Interview Professor Kathy Whaler
Magnetic field personality…
Interview Professor Kathy Whaler
Magnetic field personality
Professor Kathy Whaler tells non-scientists her work is all about knowing “why the compass points north,” but her research in geophysics goes a lot further than helping our map-reading skills – it has advanced our understanding of the Earth’s magnetic field and helped us map our planet (from the core to the surface) as it formed over billions of years...
It may seem strange to name an asteroid in honour of a scientist who is more concerned with looking down towards the centre of the earth than gazing up at the sky, but there’s a perfectly rational reason – this chunk of space debris (5914 Kathywhaler) can actually tell us a lot about the core of our planet and the dynamic processes going on thousands of kilometres under our feet.
Kathy Whaler, who is now Professor of Geophysics in the School of GeoSciences at the University of Edinburgh, is also a former President of the Royal Astronomical Society (2004–2006), but even though non-scientists may wonder why a geophysicist has such a strong connection with astronomy, for Whaler this makes perfect sense. “The province of geophysicists has gradually expanded to encompass some of that formerly occupied by astronomy,” Whaler explains. “We can now apply geophysical techniques to astronomical objects. There’s some overlap in approach, too – in both cases, we can only observe what’s there, rather than alter conditions and then repeat the measurements as you would in a lab experiment.”
The links between the different scientific disciplines get stronger all the time. Over the last 30 years, geophysics and geoscience in general have increasingly employed a multi-disciplinary approach to research, including the analysis of data from satellites scanning the Earth and the planets beyond, as well as taking advantage of dramatic advances in computing resources which enable the construction of extremely complex models of the Earth. The work of geophysicists is never far removed from pure mathematics and physics, especially when they are trying to answer big questions such as how our dynamic Earth functions – powered by energy that drives a dynamo deep in its core.
Whaler explains that the inner core of the planet is a solid mass (primarily an iron–nickel alloy) about 1,200km in radius, possibly rotating at a slightly different rate than the rest of the planet, surrounded by a similar-sized outer core – a circulating “ocean” of liquified iron with the same viscosity as water. As the Earth cools, the liquid iron in the outer core slowly solidifies, adding to the volume of the inner core. These dynamic processes are a huge source of energy that plays a key role in the generation of the Earth’s magnetic field, and this was the focus of Whaler’s research as a PhD student at Cambridge in the late 1970s – using geomagnetism to study the dynamics of the Earth’s core and deep mantle, “to explain how the geomagnetic field evolves over time.”
Trying to understand the structure of the planet is also not unlike pointing a telescope up at the stars in the sky – it is a highly complex, puzzling phenomenon, but it also has to be studied in similar ways, with instruments that help light up the “darkness” down below.
In simple terms, Whaler’s work involves mapping the core, measuring the strength and geometry of the magnetic field to build up a picture of what lies under the surface – much like an X-ray of the human body or detecting radiation from “invisible” stars.
In the outer core, the liquid iron moves around like water boiling in a saucepan, and this convection generates the Earth's magnetic field. The strength of the magnetic field at various times in the past has been recorded in rocks, which also record the reversal of polarity (from north to south and vice–versa) which takes place every few hundred thousand years, thus helping us to date the rocks.
The Earth's magnetic field is not just a good tool for seeing what's under the surface. It is also important because it protects the atmosphere from being destroyed, by deflecting the Solar wind – a stream of particles which radiates out from the Sun and sometimes interferes with radio communications and GPS signals, etc.
For her PhD, Whaler came up with an innovative method to explore whether there was a “stagnant layer” at the top of the core where the dynamo wasn’t operating. This novel approach allowed her to use magnetic data to study the flow of the liquid iron there. “Normally, there are too many unknowns for us to infer the flow, but if the convection (over-turning motion) was not making it all the way up to the core surface, then the flow is simpler,” says Whaler. “We could test whether the data were consistent with the existence of this stagnant layer and, having found they were, then go on to discover the geometry of the flow.” Suddenly, the geomagnetic data were a powerful tool to probe the workings of the dynamo.
Other scientists later made different assumptions about the flow which could also be tested for consistency against the data. Interestingly, although each implied a different dynamical situation, the flow geometry inferred was very similar. About two years ago, new estimates of the properties of iron at these extremely high temperatures and pressures suggested convection was unlikely to extend all the way through the outer core. “This new research suggests my idea is more probable,” says Whaler.
In the 30 years since Whaler first developed her theory, geomagnetism – and geophysics in general – has gone through an era of rapid advances in the use of technology. This has helped prove many long-standing theories, but also created new intellectual challenges, simply because of the vast amounts of data now available.
It is useful to know that it was not until about 1840 that scientists devised a way to measure the strength of the Earth’s magnetic field. Prior to that, we only had information about the direction in which it pointed. These directional data were recorded routinely by sailors in ships’ logs for navigational purposes, and have recently been “mined” by scientists to reconstruct models of the magnetic field dating back several centuries, making an educated guess about its strength prior to 1840.
Satellite data have also revolutionised our view of the planet. For example, says Whaler, ”MAGSAT (launched by NASA in 1979) provided a very detailed picture of the magnetic field even though the MAGSAT data did not ‘prove’ any theory. However, because the picture it provided was very similar to models of the older magnetic field, it gave scientists the confidence to believe them.” The data gathered by MAGSAT over seven months was a “revelation,” she adds, because until then we relied on sparse data from the 100 or so observatories scattered across the globe, including two in Scotland (Eskdalemuir and Shetland).
Advances in our understanding of geophysics can be very slow (there are very rarely any “quick fixes” in geoscience), but knowing more about the ancient past and what is happening now can be a good guide to the future, and possibly help in forecasting and mitigating a catastrophe or locating valuable resources such as minerals and hydrocarbons.
One of Whaler’s major interests at the moment is her work on the Afar Rift Consortium project in Ethiopia, the only place in the world where three tectonic plates meet on the surface of the planet above sea level, at the northern end of the 3,000km-long East African Rift Valley, which will eventually form a new ocean when the rift grows wide and deep enough for seawater to flow in. Normally, the plates there move apart at a rate of about 15mm a year, but in one area in September 2005, there was a period of dramatic earthquake activity when they shifted eight metres apart in a couple of weeks, as magma forced its way in over an area 60km long by 8km deep, forming what is known as a “mega-dyke.” This has provided an unprecedented opportunity to study how new crust forms, using the latest technologies including satellite data.
Whaler’s specialist area for this project is magnetotellurics (MT), imaging the earth’s subsurface by measuring variations of natural electrical and magnetic fields at the Earth's surface. The different electrical conductivities of rocks and sub-surface fluids affect how the electromagnetic (EM) waves propagate, so measuring and mapping the EM fields at the surface helps infer rock type, sedimentary layer thicknesses, and the presence of magma, etc. It can also help to identify the presence of hydrocarbons, water resources (including those used to generate geothermal energy), and particular minerals and precious metals, even deep down in the crust of the Earth.
The international team of scientists in Ethiopia (funded in the UK by the Natural Environment Research Council) is studying how the Earth’s outermost shell, which is usually about 40km thick, has been stretched, thinned and heated to breaking point, allowing the magma to force its way up towards the surface. Whaler is looking for highly conductive magma and partially molten rocks, and by measuring the variations in conductivity, she is able to map the “ponds” or pockets of magma under the surface, while others observe how it is moving and forming new crust, including intruding the 2005 mega-dyke and 12 smaller subsequent dykes.
Whaler works very closely with many other specialists to see the “big picture,” including petrologists who study the chemistry of rocks erupted at the surface and can add a lot of detail to her magnetotelluric image of the crust – they determine how much water and various key minerals the magmas contain, and also how hot they were, which controls their electrical conductivity. This helps her to measure more precisely how much magma is stored down there.
This multi-disciplinary research is a long way from the early days of Whaler's career, but reflects the way technology continues to have a huge impact on geoscience and helps to advance our understanding of the planet – and other planets beyond.
For example, another of Whaler's big passions is remote exploration of Mars, using data from the Mars Global Surveyor (MGS) satellite to study the magnetic field and find out if the planet developed the same way as ours, undergoing reversals of polarity which suggest plate tectonics and similar formation of the crust.
The work of geophysicists may seem to be a “slow-burner” but Whaler is a passionate evangelist for geoscience in general. Many of her students have gone on to different careers which may not directly use their specific geoscience training, but do take advantage of the various disciplines and skills learned in the course of their studies, while others have gone on to work in hydrocarbon exploration and mining.
Applications which make lots of money are not the only measure of value, however. When the poles reverse again (the last time was 700,000 years ago and there are signs it is starting to happen again) and our compasses don't work, we will all want to know what it means. And as Whaler and her colleagues find out more about what lies beneath our feet, it will not just advance our understanding of the natural hazards which threaten life on the planet, but also our ability to detect new resources that could make life better.