That’s step four. It’s extra, but almost necessary everytime.”
(( since i have been sick for almost three months now (yes three months, you read that correctly), have “emils guide from hell: when you feel sick” as an excuse for not answering asks. pardon just the scenery change and also pardon my lEGS HAHAH A
i wanted it to look like i was wearing boxers or something and i have these shorts i wear under skirts– i dunno, iTS DUMB BUT I TRIED OKAY HERE TAKE THE DAMN GUIDE ))
Ice cores from Antarctica and Greenland have been invaluable in deciphering the history of Earth’s glaciers over the past 800,000 years. When snow is compacted into glacial ice, tiny bits of atmosphere are trapped in the open spaces, and the age of the ice can be found by literally counting the layers created by each year’s snowfall. By sampling cores of ancient ice, scientists have managed to sample the atmosphere as long as 800,000 years ago – the previous record for oldest atmosphere sample from an ice core.
That air gives us a record of CO2 changes in the atmosphere that correlate strongly with temperature changes and the waxing and waning of glaciers – CO2 goes down and the earth enters a 100,000 year ice age, CO2 goes back up and that ice age breaks up.
Prior to 800,000 years ago, we know there were glaciers advancing and retreating, but something different was happening. Instead of glaciers lasting 100,000 years, they lasted only 40,000 years before they collapsed. There are theories for why this happened, mostly focused on CO2 changes, but without a better sample of the atmosphere that’s a difficult hypothesis to support.
This photo shows a team of scientists from Princeton University and the University of Maine on the Antarctic Ice Cap in an area called the Allan Hills. See how the ice is blue? Blue color is a signature of very old ice, ice that has been at high enough pressure that most of the air bubbles have been squeezed out. The Allan Hills are an area where the ice sheet is ablating – older ice is coming up to the surface and melting or sublimating away. Therefore, cores into this ice have the potential to sample ice even older than what we’ve found through other drill cores.
There’s one problem though – when glacial ice is squeezed back up to the surface and ablated, it loses the “annual bands” that let scientists say exactly how old the ice is. The scientists in this study drilled shallow cores into this ice and got samples of the atmosphere, but how to figure out its age?
To do that, they used one thing in the atmosphere that does change gradually over time – the abundance of one isotope of Argon, Argon-40. Argon-40 is a gas that makes up about 1% of the atmosphere and it is produced by radioactive decay of an isotope of Potassium. Potassium is pretty abundant in the earth, so over geologic time the amount of Argon-40 is slowly ticking upwards. By measuring the abundance of Argon-40 in the atmosphere they got from this ice core, they estimated that the air they were sampling was trapped around 1 million years ago with a margin of error of ± 200,000 years. Not nearly as small of error as you get by counting individual bands in an ice core, but enough to say that this ice predates the start of our current cycle of 100,000-year glaciations.
The chemistry of the ice allowed the team to argue that they were able to sample across the boundary between a glacial/interglacial cycle; ice preserves an isotopic record of the temperature when it forms and they see a large shift in temperature during this section of core.
Those temperature shifts are correlated with changes in CO2, just as in the other ice cores, but the absolute numbers are different. The largest ice sheets in the last 800,000 years formed when CO2 levels dropped to about 180-190 ppm; nothing in this ice core got down to below 220 ppm. On top of that, the highest CO2 measured in this core from 1 million years ago was higher than any measured CO2 content between 800,000 and 450,000 years ago.
In other words, when the Earth switched from having ice sheets last 40,000 years to having ice sheets last 100,000 years, atmospheric CO2 was changing too. Once CO2 dropped a bit, ice sheets were able to expand more than they previously could – hinting that the causal link between CO2 drops and longer ice ages might be correct.
Those CO2 changes are small compared to the atmospheric change that has happened in the last century. The difference between 40,000 year and 100,000 year ice ages observed in this core is 30 ppm at the low end and 7 ppm at the high/interglacial end. In the last 200 years, burning of fossil fuels and land use changes have increased atmospheric CO2 to 400 ppm and this core again verifies that it has been well over a million years since Earth’s atmosphere has had this high of concentration of greenhouse gases.