 Hi, my name is Jeff Bunning and I'm a PhD researcher here at the Research School of Earth Sciences at the ANU. Most of the time I'm studying a really primitive group of meteorites called the chondrites from the very early solar system. And part of the way that we know that they're from the birth of the solar system is by radioisotope dating. And that's what we're going to be looking at today. And radioisotope dating are a set of techniques that can tell us about things from as far back as the beginning of the solar system, all the way up to archaeological dig sites today. To start with, to understand radioisotopes, we're going to need to know what an isotope is, let alone a radio one. An isotope is a version of the same element. There are multiple versions of them of slightly different masses. They all have the same number of protons. So with carbon, for example, we've got carbon-12 and carbon-13. Both of them have six protons. Carbon-12 though has six, well, carbon-12 has six neutrons while carbon-13 has seven neutrons. And that's similar throughout the periodic table. Now as a little aside, the word isotope comes from the Greek iso meaning the same and topos meaning place. So if you look at a periodic table, the isotopes all occupy the same space. You can't distinguish them using that table, which is why we have a whole special table called the chart of nuclides to be able to plot all of the isotopes of all the different elements against each other. We're not going to go into that today, but it's a very cool, very pretty looking plot. So we said that different isotopes have different numbers of neutrons in their nuclei. But you can't just start throwing in any number of neutrons or taking out any number of neutrons. If you start doing that, the nuclei start to become unstable. I imagine there's these big wobbly balls and they start to kind of like shake and shake themselves apart as the forces that bind themselves together either start pushing things out or become too weak to actually hold the entire thing together. And those types of isotopes, those ones that are unable to stay together are what we call radioisotopes or radioactive isotopes. They're unstable. And when they break apart or eject something, that's what we call decay. Now for any given radioisotope, how long it takes each nucleus to decay is random. But if we have a whole population of them, millions and millions of them, the time that it takes for half of that radioactive isotope to decay is really, really predictable. And that's what allows us to be able to calculate time with how much of it is left from a starting point. And the time that those half lives can take can vary from tiny minuscule fractions of a second to billions of years. And that allows us to build up a series of what we call chronometers if you want to, a series of clocks that work on different time scales. So this predictable decay is what allows us to date things, to get calculated radioisotope date by measuring the amount of unstable isotope we have in the object, often a crystal, compared to the amount of what we call the daughter isotope, the one that's at the end of the decay chain. And we measure the relative abundances of those. And by comparing those with some other similar decay chains and similar daughter isotopes, we can build up a isochron line. And that's something that we can, that is what gives us our age. Now radioisotopes are far more important than just clocks for a bunch of humans to figure out their place in the universe. Radioisotopes inside the earth are what keep it hot inside. And that is what drives the dynamism of the earth, our plate tectonics, volcanoes, things that are really important for life itself. But as well, one of the most important aspects of that is that it keeps the interior hot for the core. If our molten core were to cool, we would lose our magnetic field and we would lose the shield that protects us from the full brunt of solar and cosmic radiation and would wipe out life on earth as we know it. So radioisotopes are much more than just clocks. They are something that keeps this planet alive.