T-minus 2 weeks (ish)

by e_e_evans PhD student

An introduction

featuring: scientific definitions, explanations and some welsh

I thought I’d begin this blog as a slightly more formal and semi-professional way of sharing my journey into the great wide unknown of postgraduate academia. Most who I speak to on a face to face basis (or even a Facebook to Facebook basis) will know that I will soon be starting a PhD at Swansea University (or Prifysgol Abertawe as the lovely Welsh would have it).

But before I start it might be fun for me to explain in plain English what on Earth Swansea University agreed to give me money to do.

My actual PhD title is: “Deciphering the processes affecting volcanic ash deposition within sedimentary environments using X-ray microtomography and mu-XRF techniques” (probably subject to change on the actual thesis cover). I’ve settled for “climatology”, “studying deep-sea sediment cores” and even (desperately) “x-raying rocks” as a description to non-geologists, but the beauty of a blog is that I have a captive audience a bit more time to explain what it really is.
So here we go…

As we all know from a month or so the other year where all the news readers struggled to pronounce an Icelandic word and everyone’s holiday fights were cancelled volcanoes produce ash which spreads a very, very long way from the source. The result is that a lot of it gets laid down in the ocean sediment near the volcano. We’ve all walked on a sandy beach and know that it’s covered in ripple marks and shifting pebbles not millions upon millions of previous footprints. The sediments move and when you have a layer of ash that has settled out onto your sediment there’s a chance that will move too. (Thus explaining the first 10 words of the title).

The next bit is a little more “science-y” but put simple X-ray microtomography uses exactly the same principle as medical CT scanners. It uses X-rays to build up a 3D picture of an object without the need to destroy it (useful for rocks and life-saving for people!) These images then can be studied and manipulated to look at the different materials that make up the sample using contrasts in density. mu-XRF or to give it its full title, micro-x-ray fluorescence, once again uses x-rays but instead of firing them through the sample and detecting the resulting contrast, XRF looks at the radiation emitted from the sample being excited by the X-rays. Kind of like how a fluorescent light works.

Your final question of course is ‘what is all this in aid of?’. That answer is actually the easiest bit. We’ve all seen those climate change graphs that show how the Earth’s temperature has varied over time. The way those graphs are made is by looking at so called proxy data, information that indirectly tells us about things like temperature or carbon dioxide. But there’s a flaw, what is needed is not just these data but when those proxies were laid down in the rock record. 10 cm of rock can represent a single winter flood or a million years and without absolute dates it’s just educated guesswork (there are methods we can use such as fossils which gives relative dates). Volcanic ash can be dated absolutely using radiogenic isotopes; atoms that are unstable and decay at a fixed speed over time. My work will make sure that the ash being dated is actually the same age as the sediments it is surrounded by because if it has been moved around, like those pebbles on the beach, the dating could be out by hundreds or thousands of years.

I know that look a while to explain, I promise my next post will be a little more interesting.

I hope September is treating you well!