The Riddle of the Cambrian Explosion

Many at least once heard the term "Cambrian Explosion" and vaguely know that this is the most ancient period in the history of the Earth, when suddenly life appeared on the planet. How did everything happen in reality?

©Depositphotos
In fact, little is known about the Cambrian period today, because the events that we will speak about took place 542 million years ago. About earlier times (Archean and Proterozoic eons) science and at all - until recently, almost nothing was known. This is understandable, because the Precambrian strata, in fact, seem almost dead, they almost did not discern traces of any life. But the Cambrian explosion is precisely characterized by the sharp emergence of diverse forms of life, which appeared as if from nothing. Darwin at one time called this period a fact that does not fit into his theory of gradual evolutionary changes.

Darwin did not know then that during the Cambrian explosion, many forms of living organisms simply began to acquire a sharp mineralized skeleton. However, life in the Precambrian (cryptozoic) was still, therefore it is called the period of "hidden life". Today, science knows that many of the groups of animals found in the Cambrian strata lived in cryptozoic. Simply most of them were soft creatures that did not have a solid shell or skeleton. But the mystery of the Cambrian explosion still remains, just now the conversation is not about the fact that complex forms of life emerged from nowhere, but why so many of them suddenly acquired a mineral skeleton. This could be due to changes in environmental conditions. For example, this effect could be caused by a sharp decrease in the acidity of water, as a result of which calcium carbonate, the most common skeleton-forming material in animals, has become less soluble in sea water and easier to precipitate, but there are many other hypotheses.

Hallucigenia lived on the ocean floor 505 million years ago, during the Cambrian explosion / ©Depositphotos

In order for animals to have carbonate skeletons, it is not enough only that the environment becomes favorable. It is necessary to have special genes and enzymes, through which living organisms would be able to control the formation and growth of calcium carbonate crystals in certain parts of their body and in the required quantity. A very important role in the formation of such skeletons has enzymes of carbonic anhydrase, they accelerate the reaction of converting dissolved in water carbon dioxide into bicarbonate about a million times. Carboangainases are generally very common in the animal kingdom. In addition to the fact that they contribute to the formation of the skeleton, they perform many other functions. Until recently, it was not known when exactly and in what order living organisms acquired carbonic anhydrases. However, not so long ago, Australian and German experts studied skeletal-forming enzymes from a primitive archaic sponge, a living fossil that has lived on our planet for more than 200 million years - Astrosclera willeyana. Based on this study, scientists were able to determine that all the numerous and diverse carboanhydrases of animals originate from a single protein that had the last common ancestor of all animals.

Astrosclera willeyana / ©Depositphotos

"The last common ancestor of all animals," no doubt, lived long before the Cambrian skeletal revolution. It turns out that the animals were initially well prepared (preadapted) to the development of the mineral skeleton - they from the very beginning had enzymes that can dramatically accelerate the formation of calcium carbonate. Probably such enzymes, Precambrian animals with a soft body, were used not for the formation of a skeleton, but for other purposes (that carbonic anhydrases perform in the body and other functions mentioned above). When the environment began to favor bio mineralization, different animals independently of each other gained from this benefit for themselves, forming with the help of these enzymes their skeletons and shells.