Geology Rocks II: Can you isolate a single day in a million-year-old chunk of ice?
This makes me want a blue freezie
Welcome to a special mid-week edition of The Amateurist! Part one of this question happened a few days ago, just in case you missed it.
Just for fun, I wanted to see if I could work this question from the perspective of ice. Glaciers, permafrost, and super pressurized blue ice all hold onto atmospheric information in a similar way to how stratified rock does. The major difference is that most ice just doesn’t have much longevity on this planet. Especially not on the scale of eons, periods, or epochs. Regular (in geologic time) warming periods have ensured that no ice has been found that’s older than 2.7 million years. That being said, scientists think there’s a chance that there’s 5 million-year-old ice waiting to be discovered in Antarctica.
However (and it’s a big however), what can be found in these ancient ice samples is significant to mapping climatological change since the last glacial period.
When snow falls, the crystallizing water traps air molecules and floating particles in the flakes. They all fall together and pile up when they reach the ground. Air fills the space between the snowflakes while they are close to the surface. The more snow falls, the heavier the layers are on top and the more the snow gets compressed into denser and denser layers the further down they become. The air is then trapped within the layer of snow as tiny air pockets that preserve the atmosphere’s composition at the time the snow fell.
In any given ice core sample, an annual snowfall is only about a few millimetres thick. Depending on the colour and other characteristics of the snow and the trapped air, the layers are pretty easy to see and count season over season.
Regular ice is subject to melt patterns and glacial interference, though, so it’s not as reliable a source for older samples. The deeper the packed snow gets, the more it’s compressed and the harder it is to use dating methods on the air inside. Eventually geothermal heat melts the oldest ice and sends it back into the wild as water. Not helpful.
Enter: blue ice.
Unlike typical ice, blue ice isn’t layered based on age. It’s formed in more exposed areas where the densest and oldest layers drive up to the surface. These regions don’t experience any net additions or losses of snow - blue ice is usually a result of high winds and little to no melting over literal ages. Blue ice, in all its dense and colourful glory, is true to its name.
To answer the question here, it’s probably a no for getting a glimpse into a full million-year-old day. The way the ice needs to be compressed to become blue ice (gigatons of pressure) means that there’s little chance that anything could survive intact other than microscopic air bubbles. Not bones, not plants, not anything. And even those air bubbles are few and far between. Ice just moves in more destructive ways than the regions of land that yield paleontological data.
Even if a unique event could be established (aha, a bit of soot!), getting a precise measurement for time is much tougher than dating things on land. Ice can’t be dated, but the air inside can. The tough part is actually doing it.
Princeton geochemist Michael Bender was the first to use the potassium-argon dating process on the air contained in blue ice. It was definitely a way to date the samples without having layers to count, but the method is more designed for longer timelines. The closest it can get is what the climate was doing within about 100,000 years of the sample.
That’s a great window when you’re looking at tens of millions of years, but not if you’re trying to pin events down to centuries or decades. There is a chance that cross-referencing other data could lead to the kind of specific data we’re after. Where this dating method fails, there’s so much information out there for mapping geological time, like fossils and radiometric dating.
So I guess it’s possible, but only if there’s something to compare the data to that’s less ambiguous. Ash in the ice? Ash in a layer of rock? Line them up and test them out. You never know!
Verdict: most likely not. Open to being proven wrong by a real science person.