Earth records provide us with this information: Ice cores, tree rings, ocean sediments, stalactites and stalagmites in caves, growth rings in corals, tusks, and mollusks. These archives accrete memories on time periods varying from months to millions of years, allowing us to see a spectrum of Earth changes on various temporal and spatial scales—how biology, ocean, and ice respond to climate change in signature patterns, and the points at which those systems are pushed past thresholds.
In geology, an “unconformity” represents an aberration in the normal accumulation of sediment, a glitch in the record-keeping of Earth’s history. “A stratum of amnesia in the geological record, where overlying rock, significantly younger than what lies below, represents some break in an otherwise continuous story of formation,” is how writer and poet Kim Stafford defined it.2
The longest lacuna in Earth’s history is known as the Great Unconformity. It represents a temporal gap ranging from a hundred million years to over a billion years, depending on the location. It’s visible in the Grand Canyon as the boundary between the Precambrian Vishnu Schist and the Cambrian Tapeats Sandstone, between which there is a billion years of missing time between about 1,600 and 600 million years ago. Looking at this line in the strata, it is hard to fathom all that would have conspired across that vast gulf of time, for which there is simply nothing. If it were instead to have been the last billion years that was erased, it would obliterate the entire history of complex life. No trace of a single animal having ever walked the land. No dinosaurs, no whales, no humans, no pyramids.
How does a billion years go missing? The Great Unconformity has long been a geological mystery, in no small part because it is a challenge to reconstruct history when records of history are missing.
It turns out, ice sheets are good shredders. Recent research suggests that the Great Unconformity may be a result of Snowball Earth—when the planet descended into deep cold (about 700 million years ago), and glaciers covered most of the land. A billion years of history was ground down by ice and bulldozed into the seafloor, where it was subducted into the Earth’s mantle and recycled into magma, ready to be remade into new history—albeit with a few hidden remnants of the past stored safely away in subterranean crystals.
While the erosive action of ice sheets may have been responsible for the largest unconformity in the Earth’s lithosphere, ice sheets themselves are some of the best memory banks on our planet. Greenland stores over 100,000 years of history. Antarctica stores over a million. These ice sheets are written by the daily weather, each snowstorm condensed into the jagged rhythms of ice age cycles that steadily build into mile-high mountains—the great brains of our planet, perched on the poles. (...)
Antarctica has been the slowest beast to awaken, but the icy tentacles that reach out to moor the giant are starting to slip. These floating ice shelves extend out from where the ice sheet is grounded to the bedrock, helping to stabilize the interior, but now they are starting to weaken from the forces of ocean warming and rising seas. As the ice shelves disintegrate into the ocean, the ice upstream accelerates its descent, increasing sea level.
In 2022, double heat waves hit the Arctic and Antarctic, temperatures soaring close to 40 degrees Celsius higher than usual. The Conger ice shelf in East Antarctica said its final farewell following this heat wave. West Antarctica has long been considered the more vulnerable to near-term ice shelf loss, but now, even the East is starting to show its fray. Heat makes easy work of forgetting. (...)
Before a tipping point in a complex system, there are early warning signals that may be detected. The most widely applicable of these early warning signals is “critical slowing down”—the phenomenon we are all familiar with before our computer crashes, and rather than heed the implications of this slower processing power, we jam at the keys in frustration, doubling down on our demands until the computer blacks out. These are the times information is most likely to be lost if it hasn’t been secured in long-term storage.
Critical slowing down indicates the system is losing its ability to attain its previous equilibrium and is instead becoming attracted or pulled into an alternate state. It is a loss of resilience, a loss of the negative feedbacks that help keep a system rooted in stability. Various subsystems that are sensitive to thresholds—such as the Amazon rainforest—are already showing signs of critical slowing down.
Given the complexity of the Earth System, it is hard to fathom the extent of information loss currently underway. There are, however, attempts to quantify the memory loss in the Earth System.
In one model, where anthropogenic CO2 emissions are the stressor, and the strain on the system is the ability of the land and ocean to sequester carbon, researchers show the latter is inherently slower than the former. They estimate that 60 percent of Earth’s memory had already been degraded by 1959, and that the ability for Earth to build-up memory has been impaired, reducing its capacity to respond to stresses within its natural stress-strain regime.16 Estimates of persistence in this model—akin to critical slowing down—are increasing, signaling a departure from the bounds of Earth’s natural regime well before 2050, if the stressors of rising atmospheric carbon dioxide continue their current trajectory. The ocean is undergoing memory loss too, increasing variability and reducing predictability of future temperature patterns.
The intractable problem we face is the asymmetry of timescales: It takes time to build memory, but it can be erased in a geological instant. Like so many things we take for granted, it is difficult to see these stabilizing forces until they are gone. As we untether the anchors of the past, the future becomes unmoored.
The intractable problem we face is the asymmetry of timescales: It takes time to build memory, but it can be erased in a geological instant. Like so many things we take for granted, it is difficult to see these stabilizing forces until they are gone. As we untether the anchors of the past, the future becomes unmoored.
by Summer Praetorius, Nautilus | Read more:
Image: Katherine Streeter
