What are Isotope Geochemistry and Cosmochemistry? – Interplanetary Crime Scene Investigation
Since we are starting a blog about isotope geochemistry and cosmochemistry, we should talk a little about what these exotic subjects are. We and others research groups like us use isotopic abundances of elements and the chemical properties of elements to work out how the Earth and solar system bodies were formed and evolved and what materials they were made from. It is a sort of interplanetary CSI since we are trying to piece together what happened when the sun and solar system formed and all we have to go on are subtle clues long after the crime.
The forensic material available for study on Earth is much wider than most people realise. We have available – grains that are condensates of distant stars from a time before the solar system was born, materials condensed in giant molecular clouds that form stars, grains from comets, interplanetary dust particles, solar wind, asteroid grains, a huge variety of meteorites and Martian and lunar rocks. All contain the elements we are familiar with on Earth but in different amounts compared to what we are used to on Earth.
In particular we look at isotopes, varieties of atoms of the same element but that weigh different amounts. By looking at the exact abundances of the different isotopes of an element then much can be worked out about what the original material was that went to form the solar system and the processes that have altered it since. In trying to work out where we all came from, then interstellar grains in particular are our prime evidence. Interstellar grains are micron-sized (only a thousandth of a millimetre) grains of different minerals that are true condensates of stellar winds and supernovae explosions. They are samples from distant stars that died before the sun and solar system formed. Some of these have been discovered hiding along in amongst the mineral grains that make up the bulk of certain types of meteorites. The amounts of different isotopes of carbon, oxygen, nitrogen and silicon are hugely different to what we find in the solar system and on Earth – which is how we know they came from different stars and give us clues about what some of the material was that formed the solar system that got mixed up in the giant blender that was the forming solar system to form what we see today.
In future posts we will be discussing more about how we go about analysing these types of samples and what we are learning from them.