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Plate Tectonics and Ocean Drilling – Fifty Years On

Plate Tectonics and Ocean Drilling – Fifty Years On

What does it take to get a scientific theory accepted? Hard facts? A strong personality? Grit and determination? For many Earth Scientists today it can be hard to imagine the academic landscape before the advent of plate tectonics. But it was only fifty years ago that the theory really became cemented as scientific consensus. And the clinching evidence was found in the oceans.

Alfred Wegener had proposed the theory of continental drift back in 1912. The jigsaw-fit of the African and South American continents led him to suppose that they must once have been joined together. But in the middle of the century, the idea fell out of favour; some even referred to it as a “fairy-tale”.

It was not until the discovery of magnetic reversals on the seafloor in the early 1960s that the theory began to sound plausible again. If brand new ocean crust was being formed at the mid-ocean ridges, then the rocks either side of the ridge should show symmetrical patterns of magnetism. Fred Vine and Drummond Matthews, geologists at the University of Cambridge in the UK, were the first to publish on the idea of seafloor spreading in 1963.

But plate tectonics was still not the only theory on the market. The expanding Earth hypothesis held that the positions of the continents could be explained by an overall expansion in the volume of the Earth. Numerous twentieth-century physicists subscribed to such a view. Or, similarly, the shrinking Earth theory proposed that the whole planet had once been molten. Mountain ranges would then be formed as the Earth cooled and the crust crumpled.

Helmut Weissert, President of the EGU Stratigraphy, Sedimentology and Palaeontology Division, remembers the difficult exchanges that took place whilst he was a student at ETH Zürich in the late 1960s. “Earth-science-wise it was a hot time,” he recalls. “In Bern University they did not teach plate tectonics. We did not have a course on plate tectonics either. I probably first heard about plate tectonics in [my] second or third year.”

Weissert especially remembers Rudolf Trümpy, professor of Alpine geology at ETH at the time, saying that plate tectonics sounds interesting, but it does not work for the Alps. Meanwhile, younger voices at ETH, postdocs and lecturers, were becoming increasingly convinced by plate tectonic theory.

Weissert soon found himself in the midst of the controversy as his own research had a direct bearing on the debate. “I had an interesting diploma topic,” says Weissert. “I worked on continental margin successions and associated serpentinites.” Serpentinites are green-coloured rocks that are full of the water-rich mineral serpentine, and therefore must have formed on the ocean floor. The fact that Weissert was finding them in Davos, at the top of the Alps, was a good indication that modern-day Switzerland had once been part of the oceans. As Weissert succinctly puts it, “green rocks were ocean”.

The observed and calculated magnetic profile for the seafloor across the East Pacific Rise, showing symmetrical patterns of magnetism. (Image Credit: U.S. Geological Survey. Distributed via Wikimedia Commons)

By 1967, interest in the theory of plate tectonics had snowballed. When the Deep Sea Drilling Project (DSDP) was launched the following year, it had its sights firmly set on finding evidence that would definitively either confirm or reject the hypothesis of seafloor spreading.

The DSDP research vessel, the Glomar Challenger, set sail from Texas in March 1968. By its third leg it had drilled 17 holes at 10 sites along the mid-Atlantic ocean ridge and was already producing results that looked like they would confirm Wegener’s theory of continental drift. “After a few legs it was clear that the seafloor spreading hypothesis was tested and proven,” remembers Weissert.

There were only eight scientists on board, but two or three of them were working on the stratigraphy of the seafloor sediments. “The stratigraphy was superb,” explains Weissert. “You have the very young [sediments near the ridge] and then at the edges of the ocean the Jurassic sediments. If you have aging crust then you have aging sediment, so the hypothesis was very clear.” If the sediments got progressively older on moving away from the ridge, then so must the crust, a sure sign that new ocean floor was being created at the ridge.

Karen Heywood, EGU Division President in Ocean Sciences, remembers how her own fascination with the theory of plate tectonics ended up sparking her career in physical oceanography. Heywood began as a physics student at the University of Bristol in the 1980s. “They said we had to write an essay on the historical development of an idea in physics,” she recalls. “I did the development of the theory of plate tectonics and seafloor spreading. I wrote this essay all about Alfred Wegener.”

“This essay inspired me to think about earth sciences,” she says. “The idea that you could apply physics to the real world was amazing. It got me into oceanography.”

Heywood went on to establish her career at the University of East Anglia (UEA), where she became the first female professor of Physical Oceanography in the UK. “I went to the UEA and Fred Vine was there. It brought me back full circle. I could not believe that this was Fred Vine, who had discovered the magnetic stripes. This was the real person and that was amazing… it was the same person that I had read about and written about in my essay as an undergraduate in the 80s.”

There were clearly strong personalities on both sides of the debate about plate tectonics, but Weissert is pragmatic about the progress of science. “You have to accept that you are part of a scientific development. Everybody makes hypotheses… We all make mistakes. We all learn. We all improve.”

Indeed, many years later, in 2001, Trümpy wrote what Weissert calls “a beautiful small article” entitled Why plate tectonics was not invented in the Alps. Trümpy magnanimously writes, “Shamefacedly, I must admit that I was not among the first Alpine geologists to grasp the promise of the new tectonics.”  And yet, he continues, “to the Alps, plate tectonics brought a better understanding”. The humans and the science move on together.

By Tim Middleton, EGU 2018 General Assembly Press Assistant

References

DSDP Phase: Glomar Challenger, International Ocean Discovery Program

Trümpy, R., Why plate tectonics was not invented in the Alps, International Journal of Earth Sciences, Volume 90, Issue 3, pp 477–483, 2001.

Wildfires in the wake of climate change

Wildfires in the wake of climate change

Last year saw some of the biggest blazes in history, and may be a sign of things to come.

2017 was a record year for wildfires. California and neighboring western states saw the most destructive fire in US history, with an estimated 18 billion dollars worth of damage over the season. In central Portugal, fires caused 115 deaths over the same period. Researchers presenting at a press conference at the European Geosciences Union General Assembly in Vienna, Austria, suggest this may be a sign of things to come.

With climate change, wildfires are expected to be on the rise, as fire-prone regions become hotter and drier. But how did weather and climate contribute to this disastrous season? Strong winds and warm temperatures are thought to be responsible for last year’s fires in California, but it remains unclear how much climate change contributed to these conditions. Etienne Tourigny, of the Barcelona Supercomputing Centre, has been on the case.

“Would this event have been possible with or without climate change?” Tourigny asks. “It’s hard to say. What we can say is that there is a high chance that these kinds of events will be more present and more frequent in the future, especially if we see temperatures increasing as they have”

Central Portugal is already very susceptible to wildfires. It’s hot, it’s dry and it’s forested: a recipe for the perfect storm. The 2017 season was particularly tragic due to an unusual set of circumstances: a tropical cyclone passed as the Portuguese Centro Region was ablaze. The nation hoped that the hurricane would bring rain to put out the fires, but, instead, the storm passed the area by, bringing strong winds and spreading the flames.

200 thousand hectares were burned in two days. Even if this was spread throughout an entire season, it would be a very bad year. Speaking at the conference, António Ferreira, a scientific coordinator at the Research Centre for Natural Resources, Environment and Society in Coimbra, Portugal, puts it frankly: “that’s hell as it was taught in Sunday School.”

The region is also vulnerable to climate change, and an increased risk of wildfires is expected by the end of the century. New strategies are needed to prevent such losses in future. Ferreira emphasised that there is no quick fix and, to reduce the risk, policies, plans, habits and investment have to change.

Even in the high Arctic, fires present a threat. This time, it’s not a direct risk to life or infrastructure, but a threat to the environment. Nikolaos Evangeliou, from Norwegian Institute for Air Research, stated that, even in icy regions, wildfires have the capacity to alter the Earth’s climate and accelerate melting.

Thawing permafrost during the 2017 summer left Greenland’s peatlands vulnerable to wildfires and between 31 July and 21 August about 2300 hectares of peatland were burned. Seven tonnes of black carbon generated by the fires rained down on the ice sheet, making the surface darker and causing it to absorb more heat.

If the ice sheet darkens, it reduces Earth’s ability to deflect solar radiation, allowing more of the sun’s energy to warm the planet. The change in Earth’s reflectivity following last year’s wildfires was small, but it is a warning. With larger fires predicted as the climate warms, we could expect much bigger changes to the Earth’s reflectivity towards the end of the century. Such warming spells further trouble for wildfire-sensitive regions.

By Sara Mynott, EGU 2018 General Assembly Press Assistant

References

Evangeliou et al. Open Fires in Greenland: An Unusual Event and its Impact on the Albedo of the Greenland Ice Sheet. Geophysical Research Abstracts, Vol. 20, EGU2018-12383, 2018, EGU General Assembly 2018.

Leitão et al. Dealing with climate change: how to cope with wildfire threat in a climate transition region. Geophysical Research Abstracts, Vol. 20, EGU2018-16640, 2018, EGU General Assembly 2018.

Tourigny et al. An observational study of the extreme wildfire events of California in 2017: quantifying the relative importance of climate and weather. Geophysical Research Abstracts, Vol. 20, EGU2018-9545-1, 2018, EGU General Assembly 2018.

April GeoRoundUp: the best of the Earth sciences from the 2018 General Assembly

April GeoRoundUp: the best of the Earth sciences from the 2018 General Assembly

The 2018 General Assembly took place in Vienna last month, drawing more than 15,000 participants from 106 countries. This month’s GeoRoundUp will focus on some of the unique and interesting stories that came out of research presented at the Assembly.

Mystery solved

The World War II battleship Tirpitz was the largest vessel in the German navy, stationed primarily off the Norwegian coastline as a foreboding threat to Allied armies. The ship was 250 metres in length and capable of carrying around 2,500 crewmates.

Despite its massive size, the vessel’s presence often went unnoticed as it moved between fjords, masked by a chemical fog of chlorosulphuric acid released by the Nazi army.

Ultimately the ship sank and the war ended, but evidence of the toxic smog still lingers today, in the tree rings of Norway’s nearby forests.

Claudia Hartl, a dendrochronologist from the Johannes Gutenberg University in Mainz, Germany, made this discovery unexpectedly while sampling pines and birches near the Norwegian village Kåfjord. She and her research team presented their findings at the General Assembly in Vienna last month.

The German battleship Tirpitz partly covered by a smokescreen at Kaafjord. (Image Credit: Imperial War Museums )

Hartl had been examining wood cores to draw a more complete picture of past climate in the region when she noticed that some trees completely lacked rings dating to 1945,” reported Julissa Treviño in Smithsonian Magazine.

The discovery was odd since it is rare for trees to have completely absent rings in their trunks. Tree ring growth can be stunted by extreme cold or insect infestation, but neither case is severe enough to explain the missing tree rings from that time period.

“A colleague suggested it could have something to do with the Tirpitz, which was anchored the previous year at Kåfjord where it was attacked by Allied bombers,” explains Jonathan Amos from BBC News.

The researchers indeed found physical and chemical evidence of the smokescreen damage on the trees, demonstrating the long-lasting impact warfare can impart onto the environment.

 

What you might have missed

Seismicity of city life

Researchers use seismometers to record Earth’s quakes and tremors, but some seismologists have employed these instruments for a different purpose, to show how humans make cities shake. “This new field of urban seismology aims to detect the vibrations caused by road traffic, subway trains, and even cultural activities,” reports EGU General Assembly Press Assistant Tim Middleton on GeoLog.

With seismometers, Jordi Díaz and colleagues at the Institute of Earth Sciences Jaume Almera in Barcelona, Spain have been able to pick up the seismic signals of major football games and rock concerts, like footballer Lionel Messi’s winning goal against Paris Saint-Germain and Bruce Springsteen’s Barcelona show.

Seismic record captured by the seismometer during the Bruce Springsteen concert. The upper panel shows the seismogram, while the lower panel shows the spectrogram where it is possible to see the distribution of the energy between the different frequencies. (Image Credit: Jordi Díaz)

Díaz’s project first began as an outreach campaign, to teach the general public about seismometers, but now he and his colleagues are exploring other applications. For example, the data could help civil engineers with tracking traffic and monitoring how buildings withstand human-induced tremors.

Antarctica seeing more snow

Meanwhile in Antarctica, snowfall has increased by 10 percent in the last 200 years, according to new research presented at the meeting. After analysing 79 ice cores, a research team led by Liz Thomas from the British Antarctic Survey discovered that Antarctica’s increased snowfall since 1800 was equivalent to 544 trillion pounds of water, about twice the volume of the Dead Sea.

It has been predicted that snowfall increase would be a consequence of global warming, since a warmer atmosphere can hold more moisture, thus resulting in more precipitation. However, these ice core observations reveal this effect has already been happening. The new finding implies that Earth’s sea level has risen slightly less than it would have otherwise, but only by about a fifth of a milimetre. Though overall, this snowfall increase is not nearly enough to offset Earth’s increased ice loss.

Ocean’s tides create a magnetic field

Also at the Assembly, scientists presented new data collected from a team of ESA satellites known as Swarm, In particular, the satellite observations recently mapped magnetic signals induced by Earth’s ocean tides. As the planet’s tides ebb and flow, drawn by the Moon’s gravitational pull, the salty water generates electric currents. And these currents create a tiny magnetic field, around 20,000 times weaker than the global magnetic field.

Scientists involved with the Swarm project say the magnetic view provides new insight into Earth’s ocean flow and magnetic field, can improve our understanding of climate change, and help researchers build better Earth system models.

When salty ocean water flows through Earth’s magnetic field, an electric current is generated, and this in turn induces a magnetic signal. (Credit: ESA/Planetary Visions)

 

Other noteworthy stories:

 

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