Dating back some 386 million years, it’s the world’s oldest-known fossil evidence of a forest, predating by two or three million the site in Gilboa that was previously regarded as the earliest of its kind. Shown above, left: Aerial shot of a well-preserved Archaeopteris root system. (William Stein & Christopher Berry)
No matter how much of the Appalachian Trail you’ve hiked or how many Catskill or Adirondack High Peaks you’ve bagged, our Eastern mountains look measly when you hold them up against the Alaska Range, the Rockies, the Cascades, the Sierra Nevada. There is, however, a different way to look at this comparison that might make you feel better: through a lens of time rather than altitude. The still-seismologically-active mountains of the West are much younger than the long-eroded Appalachians. The orogeny (mountain-building period) of the Rockies only dates back 55 to 80 million years. Compared to the East, that’s chicken feed.
While the oldest mountains on Planet Earth are in South Africa, the Blue Ridge in Virginia makes the Top Ten list, with rock layers datable back 1.2 billion years. The uplift of the Appalachian chain began in earnest about 470 million years ago, during the Ordovician Period, when the East Coast of the North American paleocontinent Laurentia lay about where the Hudson Valley is now (although the entire continent was then positioned slightly south of the Equator). A crescent of small islands that geologists call the Taconic Arc was riding a tectonic plate that bumped into Laurentia, creating the Taconic Mountains and adding what is now western New England to the Iapetus Ocean coastline. Today’s Taconics are but a tiny, worn-down remnant of what was once a major geographic feature.
A second arc of islands, Avalonia, followed with greater force after linking up with the small continent of Baltica (which was later to head off eastward again, to become the basis of Western Europe). It struck Laurentia about 430 million years ago (Silurian Period), gradually closing up the Iapetus Ocean, adding the rocky mass of eastern New England and triggering the Acadian Orogeny, which piled up what would become the northern Appalachians. A massive range called the Acadian Mountains then paralleled the coast from New York to Virginia.
The most violent wave of orogenic activity in the East was yet to come, when Gondwanaland slammed into Euramerica (Laurentia + Baltica) to form the temporary supercontinent Pangaea. This was the Alleghenian Orogeny, which spanned three geological periods – Mississippian, Pennsylvanian, Permian – from 325 million to 260 million years ago. It created the Alleghany Plateau and pushed the Appalachian mountain mass – then the Central Pangaean Mountains – to heights that likely exceeded the present-day Rockies.
That upheaval wasn’t what made our Catskills happen, however. Their genesis came earlier, in the masses of sediment washed westward in a great delta of the Iapetus – by then a narrow inland sea – as the Acadian Mountains eroded. This occurred during the Devonian and early Mississippian Periods, 395 to 325 million years ago. Technically speaking, the Catskills aren’t even classified as mountains, but as a “dissected plateau,” formed not by uplift but by eons of erosion from water running downhill to the receding sea.
Don’t be disappointed, though. If you were one of those kids who wanted to be a paleontologist when you grew up, you may recall that the Mississippian and Pennsylvanian taken together add up to what’s called the Carboniferous Period. Yes, that’s when all those coal deposits in Pennsylvania were being formed – from huge masses of plant life. The shoals of sediment worn down from the Acadian Mountains became fertile soil for some of the world’s earliest forests. So densely did they grow that they ended up causing catastrophic climate change that is the opposite of the situation facing us now, sucking CO2 out of the atmosphere and fixing it underground as peat and coal. Air temperatures and humidity dropped; habitat became fragmented; many species of plants and insects went extinct in a global event known as the Carboniferous Rainforest Collapse, about 305 million years ago.
And now, a new scientific discovery in the northern Catskills gives us something amazingly special about our region to inspire pride of place: In the December 2019 issue of Current Biology, William Stein, professor emeritus of Biological Sciences at Binghamton University, published a study with dramatic photographs of the spreading imprints of Devonian Period tree roots from the floor of an abandoned quarry in the Green County town of Cairo. Dating back some 386 million years, it’s the world’s oldest-known fossil evidence of a forest, predating by two or three million the site in Gilboa, on the western edge of the Catskills, that was previously regarded as the earliest of its kind.
What makes the Cairo site even more exciting to scientists, according to Stein, is the diversity of tree species found. The Gilboa site was dominated by specimens from the genus Eospermatopteris: primitive, short-lived, weedy, shallow-rooted plants resembling tree ferns. Cairo has them too. But the knockout discovery at the quarry – painstakingly excavated from layers of sandstone, and now protected from being obliterated by off-road vehicles by strategically placed small boulders – is a labyrinthine network of roots spanning 18 feet in diameter and digging deep into the soil. Stein has identified it as an Archaeopteris, a very early tree with a woody trunk and broad, flat leaves adapted for efficient photosynthesis, believed to be a precursor of seed-producing trees. He described the root system to Smithsonian Magazine as “strikingly modern, essentially what you’d see outside in my yard right now.”
Remnants of a third type of early tree were also found at the site, tentatively identified as an isoetalean lycopsid with stigmarian rootlets. Such plants were common denizens of coal swamps of the Carboniferous Period, but according to the researchers, they were not previously known to have existed as early as the mid-Devonian.
Stein and his team hypothesize that the stand of trees at the Cairo quarry was killed by a flash flood. Skeletal fossils of primitive types of fish also were found nearby. Millipedelike creatures called myriapods likely shared this forest ecosystem, but dinosaurs would not begin to evolve for another 140 million years. And the uplift of the present Rocky Mountains was still more than 300 million years in the future. So take that, Wild West.
