have long noticed that in sediments you can draw a sharp boundary, located at the turn about 541 million years ago. And if up to this point the ancient deposits were extremely poor even with poorly preserved biological remains, then after this time limit biological diversity multiplies many times. It was then that the Earth was inhabited by animals that remotely resembled modern species. The skeleton appears in animals, a large number of organisms with mineralized tissues appear, the fossils of which reach our days practically in an ideal state. This most important event for the planet was called Cambrian Explosion.
The surviving fossils have survived so well that, using the latest technology, scientists can draw conclusions not only about the external structure of beings that lived 540 million years ago, but also about the inner structure and their sense organs. It is interesting that all the fossil organs of sight that they were able to detect have a rather complex structure. They could not come out of nothing without a long evolution. Probably the animals that first acquired eye analogs should be sought before the Cambrian Explosion – during the period called Ediacaria, which began about 635 million years ago.
Unfortunately, very few fossil remains of living creatures of the Ediacaria period were discovered. This can be explained by the fact that on the planet there were only soft-bodied organisms, so their bodies had no chance to reach us even in the form of fossils. We will venture to name the time when the animals had eyes, at 600-580 million years ago.
What did these first eyes look like on the planet? They were very different from the current ones. Most likely, it was just a cluster of photosensitive cells that could tell their wearer the intensity of the light to determine the time of day or to assess the local depth (all life in those days existed in the seas and oceans). Those first animals that received the rudiments of vision showed better fitness than other species, which resulted in their advantage, reproduction and rapid evolution of the organs of vision. Gradually the layer of photosensitive cells became thicker, could catch more light and even began to respond to movement, which helped animals find food.
|It’s interesting: some modern inhabitants of the sea depths have visual organs that can look like the very first ones eyes in animals. For example, a hydra that uses photoreceptors located on tentacles reacting to the shadows of passing animals or determining the approach of night.|
For a short evolutionary time, the organ of vision acquired a complex structure, which we see in representatives of the Cambrian fauna.