Unravelling the Earth past using stable isotopes
By Tsvetomila Mateeva & Nealy Carr
Everything around us is made of atoms of different elements. These tiny nanoscale particles are the building blocks of matter and life itself, the plants, the animals, the rocks, the stars the whole universe, the air we breathe and indeed you and I and everyone else. Since the dawn of time, people have wondered about the origins of the Earth, and the study of chemistry has helped answer some of these questions and given us great insight into the secrets of Planet Earth.
Science is constantly evolving and history is marked by great breakthroughs that allow us to progress and enable us to see and understand our world more and more. One such discovery was the discovery of the stable isotopes. Some of the first traces of the notion of isotopes go back to the beginning of the 20th century (around 1913), when the scientists Kasimir Fajans and Frederick Soddy, independently of each other, made the conclusion that atoms of the same element but with different masses exist. The term “isotope” we use nowadays however, was given by Frederick Soddy.
Isotopes of an element have the same atomic mass, the same number of protons and electrons, but can be lighter or heavier depending on the number of neutrons. It is this difference that enables chemists, biologists and physicists to explore, understand and answer questions that have eluded us in the past.
The application of a stable isotope approach is a powerful biogeochemical tool, and the ratio between the heavy and light isotopes of different elements are commonly used in earth science, archaeology, food safety and forensic science. For Example:
• Light isotopes of gases such as oxygen and hydrogen are well understood and used in geochemistry to trace the geographical source
• Carbon isotopes are used to differentiate organic and inorganic matter which in turns helps us reconstruct past conditions for life on Earth
• Oxygen isotopes are used as a planetary thermometer from which we can determine the temperature and climate of the past
• Boron isotopes are an indicator of the acidity or pH of our paleo oceans
Most part of us knows some TV criminal series, such as CSI, where the characters often use chemical analyses to find more information about the crime scene and determine who is guilty. Unfortunately in the real life the things don’t happen so fast and as accurately as in these series. Despite this fact, we try to apply these techniques in many cases. They could help determine the authenticity of a food – is a maple syrup a real one or is it made of corn or sugar syrup (carbon isotopes); are the vegetables you bought last week from a local farmer (hydrogen and oxygen isotopes)? The stable isotopes could give us a satisfying answer to these kinds of questions.The many applications of stable isotopes methods in the modern society.
The picture is from the august issue magazine Elements explaining the social and economic impact of the geochemistry (Ehleringer et al., 2015)
If you would like to learn more about this fascinating subject Tsvetomila & Nealy are running a brilliant short 5 week course Unravelling the Past: A Geochemical Approach from Wednesday 13 April – you can read more about this course and book your place here http://goo.gl/bENazU