Planet Earth Online

A new view of diamonds, bones and minerals

18 August 2008

At the rear of the University of Edinburgh's Earth Science Department lies a basement humming with expensive-looking machinery, the likes of which you might expect to see in a sci-fi movie. These are the UK's only two ion microprobes dedicated to environmental research. They can analyse the composition of diamonds, minerals, glasses, shells or bones.

The beauty of this technology is that it can target minute areas making it ideal for scientists studying samples that are particularly rare, hard to extract or complex. The microprobes work by firing a beam of electrically charged atoms (ions) at the sample, causing the ejection of their own ions which then separate and are detected according to their mass. That way scientists can measure exactly what elements are present.

Although the high-tech machinery is remarkable, the real value of the facility lies with three people, John Craven, Richard Hinton and Simone Kasemann, whose hard work, enthusiasm and dedication have helped hundreds of scientists over the years tackle a variety of earth and environmental research projects. The projects range from understanding the deep Earth and volcanic hazards to environmental changes in the Earth's system.

I spoke to some of the people using the facility to find out a little more.

The formation of Earth: understanding magma in the mantle

Natalie Starkey wanted to find out whether lava flows found on West Greenland and Canada's Baffin Island were produced by the same volcanic event 60 million years ago. To understand how these two flows were produced, she used the ion microprobe to measure minor element compositions from tiny pockets of molten magma trapped in crystals in the lava. These crystals preserve a record of the evolution of the magma. She combined these data with previously measured helium isotope ratios from similar magma pockets.

Natalie's research has led to something quite unexpected - the discovery of ancient materials from the time of the Earth's creation in relatively modern lavas.

Helium was trapped in the Earth when it formed about 4.5 billion years ago and since that time it has slowly seeped out of the Earth's mantle into the atmosphere. Natalie looked at the chemical indicators of the Earth's evolution and a particular type of helium isotope no longer produced today. When researchers find this isotope, they know it has been preserved since the birth of our planet. To her surprise, she discovered the highest helium ratios known from any volcanoes on Earth were in these lavas.

Analysis of these miniscule trapped magma pockets enabled Natalie to show that parts of the mantle have been left pristine since very early in Earth's history. Almost all other lavas come from mantle which has been processed several times over.

Natalie said, 'My research suggests that there's still quite a lot of helium left in the Earth so I need to work out why we have parts of the Earth which haven't given up this gas. The helium I found in the lavas is very primitive; it might have come from magma which has been stored away somewhere deep near the boundary between the core and the mantle since the Earth's formation.'

This work provides an exciting new insight into how the Earth's mantle might flow and mix, but needs further multi-disciplinary research to piece all the evidence together and create a possible model and explanation for what is happening.

Releasing gas: understanding magma in the chamber

Emma Passmore has been studying the magma chambers that fed large eruptions on Iceland. Her work allows scientists to better understand volcanic gas release and to help people produce early warning systems for future eruptions.

Emma focused on Iceland's most notorious eruption that spilled vast quantities of molten basalt lava over an eight-month period in 1783. The Laki eruption released so much noxious gas and ash that much of the livestock died, leading to widespread famine. About a quarter of the people living in Iceland also died and the effects were felt across northern Europe for years afterwards.

Emma and her supervisor, John Maclennan, decided to find out how volatile elements carried in the magmas from deep in the Earth were mixed in the magma chamber and subsequently released as volcanic gases. Using the ion microprobe, they measured the tiny amounts of trace and volatile elements held within olivine crystals. These crystals grew in the chamber as the magma cooled, occasionally trapping small pockets of molten magma within them. These pockets act as a window in time telling us not only what elements were present, but also about the physical processes which led to the formation of the magmas.

Emma found that the magma's composition was variable in the chamber but not in the erupted lava. She said, 'Before the lava is erupted, you have a massive physical mixing and stirring to make it really homogenous. It's a bit like two pots of paint which need to be thoroughly stirred so that the paint filaments come close enough to diffuse and a new colour is blended.'

By understanding this mixing, and knowing the depth of the chamber, Emma has quantified the gas release for this eruption. She found that some gases were released long before the eruption took place.

John said, 'I hope that we can eventually use these sorts of measurements to develop an early warning system. We could compare measurements of present day gas release to how much we knew was released in the years leading up to the Laki eruption. Laki-like eruptions happen every few hundred years and it would be good to know when the next one is approaching.

Ancient shells reveal past ocean acidity

Daniela Schmidt is using the ion microprobe to determine the acidity (pH) of past oceans. She has documented pH levels over periods of about two weeks to a few years. This doesn't sound too remarkable until we learn that these short periods took place some 55 million years ago.

She does this with the help of tiny marine organisms called plantkic, surface- ocean-dwelling foraminifera that have a life-span of about two weeks. During this time they build shells by depositing carbonate and other trace elements. The amount of different trace elements they deposit depends on their biology and also the surrounding marine environment. So by understanding their biology and looking at the composition at various points of the shell, we can tell the state of the sea and how it influenced the organism as it grew - a bit like looking at the rings in a tree trunk.

Millions of tonnes of these organisms live in the oceans; when they die they sink to the sea floor. Over time, sediments build up and they eventually form rock - the tiny shells preserved as fossils. By drilling and collecting cores from the deep sediment of the seabed, scientists can use these shells to unravel the history of past oceans. This science isn't very new but what hasn't been achieved until now is a documentation of the ocean's acidity and its rate of change during the mass extinction 55 million years ago.

Daniela said, 'We know this was a time of rapid global warming and that carbon dioxide levels in the atmosphere were high. The world changed considerably and it was a disruptive time for both marine and terrestrial life.'

The oceans rapidly became acidic; so much so that the majority of foraminifera shells on the seabed simply dissolved. The lack of fossil evidence has been a stumbling block for scientists trying to work out the how the pH of oceans changed. The problem was that scientists traditionally needed lots of shells to analyse but thanks to the ion microprobe facility, Daniela documented the change of pH levels using just a small number of intact shells.

Our seas are rapidly becoming more acidic. We need to look to similar events in the past to know whether we face another mass extinction of marine organisms in the future.
Daniela and collegues have now estimated the rate of change in pH levels in the ocean 55 million years ago and has compared this with current conditions. Planet Earth will report these findings later in the year.

Keywords: Environmental change, Geology, Hazards, Natural resources, Oceans,

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