So, I'm with Professor Ray Burgess, who's professor of isotope geochemistry here at the University of Manchester, and I wanted to find out about isotopic ratios, and how we can use the ratios of different isotopes within a substance to understand physical processes within the Earth's system. So first of all, what are these isotopic ratios, and how do we use them? >> Okay, so some isotopes are what we call stable isotopes. They don't undergo radioactive decay. And the variations in the isotope ratios that we measure for these group of isotopes result from chemical and physical processes, and the reason why we get isotope variations is related to the mass of the isotopes. So these are what we call mass dependent isotope variations. So if you think of an example, the hydrogen isotopes. There are two hydrogen isotopes, hydrogen-1 and then hydrogen-2, which has a special name, deuterium. So there's hydrogen-1 and hydrogen-2, and the relative mass difference between them is 100%. So the magnitude of the isotope variations that we measure is related to the mass difference. So the hydrogen isotopes that we measure are variations, naturally occurring, which are probably larger than any other element. >> So when I look at the literature, I see people write about and say, so much percent of the hydrogen atoms in the universe are composed of hydrogen-1. So much percent are composed of hydrogen-2, but seems to me what you're saying is that these ratios, I mean that's a kind of a global ratio, but within individual substances those ratios may differ from the average. >> That's right and the reason for that is that they will change in response to chemical reactions. Particularly, biochemical processes will fractionate. Changing the ratio we call fractionation. They will fractionate the isotopes. Reactions that go on in cells in our body will tend to concentrate the low mass isotope into the products of any biochemical reactions, and that's one of the major ways of fractionating isotopes on Earth. But you can also fractionate isotopes during physical processes as well, so for example during the evaporation and condensation of water. The oxygen and hydrogen isotopes in the water will become fractionated. And also, probably most important, is that all isotope fractionations that occur like this are temperature dependent. And curiously, the magnitude of that change, that fractionation, is larger as the temperature decreases. And this makes isotopes very good thermometers. >> Hm. So one way that I've seen this displayed in the literature is taking an ice core, say, and then there's a graph with depth of the relative ratios, of I think it's the oxygen-18. >> Yeah. >> And then so the wiggles in this curve from either high oxygen-18 concentrations to low oxygen-18 concentrations indicate something about the temperature of that ice core or the environment? >> Yes, that's right. So probably the most important application of stable isotopes in geology has been in the area of climate science, particularly working out past climates. So they can apply to a whole range of climate archives, similar to what you suggested. Ice cores, but also ocean sediment cores, cave deposits, lake deposits. Well, a whole range of things, really. And this is probably the most important way of interrogating the earth's past climate using stable isotopes over thousand-year to billion-year time scales. >> And so by looking at these records then, we can see these as you said, the relative highs, relative lows. And then these relate to warm, cold periods in the Earth's climate. And if we look at the biological things, we can determine the presence of active or inactive biological periods as well? >> Yes, that's right. And we can also establish the links between what's happening in the terms of how much biological activity there is at any point in the past, with the amount of inorganic activities going on and there's a very fine balance between the two. So when you start increasing the levels of biological activity, it has affect on the sort of inorganic process, for example, that go on in the ocean or in the earth's atmosphere. So you can interrogate these records, you can work out the relative balance by looking at the isotope variations through time. >> What's an example of the way that you've used these stable isotopes in your research? >> So, an example here is on the screen just behind me here where we've been looking at some climate records, which have been contained in fossil hydrothermal systems. So these are essentially hot water that's been circulating around hot igneous rocks in the geological past. >> In the mid ocean ridges or, >> No, these are in Antarctica. So here we're looking at Antarctic climate conditions between about 20 million years ago and about 50 million years ago. Which is a critical time, because it's the time when we went from being fully non-glaciated, to conditions where we now have polar ice caps. >> Excellent, so thank you so much for your time and good luck. >> Thank you.
