Unravelling the Earth past using stable isotopes

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.

Isotopes

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

Introduction to Classical Mechanics by Stephen Hughes

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Introduction to Classical Mechanics by Stephen Hughes

Gravity, a natural phenomenon that keeps our feet firmly on the ground and occasionally permits us to have our heads in the clouds, shapes the Universe by binding vast systems of planets, stars and galaxies together. It is also responsible for the Earth’s dynamic tides and causing apples to fall from trees. Yet it is the weakest of all the fundamental forces that govern how everything interacts with everything else. The other three forces are the strong force, electromagnetism and the weak force, in order of decreasing strength. The strong force binds protons and neutrons together forming the nuclei of atoms. Electromagnetism is responsible for electric charges attracting and repelling one another. This also includes the similar effects experienced by magnets. The familiar behaviour of this force is how opposites attract and likes repel. Finally the weak force, still far stronger than gravity, causes radioactive decay. Why then does gravity have such a big impact on the dynamics of the Universe? The answer to this question has two parts. Firstly the strong and weak forces act only over very short distances, about the same distance as the size of an atoms nucleus. Secondly, although electromagnetism has an infinite range it acts on objects that have either a positive or negative charge. There are usually an equal number of positive and negative charges in a given region so any overall effect cancels out. Gravity in comparison has an infinite range but acts only on objects that have mass, which is always positive. This is how gravity triumphs in governing the large scale dynamics of the Universe. Only one type of mass, positive mass, means gravity causes everything to be attracted to everything else.

When Isaac Newton described gravity mathematically he provided a method to calculate the future position of the planets, the height of the tides and eventually helped land a spacecraft on the moon. The downside to his description is that it gives no indication of how gravity works. What mechanism causes two objects with mass to be attracted towards each other? As astronomical measuring instruments improved it was observed that the predictions regarding Mercury’s position were slightly wrong. Albert Einstein had been thinking about gravity and was interested in this problem with Mercury. His new theory of gravity, general relativity, accounted for this small difference and calculated the correct position of Mercury. It does this by incorporating the strong gravitational effects experienced near to very heavy objects, like the Sun. Mercury, being the closest planet to the Sun, is affected more than any other planet in the solar system. General relativity also gives us an insight into the mechanism that makes gravity work. Space is described as distortable, compressing and stretching in the presence of mass. Space warps around an object with mass, which causes a passing object to follow the shape created by the warped space, giving an illusion of a force acting between the two objects.
Stephen will be leading a fascinating course by Continuing Education titled an Introduction to Classical Mechanics: The Origins of Science from Wednesday 1 October – http://payments.liv.ac.uk/browse/extra_info.asp?compid=1&modid=2&catid=33&prodid=509