A DISSERTATION ON THE FIRST TREE.
ARCHEOPTERIIS A TREE, THAT CHANGED THE WORLD SO MUCH IT LED TO ITS OWN EXTINCTION
The first fossil I ever found was that of a fern. I am not sure what species. I remember it so well. I was on a field trip in Pennsylvania and there at the foot of a road cut among a lot of other rocks I picked up a cobble of red shale. I hit it with the chisel edge of my geologist’s hammer and the rock split apart neatly, along a bedding plane or weakness in the rock. There, exposed for the first time in perhaps hundreds of millions of years was the gray, iridescent imprint in a thin carbon film of a fern—a fossil. It was dark gray—all that was left of the fern was the carbon that made up its atoms— but the carbon “print” was arrayed just as it had been perhaps 300 million years earlier. And every little detail was visible, even the tiny hairs on the stem and leaflets.
Archeopteris is an extinct genus of primitive tree known only by its fossil remains. It’s leaves were fern like similar to the fossil fern I found so many years ago. This fossil tree -which looks like a Christmas tree—has characteristics of both ferns and conifers. It lived late in the Devonian period some 380 to 320 million years ago (mya).
It’s arrival on the scene was a watershed event that forever changed the entire Earth...its atmosphere, is rocky skin, and the life-forms which lived on its surface. Then, It quickly became extinct. It changed the Earth environment so extensively that it “found itself” no longer well adapted to the new ecosystem it created. It was source of its own extinction
In the Cambrian , Ordovician, and Silurian of the earth’s near 600 million year history of life, most of the attention of scientists was focused on the fascinating evolution of the invertebrates, brachiopods, corals and reef organisms, while in the Devonian much interest was focused the bizarre fish which appear in the world’s oceans at that time.. During most of the Devonian period there was not much happening on land.
At that time our present continents were not what they look like today, or were even where they are today. North America was much smaller than at present and far south of where it is located today. During the Devonian, what would become North America was much closer to the equator. Thus the Devonian climate was much warmer and drier too than it is now. (Recall that continents drift around on the Earth’s surface to collide together to produce mountain chains then break apart again in @ 500 million year cycles).
What is now our present east coast, was then dominated by high coastal mountains. The deep Atlantic did not exist off our east coast shore, there a shallow sea separated early North America from a line of offshore volcanic islands ( similar to modern day Japan and the Philippine Islands). Farther away, to the southeast was another large continental mass called Gondwana. Gondwana was moving slowly toward North America with which it would collide to form new mountain chains at the suture line, at the end of the Paleozoic, as it formed a super continent called Pangaea.
The floating continents or land masses themselves were rugged, rocky highlands, with very little or no vegetation. These bare rocky lands were exposed to driving rain, which unhindered by vegetation or water absorbing humus and soil, scoured out deep gullies and drainage channels. The tropical rains must have produced mud flows and earth slides which would have roared down mountains and accumulated in lowlands as muddy barren outwash or fluvial deposits. The earth’s surface was also exposed to a relentless intense sun. Exposure to heat and cold, to air and water physically and chemically decompose rocks into clays, oxides and other chemical products which lay on the surface subject to transport down slope by the first heavy rains . These critical mineral elements necessary for plant nutrition were washed downhill into rivers and into the oceans by surface water. The early and middle Devonian landscape was a hellish place with little greenery, no bugs, no bees, no animals—no shade, and no forests.
The land of North America during the early part of the Devonian did have some land plants—these were rock encrusting green algae, lichens, ,and liverworts, while club mosses and horsetails were low growing vascular plants that did not have true leaves and reproduced by spores. Ferns occur as well, but plants did not grow more than a meter high. The Devonian ferns grew as they do today in moist places close to water sources. The highlands, away from permanent water were barren and without significant vegetation. There were no flowering plants or seed bearing plants.
Early in the Devonian, atmospheric oxygen levels were much lowe as a a result of no forests with their layered concentration of green leaves to effectively produce oxygen by photosynthesis from carbon dioxide and water, Oxygen perhaps comprised only 17% of the atmosphere (present day oxygen is now at 21%) Carbon dioxide levels were correspondingly higher too...about 0.3% or @ ten times higher that what we have at present ( present CO2 comprises about 0.03%).
But all this was to change rapidly as the end of the Devonian Period approached, for a new plant was to evolve that changed the entire Earth, its atmosphere, its oceans and almost all living things as well. This new species -a tree—created new environments, new ecosystems into which new organisms would eventually adapt. Thus it helped diversify all the life on earth, even though it lived only a brief time, in geologic terms, from 380 mya to 320 mya then became extinct.
The history of how Archaeopteris was discovered is interesting and informative as well. The first paleontologist to describe Archeopteris was John Dawson (1871) who recognized it as an ancient fern and coined the genus name “archeopteris” which is from the Greek, and means: “ancient fern” (αρχαιος = ancient , πτερις = fern). For to the early paleontologists the leaves looked just like that of a modern fern—but one that lived nearly 400 million years ago (380 mya).
Dawson’s genus name “Archeopteris” made sense at first—it seemed to be a fern. About forty years later a Russian paleontologist, Mikhail Zelessky (1911) examining the stumps of fossil petrified trees in a the Ukraine described what he considered a new kind of ancient tree i that he found in Devonian strata. He considered it unusual since the wood tissues showed characteristics of the wood of conifer trees such as spruce and pine. He called this “new species” Callixylon (also of Greek origin. It means: “good wood”). He did make note of the fact that this new genus of plant was often associated with the “fern” Archeopteris.
But it was another fifty years later (1960) that Charles Beck also studying Devonian plant fossils came across specimens of Callixylon which had small side branches with the fronds and leaves of Archeopteris attached to it. It was clear that Archeopteris and Callixylon were parts of the same plant. [So perhaps had Dawson seen these samples, he may have named the genus “archeodendron” or “ancient tree” instead. But that is how science proceeds- only in fits and starts.]
But what was so unusual about this new plant fossil was that it had characteristics of both ferns and conifer trees. It had fern-like leaves and branches which carried “sporangia” which the sites where spores were produced just like ferns. Archeopteris, unlike ferns, had spores of of two types: a male and female form, perhaps a precursor to the conifers which produce pollen and cones. Also this tree had a tree trunk with vascular tissues or wood just like those of the evergreen or gymnoperms (the cone bearing trees —the conifers, ginkos, and cycads—) of today.
This now extinct tree Archeopteris looked like a top-heavy “Christmas tree”, but it’s branches were fern like as were its leaves. It had a “real” woody tree trunk. The bole of some petrified specimens had grown to three to five feet in diameter and to a height of thirty meters (near 100 feet). It was the first true tree*. It’s wood in cross section displayed tree rings, showing spring and summer growth patterns, similar to those of a pine or spruce. It had two different sized spores a male and female division not found in ferns.. Archeopteris with its characteristics of of both ferns and woody trees grew in wet places close to rivers and streams. But could also grow elsewhere. It had an extensive root system which went deep into the earth. In some Devonian sites these fossil roots are still visible.
From about 380 mya when the tree first appears it dominates the land area and out-competed every other species to very quickly becomes the dominant tree all over the Earth. Its wide and very rapid dispersal and dominance indicates that its ability to grow tall, rising well above the lower plants to form a true forest canopy gave it a tremendous advantage over those plants which had no woody support tissues or the ability to carry water upward thirty to one hundred feet to its leaves. But that is where the unrestricted sunlight was available, and by being able to move its leaves well above all other plants at the time it had a great advantage.
Wherever trees can exist today the Archeopteris probably lived there. It’s fossils are found on every continent where the Devonian and early Carboniferous strata occur, even on Antarctica.
It almost immediately became the dominant land tree almost all over the world and perhaps because of its widespread distribution, had a greater role than most any other in transforming the environment of the entire Earth.
It’s tall trees grew close together to form the first forests. The forest itself is a new ecosystem in which new plants and animals were to become adapted. Its great volume and display green leaves took in carbon dioxide and produced oxygen, raising the concentration of that gas and likely making the atmosphere more amenable to land animals and to other plants as well.
Soon after its world wide spread as dominant forest tree, we find the appearance of the first land animals. These were land arthropods, millipedes, centipede and spiders. Then too the first tetrapods appear late in the Devonian (four legged creatures) which evolved from relatives of the bony fish such as the coelacanth and lung fishes which evolved more rigid pectoral and pelvic fins making it possible for them and those who evolved later to literally haul themselves out of the water onto nearly dry land.
The branches and leaves of Archeopteris may have fallen seasonally as debris which accumulated on the forest floor then washed into streams, and there created a new nutrient rich environment where other organisms would evolve. The new nutrient rich stream and river waters were to attract marine bony fish into the fresh water environment, and encourage the tetrapods into these new ecosystems as well..
The canopy produced by the Archeopteris generated shade that altered the environment on the ground, making it more amenable to the emerging tetrapods and land animals and the first insects who were protected from dehydration and intense solar radiation in the shade of the forest.
The seasonal fall of fronds and leaves formed the first layers of forest litter and humus from which true soils would develop. Decay organisms (bacteria, fungi and eventually worms) evolved among the millipedes and centipedes in this new environment at the base of the trees.
After the advent of Archeopteris dominated forests and the soil they created, rainwater no longer just washed down slopes carrying loose rock and the valuable chemical products of weathered rock, (with its clay and essential minerals) because the Archeopteris’ decaying humus held these critical elements in suspension or by adsorption and absorption in the now newly forming soil so that it and other plants could utilize them more effectively. The humus also held water like a sponge, resulting in this moisture becoming available to other plants and animals within the soil.
This first ancient tree had a well developed root system which had an enormous impact on development of soil systems, on slowing erosion, on stabilizing slopes and on creating new ecosystems for other organisms to evolve. ( At the Gilboa Pertified Forest, near the Gilboa Dam in Schoharie County, New York there are many tree stumps, fossil leaves and fossilized root systems of these first trees exposed for view.)
At the end of the Devonian, when Archeopteris forests were widely dispersed this species may have even had a role in the great late Devonian extinctions. Some claim its rapid world growth into forming continental wide forests had the effect of reducing carbon dioxide levels in the atmosphere, causing a global cooling effect. The fall of global temperatures may have been one (of many) causes resulting in widespread late Devonian marine extinctions.
[ Extinctions are not all negative events, they have their positive effects too. Though in extinctions many organisms may die off, the survivors, often better adapted to the new conditions, are able to evolve and take over a food source, unoccupied niche or escape from predation and then—/proliferate. So we might add this result to Archeopteris’ other positive effects.].
Others cite extensive volcanism for the Devonian marine extinctions. Such an event could have caused atmospheric darkening and oceanic cooling. Many black shales are deposited in this period indicating a lack of oxygen in the ocean water. Some suggest the extinctions were the result of an asteroid impact. Many species of marine invertebrates become extinct during this time. Trilobites, brachiopods, and reef building organisms were particularly hard hit. Paleontologists claim that some 50% of all marine genera died out. But there were few impacts to terrestrial organisms. Archeopteris lived on into the Carboniferous so was unaffected.
The Archeopteris lived from about 380 to 323 mya and then for some reason, it rapidly became extinct. But while it lived, its leaves and fronds are so common in late Devonian early Carboniferous strata all around the world that it became an excellent marker fossil or index fossil, used to indicates that the rocks in which it was found are synchronous or of the same age as the Devonian and Early. Carboniferous strata. Good index fossils are those that were widely distributed and lived only for short time before extinction. Come to think of it humans might be —except for being extinct— perfect potential example.
Perhaps as the result of circumstances it helped to create, more atmospheric oxygen, less carbon dioxide, true soils, enriched soil nutrients, more stable slopes, etc., etc. it was no longer as well adapted to. In this new ecosystem. Other species that evolved within the forests it created were better adapted and were able to out-compete Archaeopteris.
Thus the story of Archeopteris may be a cautionary tale for humans. Archeopteris changed the Earth in innumerable ways and then quickly became extinct. It was so dominant and so effective in changing the Earth and its environment—it created an Earth so altered that it “found itself” no longer well adapted to the new world it had created, and died out. Archeopteris was the source of its own extinction!!
So perhaps we as humans should take note of the history of Archeopteris and beware of the prospect of our own extinction. Because we too, as a super dominant species have created a new world, vastly different in atmosphere, temperature, climate, fauna and flora from that which we emerged as a species and came into prominence about two million years ago. (This denouement of our own species came after a major extinctions too—that of the Pleistocene megafauna!!) Have we too changed our environment so drastically and radically that —like Archeopteris—we are too are no longer “adapted” and are slated for extinction?
Perhaps it’s still not too late. It is time for us to return the Earth closer to conditions that we as a species evolved into and adapted to.
We might begin this task by reforesting all the areas that we have foolishly deforested over our history—so as to return the CO2 levels back down to lower levels.
Let’s all plant a tree. Perhaps we can still save our species and a planet too.
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