Here’s something I’d never heard of: The Great Unconformity. The Grand Canyon is like a timeline of earth’s history, with each layer going back farther in time as you descend its walls, all the way back to rock that formed 1.8 billion years ago at the bottom.
The only problem is that a billion years worth of rock is missing. The timeline jumps from the Tonto group of 700 million years ago to the Vishnu basement layer 1.6 billion years ago. Geologist John Wesley Powell was first to discover this way back in 1869, but still no one really knows what happened to all that rock.
There are several competing theories, apparently, and they all likely played some role. For example, rock layers were weathered away by ice during the snowball earth period.
Geologists at the University of Colorado, though, published work this week providing thermochronological evidence for what seems to be the primary cause.
During the breakup of the first Pangea supercontinent, the western end of the Grand Canyon region was lifted so high that the basement layer came to the surface, but it was still miles underground at the eastern end.
The whole North American plate seems to have tipped like a saucer as Rodina split apart, and millions of years of rock slid into the sea.
exposed at the surface
the great divorce
The Atlantic Meridional Overturning Circulation is the conveyor belt that transports warm water from the tropics northward and cold water south, balancing the heat distribution in the Northern Hemisphere and allowing for the relatively mild temperatures in Europe. New evidence has emerged this week from the Potsdam Institute providing further evidence that the AMOC is undergoing a loss of dynamic stability and may be on the verge of collapse.
The culprit is climate change, as lighter freshwater from melting land glaciers accumulates on the surface of the ocean, reducing the sinking action that drives this circulatory current.
The new report made headlines, but few seem to be providing the details about what this could mean for our future. The triggers of abrupt climate change in the paleo record remain a mystery, but the leading hypothesis is that these Dansgaard-Oeschger oscillations are related to changes in the AMOC. What seems to happen is that this fresh meltwater from a warm period sitting on the surfaces of the northern oceans causes this current to stall, which make temperatures in the Arctic plummet. Because freshwater freezes at higher temperatures than saltwater, this surface layer leads to an increase in sea ice, increasing the polar albedo, making the temperatures in the Arctic even colder, creating a feedback loop with cooling progressing southward toward the equator.
Another factor at play is the Beaufort Gyre, a clockwise-swirling current in the Arctic Ocean that traps cold freshwater. Historically, the gyre has reversed every 5-8 years or so, releasing that cold down into the North Atlantic, but the reversal is now a full 8 years overdue, and it’s holding more freshwater than all of the Great Lakes. When the reversal finally comes, it will release even more cold freshwater into the North Atlantic, sending Europe into a freeze and adding to the problem of the stalling AMOC. The effect is large enough that researchers have called the Beaufort Gyre a “ticking time bomb“—one that’s still ticking 4 years later.
The most extreme example of what an AMOC collapse can do may be the Younger Dryas, where temperatures rapidly fell 10 °C in Greenland and 5 °C Great Britain. With human-released CO2 tipping the scales in the opposite direction, no one really knows what’s going to happen. But it’s long been my opinion that it was this sudden climactic shift that drove the mammoths and mastodons to extinction, along with 70% of the rest of North American megafauna, and not human predation. The situation reminds me of this 19th century drawing of all the mammoth tusks from Siberia sitting on the trading docks in London. To me, it looks like Hokusai’s The Great Wave.
a frozen ocean
This week, researchers at Yale monitored retinal waves in the brains of mice to show that they were dreaming visually before birth, practicing the use of sight so they would be prepared for possible predators the moment they open their eyes.
Newborn humans exhibit some of the same behaviors, so this is believed to imply that fetuses dream as well. What’s interesting, though, is the question of what the dreams would be. Some kind of ancestral, epigenetic memory of sight?
an infant dreams
in the womb
Honestly, I can’t quite wrap my head around this week’s sciku article. The role of dopamine in our external rewards system has been studied extensively, but we also have regular passive spikes of the neurotransmitter cycling trough our brains spontaneously—in mice it’s a spike every minute or so—and we don’t really understand why.
In a study published this week in Current Biology, researchers demonstrated that mice are not only responding to these regular spikes, but are able to alter them. The suggestion is that it might play a role in the foraging process, with a tiny dopamine hit every minute reminding them to stay alert for some greater reward. The chemical process seems to prod us forward, making sure we’re never quite satisfied. I wonder if it might play a role in ADHD?
At least that was my interpretation. The press release doesn’t quite make sense to me, and the study itself was even more impenetrably written. But I think that’s what it means? Maybe I just need a nap.
under my hammock
Who knew that the moon’s orbit wobbled on an 18.6-year cycle? Well, actually, we’ve known about this since 1728—and Bronze Age peoples knew about it thousands of years ago, and tracked it in their megalithic monuments all over the world.
But a paper in Nature Climate Change this week studied the impact it will have on high tide flooding in the coming decades. Right now we’re approaching the major standstill, where tides variation is the lowest, hiding the impacts of sea level rise on coastal flooding. In 2034, we’ll be at the minor standstill, which exacerbate the flooding.
he tells it again
walking home from the bar—