By Pat

Eleanor’s post last week on scale provided the perfect segue for my first ever blog (!). Like many people when I think about my work, I find it useful to visualise processes to better understand them. I do this when I think about the interactions of atoms, tectonic plates and planets for example. In geoscience it seems we often work on scales that are either too small to see or too large see all at once (or at all) and thus an imagination is vital. It is a misconception that creative people study arts whilst regimented people study science.

Studying geology, or any science for that matter, requires imagination to both visualize interactions on different scales and to hypothesize new interactions or new angles to old problems. In science, our imagination is grounded in fact; we have anchor points or truths that we have to incorporate. In a vague metaphorical way it’s like we are creating our own “connect-the-dot” pictures, where the dots represent our current knowledge but it’s our imaginations that dictate the lines (see figure below).

Two interpretations of a simple connect-the-dots game. The artist on the right may be cheating by visiting the same point more than once, but i think my point is still valid.
Two interpretations of a simple connect-the-dots game. The artist on the right may be cheating by visiting the same point more than once, but I think my point is still valid.

Indeed it takes a great deal of confidence to be imaginative in the sciences – where physical laws can be so restricting. However I believe the greatest breakthroughs in geoscience probably originate from the greatest imaginations. Similarly, for me at least, the most exciting science is where there are fewer facts and thus the most room for imagination and innovation (e.g. the creation of the universe, search for life, or the origin and evolution of mineralising fluids in tin systems as indicated by tourmaline and cassiterite chemistry). At times however, in particular when we are trying to understand the basic principles behind these facts, I believe it is helpful to be able to see the processes, rather than having to imagine them. In my studies, most of this is happening at the atomic scale which, as you can imagine (haha) is hard to see. A large component of my PhD involves radiometric dating using the U-Pb decay system. We can date rocks in this way because we know that 238U decays through a series of different isotopes at a known rate¹, until eventually it stabilises as 204Pb (see figure below). Thus if we measure the amount of 238U and 206Pb in a rock or mineral we can estimate its age. Incidentally I noticed that this blog page already has a summary of radiometric dating here.

Decay chain of U and Th isotopes. Time taking to decay from each isotope is in brackets. a= ,
Decay chain of U and Th isotopes. Time taking to decay from each isotope is in brackets. Thanks USGS for the image.

Until last week I regarded this decay as one of those processes I could only imagine. However recently, whilst doing some YouTube ‘research’ I came across the following riveting video:

It is an experiment in what’s known as a “Cloud” or “Wilson” chamber which is supersaturated in water vapour or alcohol and sealed. Any form of ionizing radiation within the chamber will cause local ionisation of the gas and result in condensation and the formation of mist. If you put a large chunk of highly radioactive U metal in this chamber the radiation emitted every time an isotope decays through the sequence (as shown in above figure) it emits radiation, resulting in the formation of a trail of mist. The video is ~50 minutes long, and I highly recommend getting yourself a bag of popcorn and a choc top and enjoying the entire show. To make it an extra special occasion bite off the outer chocolate layer and then dunk the choc top into the popcorn so that the popcorn sticks to the ice-cream. If you then eat the popcorn with the light ice-cream spread you will remember the true meaning of happiness.  But if you’re in a rush, just skip to ~5 minutes in to see the main action scene where radiation is being emitted continuously and in every direction. Incredible. Whilst this experiment used mostly pure U metal and thus is a lot more intense than anything you would see from a natural sample, it helps visualise a few important aspects of my work.

Firstly this is why we don’t go near radioactive stuff.

Secondly, each trail flying out from the sample effectively represents another tick (or tock) in the U-Pb radiometric clock. As the isotope decays it releases particles and radiation. In this highly radioactive sample decay is happening vigorously. Theoretically those trails would continue to form for billions of years, however over the course of the experiment alcohol begins to condense on the U metal.

Thirdly, and building on from my first point, it illustrates the amount of heat that can be generated by radioactive decay. A large proportion of Earths heat is generated in this way in the mantle and crust. This heat has huge implications for both mantle convection² and many crustal processes (including forming hydrothermal mineralising systems – which is why I care).

Directly observing all the processes we are or will be interested in is (surely?) impossible, and in these situations it is useful to visualise what is going on. When we do get the opportunity to witness something I believe it is an incredible tool for both understanding and educating others – which ultimately is what can spark the imagination and lead to breakthroughs in our knowledge. As Albert Einstein put it,

“To raise new questions, new possibilities, to regard old problems from a new angle, requires creative imagination and marks real advance in science.”

In conclusion, never underestimate the Youtube database.

¹As it turns out, this known rate is not so well known.

²As I understand this is still up for debate.