I study how planets form, the creation of the early atmosphere and the degassing or release of volatiles likecarbon dioxide(CO2), hydrogen and sulphur dioxide from planetary interiors. In this process, noble gases are key. These are a group of inert elements they dont participate in chemical reactions. Carbon dioxide, nitrogen, hydrogen, etc., are chemically reactive but the inert nature of noble gases gives them an advantage in allowing these to keep a record of early events as no chemical reactions or biology alters them.

These offer information about planet formation. Among these, and especially among the heavier noble gases like krypton or xenon, some have many different isotopes which belong to the same element but have different numbers of neutrons. Some of these isotopes are produced by radioactive decay while some are non-radiogenic or not produced by radioactivity. The non-radiogenic isotopes allow us to look at different sources of volatiles on Earth while the others hold information on timespans and decay. They act as tracers of how fast things might be happening. They are the culmination of figuring out where gases are coming from and the rate at which a planet is forming.

BOTH STATIS FLOW: Lavas (R) found in volcanic regions like Iceland s Odadahraun highlands (L) bring materials up from Earth s interior to the surface these include noble gases which bear unalterable evidence of planetary processes, their inert nature resisting any changes. Photo courtesy: iStock


Most noble gases are in the atmosphere while some are also located in the planets interior, typically trapped in the crystal lattices of minerals. For atmospheric gases, missions like the Curiosity rover have measured their composition on Mars. There are also some measurements from Venus and new missions are meant to follow this. For Earth, we can sample the atmosphere quite easily for the interior, we need to rely on lavas or melts which come up to Earths surface, bringing gases with them. When they solidify, these melts trap bubbles inside them noble gases are often found in these tiny bubbles. We study these by crushing samples apart in our lab and doing measurements using mass spectrometers. For other planetary materials like asteroids or meteorites, we often find gases trapped in the crystal lattices of minerals present there we use heating techniques to release those and mass spectrometers to measure them.

Xenon is a noble gas it has nine separate isotopes. Of these, many are produced by the radioactive decay of three separate groups of elements, uranium, plutonium and iodine. Uranium is still around in the solar system and on Earth. Naturally occurring plutonium was present in the early solar system and Earth but has become extinct now, having all decayed away. The same is true of radioactive iodine, which was in the early solar system and our early planet but which hasnt completely decayed yet. So, xenons isotopes could only have been produced during certain times in Earths evolution whereas other isotopes are still being produced. Some are not even produced now they only come from stellar burning in stars. So, these different processes and their diverse timescales allow us to look at the history of planet formation. Examining a certain isotope tells us this had to have been produced maybe in the first 100 million years of Earths existence it couldnt have come later on. That puts a firm timestamp on when a certain process, like a melting event or the formation of the moon, might have happened.

LUMINOUS:Isotopes indicate the moon's age. Photo courtesy: iStock


We also study feedbacks or linkages between Earths surface and its deep interior. We try to address how the rates of volatile exchange have changed through time this includes noble gases, water, CO2 and nitrogen. Water and CO2 play a vital role in making a planet surface habitable we now know that CO2 is very important in producing the greenhouse effect, too much of it is harmful while too little also makes a planet uninhabitable. We can study this not by directly looking at CO2 but rates of noble gases which are used as a proxy to tell us what other gases are doing. We look at how much interior degassing rates have changed as Earths interior cooled and how much of these gases were recycled back through time if there were no recycling, wed expect the surface inventory of these gases to keep growing through time. But if there is recycling, we see a balance between whats coming out of the interior and what is going back into Earth through plate tectonics. The balance between the outgassing and recycling of volatiles is important in keeping Earths surface habitable.