We’ve known for a long time that while the Sun creates tides, it’s the Moon that calls the shots .
Its existence was a very considerable push in the conquest of the land.
The evolution of life on our planet is an extraordinarily complex natural phenomenon, not a scientific trial of controlled variables. For that reason we cannot reproduce the process at will. Life is something much more sophisticated than a laboratory experiment.
This implies that we will never be able to know precisely what would have happened if our planet did not have something as special as a giant satellite. What we can do is reflect on the probable implications that the Moon had on one of the most transcendental moments of evolution: the conquest of the terrestrial environment.
Leaving the water is like changing the planet
Our organism, like that of any other species, eats, breathes, excretes, defecates and moves in an automated way because it is in its territory , that is, it lives in an environment to which it is naturally adapted. Biological species have evolved in this way, by screening and discarding any evolutionary novelty (mutation) that reduces our level of adaptation to the environment and positively selecting only those that increase it or, at least, do not interfere.
But if they take us out of our ecological niche and alter the rules of the game, everything changes. When we watch movies that take place in space, we get the slightest idea of the number of problems that engineers have to solve to keep us alive outside the home . If we want to survive, we are forced to carry a ship and a space suit, that is, with a substitute for our ecological environment on our backs.
For aquatic animals, getting out of the water would be a challenge comparable to moving to Saturn for Homo sapiens . They would have to have a terrestrial suit that would protect them from drying out, from the brutal thermal variation between day and night or from the crushing of their organs due to gravity (on land they do not have the thrust they have in water).
Surprisingly, this titanic feat took place on our planet naturally, several times and with different protagonists (arthropods, molluscs, annelids and vertebrates, among others). Of course, with an exceptional ally: the tides.
The conquerors of the terrestrial environment
The absolute anatomical, morphological and physiological revolution that the conquest of the terrestrial environment entailed was not, as you can imagine, an easy or quick process. In fact, some 25 million years (Ma) elapsed from the late Devonian tetrapodomorph fish – the elpistostegalids – to the truly terrestrial forms of Lower Carboniferous vertebrates .
Nor was there any directionality or desire to conquer in this process. The protagonists of this evolutionary leap simply adapted to the new circumstances as a result of the purest Darwinian struggle for survival on the shores of the oceans.
Let’s put ourselves in situation and move to about 400 Ma back. Twice a day thousands of marine organisms suffered the torment of being swept by the tides into hostile territory. Most of them succumbed when they got stranded in intertidal zones while waiting for the saving new rise of the tide. But the luckiest, the weirdos with mutations that made them more resistant to the infernos of intertidal sludge, survived and continued to exist.
The pressure of intra- and interspecific competition maintained over time favored forms capable of withstanding terrestrial inclemencies for increasingly longer periods until species emerged that could survive indefinitely on land.
First they were plants –some 425 Ma ago– which, thanks to their photosynthetic capacity, did not need organic material, absent in a land completely devoid of life.
Some time later, these pioneer plants provided survival to gastropods (snails) and arthropods (spiders, myriapods and insects), creating the first more or less stable terrestrial ecosystems. Thus it was possible that about 365-360 Ma ago the first four-legged vertebrates could lie in the sun on the humid swampy plains of the Upper Devonian.
The particular importance of the Moon in the tides
We’ve known for a long time that while the Sun creates tides, it’s the Moon that calls the shots . The enormous magnitude of the terrestrial satellite, together with its proximity, mean that the gravitational force exerted on the waters is double that attributable exclusively to the Sun.
Its existence was a very considerable push in the conquest of the land. This evolutionary acceleration was also favored by the fact that in the Devonian the Moon was closer to the Earth and the tides were substantially more intense.
In fact, researcher Hannah Byrne and her collaborators say that the Moon’s great mass and location provide ideal circumstances for creating wide tidal ranges and the consequent isolation of pools. Speaking in silver, the Moon promoted the creation of survival shelters in the form of lifesaving pools. This, in turn, could have led to suitable pressure to favor the selection of novelties such as limbs or internal respiratory structures in stranded animals. His novel calculations and algorithms suggest that tidal variations of more than four meters would be optimal to favor these processes. This is precisely how they existed in the area of the southern block of China, where a large number of fossils of terrestrial vertebrate pioneers have been found.
From there, a new chapter was inaugurated in the history of vertebrates that made possible the appearance, among many other species, of ours.
We could conclude, seen what has been seen, that Homo sapiens are indebted to the Moon. She is not only beautiful. Not only does it light up our nights with a trickster romanticism. We not only have to thank him for being an inexhaustible source of inspiration, poetry, dreams and crushes. Quite possibly, humanity owes its very existence to the beautiful satellite.
A. Victoria de Andrés Fernández , Full Professor in the Department of Animal Biology, University of Malaga