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Many evolutionary biologists use the word ‘terrestrialisation’, as if to describe many plants and creatures came out of the seas to arrive on ‘land’ . Yet how could there be terrestrialisation when there was no ‘terre’ there?
Evolutionary biologists recognise that it is a big jump to be able to adapt to dry conditions from having lived in water. But the image persists of evolution having occurred by this movement of plants and animals from water to land. We hear time again how creatures and organisms ‘conquered land’. But how? There is no discussion about what that land look like. In many cases that land was rock. Nothing would have lasted long on that. Let alone ‘conquered' it.
The great evolutionary leap
The great evolutionary leap
Plants and creatures getting from water to land is seen as one of the major advances of life, and we certainly would not be here if this had not occurred. But most views seem to think that the animals and plants just hopped, dropped, crawled or wormed their way from water to land. There is virtually no mention of soil on the way.
It is one of the greatest parts in the story of evolution. We would not have much of an earth without it. But that great evolutionary leap could not have been made without soil. Yet it is rarely mentioned. Plants and creatures could just move from water to land - they needed soil. In future, we need to imagine a layer - albeit thin - between air, water and land, that provides the dynamic between them. That is soil. And it has not always been like it is today. We shall work out what it may have looked like throught the ages.
"Schematic overview of the terrestrialization process and the different stages/Natura 2000 habitat
types in order of hydrosere succession from open water towards (semi-)terrestrial peatland" (Mettrop 2015
This is a useful diagram showing the various routes to land, and shows how different adaptations would be made at different sites. But it doesn't explain the evolution of these adaptations which would have taken a lot longer than a few years .
Conquest
Conquest
Time and again you can find terrestrialisation as being a 'conquest'.
Classically "Life originated in water. Then there was terrestrialization, the conquest of dry land" Terrestrialization: The Conquest of Dry Land by Plants (Ulrich Lüttge)
Even recently
How plants conquered land (Rensing 2020)
How plants conquered land: evolution of terrestrial adaptation (Kumar 2023
Image from Plant Evolution: Landmarks on the path to terrestrial life Look no soil!
Crawl
Crawl
In most biological textbooks, you can find sentences that portray the major evolution of plants and animals from water on to land, without soil. Many seem to think that there was some sort of invasion by various marine bosies just crawling - or working - their way out of the water on to tland.
“First animals to colonize and exploit terrestrial and freshwater ecosystems”
“Centipedes are some of the very first creatures to crawl from the sea onto the land were probably very similar in appearance to modern centipedes”
“The ancient creatures who first crawled onto land may have been lured by the informational benefit that comes from seeing through air”
“Prehistoric fish crawled out of the water and began the evolutionary lineage we sit atop today.
“Invertebrate arthropods, including insects, millipedes, scorpions, and spiders, were on the move, gradually making their way on land.
“The protection of ozone layer caused life to move out of the water and onto land. Plant life and death was important in creating organic deposits”
“The fossil record of euthycarcinoids in the Cambrian, including trackways made on tidal flats, clarifies the marine-to-terrestrial transition in the myriapod lineage.
“Then something extraordinary happened. The very first vertebrates began dragging themselves on land.
“The remarkable evolutionary journey of life on our planet, from its early origins to the moment our ancestors began walking on earth
“This was a very tall order. To make the jump from swimming around in the ocean to walking around on land appeared to be virtually impossible. So how did they pull it off?”
“The emergence of plants and animals from the sea on to land, this being one of the major advances in the history of life on Earth.”
“This interval encapsulates the time of increasing terrestriality.”
“An event of great importance was the movement of life (as land vegetation) to land in the Devonian time.’
“Eventually, animals crawled onto dry land”
Some creatures may have crawled on to land, especially the later ones, when there was something for them to crawl on to. But not in the early days. Most would not last long on dry land. They would have crawled straight back. It would have been a hot and hostile world with no cover. Think of those iguanas on Galapagos rocks. They go back to the sea to feed.
Mike Benton sees things differently.
“At the time when the land, seriously began to green, we think of that perhaps as life crawling out of the ocean - plants and animals. And once they're on land, they're everywhere. The key point is they're not because moving out of the water like this was quite a dangerous thing to do. The initial plants kept their feet in water.".
As soon as we recognise this point, we are hit with a massive question. If the plants have to have their feet in water – and notice he does not use the word roots – how did they move from the sea to land? If that land is just rock – how do they green the planet?
If the plants were to put down roots, they had to have something to put them down into. And that must be either cracks in rocks, silts or soils. How did those rocks become soils – and did those tippy toes help break up the rocks to help make soils? Soil is much more reliable at providing water for the plants than rocks – where the water runs off.
The book ‘Terrestrial Invasion’ by Colin Little (1990) is perhaps the fullest articulation of the terrestrialisation. The author takes takes an ecophysiological approach: ‘The theme of this book is the invasion of land by animal lines which originated in aquatic environments. He devotes chapters to 1) whether several animal groups moved directly from sea to land or whether they invaded fresh water first. Possible routes included 1) via mudflats and sands 3) via dense vegetation near sea or 4) rocky and shingle shores and 5) an indirect route through estuaries. He spells out the major shifts in physiology needed for many body functions - like excretion and sex - to change from water to air,, but doesnt explain how they can occur.
Then there is the matter of how the most important group of animals – insects – took over the airwaves above earth. He believes that insects probably evolved from myriapods – many legged creatures - saying ‘the lines that probably invaded land are probably myriapods and not insects, which evolved once they were semi-terrestrial. He goes on: “terrestrial leaf litter and soil habitats grade into interstitial habitats of seas and fresh waters, as emphasized by Ghilarov (1959) providing a route for invasion for invasion by ancestral forms”.
The structures to survive in air are very different to those needed to survive in water. Water exerts pressures not felt in air. But air does not provide a regular moist environment – needed for many functions – both in animals and plants. Think about sex. In water the eggs can float about with the off chance of being fertilised. Out of water there has to be internal insemination. Creatures cannot just let the eggs drift in water, till they were inseminated. Yet evolution is gradual development of random advances. So how does a male organ and female organ fitted for each other develop overnight?
Ghilarov
Ghilarov
The painter Bosch knew the move to land was a more tricky issue. In his famous painting ‘Garden of delights’ he depicts that “creatures came from aquatic forms – through some sort of ‘amphibiotic state’" Ghilarov 'Introduction' 1970. That 'state' is depicted as the curious pink device coming out of the water in the left hand panel of the triptych. Of course, creatures did not evolve through this device.
The Russian scientist Ghilarov spells out the challenge "The concept of the origin of terrestrial arthropods from aquatic ancestors is generally accepted; However, the specific paths of evolution of individual groups of opinion are very contradictory. Suffice it to recall that, for example, insects have according to different researchers for the last 40 years, been bred directly from trilobites (Handlirsch, 1925; Heegard, 1945), crustaceans (Crampton, 1928), from Symphyla (Tiegs a. Manton, 1947) and other centipedes ( de Beer, 1930), and Onychophora (cf. Du Porte, 1965)! He explains chapter by chapter how all the body systems - the protective, respiratory, excretary and reproductive - all need to change - together. They can only do so slowly - in a protected environment, which must be the soil. Without the soil, insects could not have evolved.
To understand the evolution of a group, you need to see real ways of its development, under those environmental conditions, in which the evolution of this group of themes could take place, and not in any other way. The conditions of existence in water and on land are so different that a direct transition from life in water to life in an open atmosphere is impossible for most groups of animals."
The triptych is called “Garden of earthly joys" in Bosch's home Prado Museum.”
Air
Soil
Water
Summary of M.S. Ghilarov’s theory on the origins of insects, which we shall explore, explains the emergence of wingless (Apterygota) and winged insects (Pterygota).
Here he also shows how worms (Annelida) , Myriapods (millipedes /centipedes/ symphyla) and Oniscoid (woodlice) may have emerged.
'The Invasion of land in deep time'
'The Invasion of land in deep time'
"The invasion of the land was a complex, protracted process, punctuated by mass extinctions, that involved multiple routes from marine environments. We integrate paleobiology, ichnology, sedimentology, and geomorphology to reconstruct Paleozoic terrestrialization ....Late Paleozoic soils (300mya - first mention of soils) commonly contain pervasive root and millipede traces. Lacustrine animal communities diversified, accompanied by increased food-web complexity and improved food delivery which may have favored permanent colonization of offshore and deep-water lake environments. These trends continued in the Permian". (Buatois et 2022)
This scientific detective story to discover the answers to the question 'how did soil get here'?' has never been explored in such detail before. Bits and pieces, but nothing like an overall picture of what went on where or when. You may have read or heard about the story of life ON earth, but not IN earth. Soil is right under our feet, yet holds many secrets to be revealed. These secret stories reveal much about the rest of life ON earth as we cannot have life ON earth without life IN earth.
There was no terrestrialisation until about 100 mya, when there was some deep soil to help new inhabitants. For terrestriauliksation there had to be widespread 'terre' or earth for them to live in. The more demonstrable travels are less than 200mya in the Jurassic period, with perhaps the first true 'terrestrialiser' occurring during the Cretaceous period with the arrival of that ancient looking woodlice a mere 150-100mya.
What are the tools we can use to discover what went on?
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