What if it rained for a million years?
What the Earth has done before, what it might do in the future, and why this matters — by Nigel Clark & Bronislaw Szerszynski
It rains a lot in Northwest England where our university is based. Prevailing westerly winds blow in from the Atlantic. Like the currents that bring warm water from the tropics, these winds are ultimately driven by the ‘surplus’ of solar energy which falls on the tropical latitudes relative to the cooler temperate and polar zones. Plumped with moisture evaporating from the Gulf Stream, air flows rise as they meet the British Isles, dumping much of their water load on the western side of the islands.
The daily, often hourly, ebb and flow of rain gives us something to talk about. But sometimes small talk grows into weightier conversations. Or even falls into silence. In early December 2015, an extratropical cyclone rolled in from the North Atlantic. Storm Desmond, as it came be to be known, broke 24-hour rainfall records in parts of Cumbria, Lancashire and the Scottish borders.
When the overflowing River Lune submerged an electrical substation on the night of 5th December, over 60,000 houses in and around our university hometown of Lancaster lost power for several days. Cut off by the closure of the local bus station, train lines and several bridges, the partially flooded city ground to a halt. Without a power source, many of our students found themselves totally disconnected from phone conversation and online social interaction for the first time.
what if started raining and didn’t properly let up for a million years?
A couple of days of heavy rain can make a big difference. But what if started raining and didn’t properly let up for a million years? It’s not an unthinkable prospect. Gathering geological evidence points to a phase of exceptionally rainy and humid weather some 234 million years ago: what science writer Peter Brannen refers to as an ‘obscure spasm of extreme climate change tucked into the middle of the Triassic period’.
Previously considered localized and relatively insignificant, the hydro-meteorological outburst that scientists have labelled the Carnian Pluvial Episode now looks to be ‘geosynchronous’ — its effects showing up as an incongruously clay-rich layer at the same time in the geological record right across the planet.
At this stage in the Earth’s history the planet’s landmasses had drifted together to form the supercontinent Pangaea, a vast expanse of land with a near-endlessly stretching arid interior. Then came the rain — mega-monsoonal conditions that look to have lasted over a million years. Over this time, driving rain and flowing water ground mountain chains into sand and gravel. Excessive turbidity and ocean acidification killed off coral reefs and with them hosts of marine organisms, while sweeping extinction carried off many terrestrial animals.
Though not as severe as the monstrous extinction events that opened and closed the 50 million-year Triassic period, biotic turnover in the Carnian Pluvial event left its mark in the course of evolution. But what is devastation for some orders of life can be an opportunity for others. The clade of Dinosauria — a previously rather inconspicuous subset of backboned animals restricted to southern Pangaea — flourished in the wet, humid conditions. As the Triassic world recovered, dinosaurs nudged out crocodile-like competitors, greatly expanding their range and diversifying into new niches.
Why should an ‘obscure spasm’ of rainy weather sandwiched into a long-gone geological epoch matter to us? Like every twist and turn in the Earth’s history, the shifting evolutionary trajectories in which the Carnian Pluvial Episode is implicated played their part in forging the world, the ecologies, the bodies that ‘we’ eventually inherited. Replay the story of the Earth with even a minor variation, as evolutionary biologist Steven Jay Gould liked to say, and it would be extremely unlikely to lead to Homo sapiens.
the Carnian Pluvial Episode is beginning to look like a possible analogue for the Earth’s near-future weather
There are more immediate reasons why a million-year rainy spell ought to concern us. A current hypothesis proposes that the Carnian Pluvial event was triggered by an exceptionally large release of carbon dioxide from seabed volcanoes, resulting in rapid global warming. Oxygen isotopes extracted from fossil marine organisms suggest that level of warming which caused the acceleration of the hydrological cycle was about 4 -7°C. That figure is significant, for it is very close to estimates of global climate change in our own time if current trends of greenhouse gas emission continue. With climatologists predicting an intensification of the global water cycle by around 24% by the end of this century, the Carnian Pluvial Episode is beginning to look like a possible analogue for the Earth’s near-future weather.
We are not going to weigh in about the likelihood of this happening, though we do feel deeply grateful to the researchers and writers who have prised the Carnian Pluvial Episode out of its former obscurity and ushered it into the not-so-small talk of contemporary climate debates. We are social scientists, not natural scientists, so strictly speaking what our planet got up to hundreds of millions of years before the emergence of humans is far from our domain. So why does it matter to us, and why do we think it should matter to everybody, that our planet can turn on a million-year downpour?
Finding out that mega-monsoons are part of Planet Earth’s repertoire, as we’ve noted, sounds an alarm about what could conceivably happen again. But it does more than this. The Carnian Pluvial deluge — inscribed in the distinctive band of clay it laid down and the evolutionary pathways it opened up — provides evidence that the Earth can change. And change quickly. It offers us one striking example of more general capacity of our home planet to leap or lurch from one mode of operation to another.
At critical junctures, our planet has reorganized its component parts
When a deep cut through rock reveals visible distinct layers — think of the Grand Canyon, or any motorway bisecting hill-country — what we see are the material traces left by a planet that has been behaving differently at various moments in its past. As geologists like to point out, the Earth is especially dynamic and changeable. This is why, compared with the other planetary bodies in our solar system, Earth ‘is a treasury of strata’, as paleontologist Jan Zalasiewicz puts it — its rocky crust revealing a richness and diversity of layers without equal in this corner of the cosmos.
This doesn’t mean that anything goes. Rather, new kinds of planetary behaviour become possible at particular times, by way of specific events. At certain critical junctures in the Earth’s history, scientists tell us, our planet has reorganized its component parts, in the process acquiring the capacity to do things that it couldn’t do before. The rise of biological life and the biogeochemical cycles that life set in motion is one of these significant moments of reorganization. The emergence of organisms capable of turning sunlight, water and carbon-dioxide into storable chemical energy — the process of photosynthesis — is a further great reorganizing leap.
We shouldn’t assume, however, that the Earth’s acquiring of new capabilities has always hinged upon life. The formation of the dense metallic centre of our planet — an iron-rich liquid outer core revolving around a solid inner core that generates a powerful electromagnetic field — is another momentous planetary achievement. So too is the congealing of the Earth’s crust, which forms a kind of lid beneath which the dissipating energy from the planet’s core gradually assembled itself into the vast, churning convection currents of the mantle layer.
a reminder that when Earth systems reorganize themselves, the ultimate outcome is deeply, fundamentally unknowable
Most of the truly ‘great’ transformations that earth and life scientists speak of lie deep in our planet’s past. But that doesn’t mean they are over. And it doesn’t rule out forms of planetary reorganization that might be relatively insignificant or ‘obscure’ by planetary standards yet would be devastating for organisms such as ourselves and for all the complex arrangements we depend upon.
It’s unlikely that greenhouse gas emissions generated by certain sectors of the human population would simply reprise Carnian Pluvial conditions. The planet has changed over the intervening two hundred and thirty plus million years: the forms and distribution of life, the positioning of continents, the orbit and tilt of the Earth are not the same. What a glimpse of the mid-Triassic mega-monsoonal episode might best do for us, then, is to serve as a reminder that when Earth systems reorganize themselves, the ultimate outcome is deeply, fundamentally unknowable.
The obvious lesson is about minimizing those anthropogenic pressures for change that risk nudging planetary systems into new and strange configurations. In other words, leaving fossils fuels in their subterranean strata, slowing the extraction of mineral phosphates from their rock formations, protecting large-scale ecosystems. Such is the alarm sounded by climate science and by the more encompassing fields of Earth system science and Anthropocene studies.
which of the Earth’s own variabilities and pressures for change might we want to join forces with?
But there are other ways of thinking about — or through — processes of planetary reorganization. As well as addressing the changes we don’t want to risk triggering, we could also consider what manner or degree or scale of planetary reorganization we do want to contribute to. To put it another way, which of the Earth’s own variabilities and pressures for change might we want to join forces with?
For thousands, in some cases hundreds of thousands of years, human agents have been applying fire to their surroundings, selecting and transporting life-forms, altering the flow of water. On a planet that is inherently changeable, at times alarmingly volatile, non-intervention is not always the best option. Or an option at all.
It’s about leaving enough of the Earth’s own dynamism and forcefulness intact
Then again, it’s not all about us. In the really big picture that Anthropocene thinking brings into relief, it’s more than a matter of protecting the Earth as it currently stands, more than just a question of erecting boundaries around those aspects of our planet’s current operating state that we’ve come to rely upon. It’s about leaving enough of the Earth’s own dynamism and forcefulness intact so that it maintains the potential to do its own self-organizing.
For better or worse, it’s this propensity of our home planet to take us by surprise that has made us who and what we are.
More to the point, it’s the Earth’s capacity to take itself by surprise that has made this planet what it is today. Or rather, that’s what our planet is — in its very being: this tendency, from time to time, to leave itself behind and turn into something unprecedented and inconceivable. And that’s a planetary parade that we don’t want to rain on.
