The one in which I strongly advise you to buy stocks in Nivea
In a continuation of the existential crisis upon which I embarked last week, today I found out that “Ice Age” the movie is as old as my (much younger) classmates – that’s right Gen-Z’ers, I’m looking at you. However, what is perhaps even more surprising to me than the revelation of my advancing age, is the scientific/historical accuracy of this film.
In what some would call the greatest piece of film-making that’s ever existed (no reference available because literally no-one has ever said this), the story follows the escapades of three very unlikely travelling companions as they migrate to warmer climes ahead of a coming ice age. Although it’s a sweet story about friendship and bravery and adventure, the film is factually steeped in paleoscience. The coming ice age depicted in the film is actually part of Earth’s most recent glacial period, which took place in the dying days of the Pleistocene epoch. I must admit to some naivety here - I had never before considered the possibility that there was more than one ‘ice age’ (as in the glaciation event, not the movies - although, Dreamworks really should have stopped after number 2).
Firstly, it’s important to distinguish between the terms ‘ice age’ and ‘glaciation’. The term ice age is used loosely, and most people understand it to mean that 11 500 years ago, large areas of land were covered in snow and ice. More correctly, this period is actually the ‘Last Glacial Maximum’, where the average global temperature was approximately 8°C. And it’s called the ‘Last Glacial Maximum’ because in the Quaternary Period alone, there have been 7 complete glacial-interglacial cycles. Basically, that means that Earth is constantly moving between colder periods, where glaciers advance (a glacial period) and warmer periods (an inter-glacial period). This shift is caused in part by variations in the Earth’s orbit around the sun, which determines how much energy is received from the sun, as well as upon which hemisphere this energy is predominantly concentrated. Currently – and thankfully – we are in an inter-glacial phase, but over the last 850 000 years, we’ve cycled through some much colder times, where vast areas of Earth were covered in ice.
Ok, but how do they know?
For those of you who don’t know, in my spare time, I’m a high-school geography teacher. And let me tell you, “but how do they know?” is by far the most commonly asked question in my classroom. There must be something about the brain chemistry of a 15-year old that causes them to doubt everything they hear. But I will admit, it’s a valid question. How do they (paleo-scientists that is) know when glacial periods occurred?
Turns out, my Grade 12 science teacher was right – isotopes are important! More specifically, the δ18O and δ16O isotopes found in polar ice, and seafloor and lake sediment. These handy little isotopes of oxygen reveal the conditions under which precipitation fell, many millions of years ago. They are also present in diatoms – which are photosynthetic algae that form shells. By analysing sediment cores from lakes, scientists are able to establish the ratio of δ18O and δ16O at the time that diatoms formed their shells, which indicates the state of the climate at that time. However, whilst diatoms are a very useful indicator of past climates, it is necessary to study 100% pure diatom samples, which are rare. Circumventing this limitation involves ‘cleaning’ the diatom samples, to remove organic material, carbonates, silt and clay, and other impurities. Whilst effective, this process does not allow for the separation of different diatom species. “What’s the big deal?” you ask, “Why would we need to separate the species of these tiny, ancient (dead) organisms?”. Well, science is all about the specifics, and the more we can refine research, the better. So, by sorting the diatoms into species, scientists could get a much better picture of the δ18O signature in the fossils, which would lead to a better understanding of the climatic conditions under which they formed.
Luckily, a 2023 breakthrough out of Japan saw the addition of a new tool to the palaeoclimatologist’s box of tricks. By using a laser to establish the degree of light scattering in a diatom sample, scientists were able to identify five separate taxa of diatom in a sample from the Southern Ocean. Because the laser beam highlights differences in size, shape and structure of different diatom species, it is possible to single out these diatoms and study them with far more specificity. This is a breakthrough in paleoclimate studies, as it allows for much more accurate measurement of the δ18O proxy, which translates to a greatly improved understanding of the climatic conditions under which each diatom formed. The methods presented in this study are also considered to be ‘simpler’ and faster than previously used methods, which really does mean a great deal in the science world.
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