GeoLog

Tectonics and Structural Geology

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.

How to make a planet habitable

How to make a planet habitable

Exoplanets without plate tectonics could harbour life, contrary to previous belief

For a planet to be habitable, it needs a stable climate. On Earth, the movement of tectonic plates ensures old crust is recycled and new crust is created and weathered. This cycling of rock consequently overturns the planet’s carbon, which keeps the climate in check.

While we have plate tectonics on Earth, many other rocky planets have what is called a ‘stagnant lid’. In this system, there is one solid plate wrapped around the planet, and the mantle circulates beneath it. The same recycling processes found on Earth don’t occur in these stagnant lid planets, preventing regulation of the carbon cycle and generating an inhospitable climate, or so scientists thought.

It is often claimed that plate tectonics is a requirement for a habitable climate, but research presented at the EGU General Assembly in Vienna suggests that some of these stagnant lid planets may be habitable after all.

Volcanic activity on stagnant lid planets could provide enough fresh rock for weathering to operate like it does on Earth, suggests Bradford Foley, a geologist from Pennsylvania State University in University Park, Pennsylvania. This means that simply burying the crust by lava flows could recycle enough CO2 to regulate the climate.

In their early history, the rocky surfaces of stagnant lid planets release gases that form an atmosphere. These young planets are also peppered with volcanoes that produce fresh, weatherable rock. Combined, these processes create a carbon cycle and, if the conditions are right, they can maintain a stable climate for long periods of time.

By modelling processes on stagnant lid planets that are similar in size to Earth, Foley was able to work out what conditions would create a habitable climate. The balance lies in striking the right amount of degassing, the process in which volcanoes release gas into the atmosphere. Not enough would lead to full surface glaciation, as too thin an atmosphere would make the planet extremely cold. On the other hand, too much degassing would generate a thick, CO2-rich atmosphere, leading to an incredibly hot environment.

There are two planetary budgets to take into account: carbon and heat. “We found a sweet spot, around Earth’s total amount of carbon to an order of magnitude less than that,” says Foley. That’s about 10 times less carbon than there is in Earth’s atmosphere, mantle and crust combined. Much lower, and there’s not enough of an atmosphere to keep the planet warm.

The other important consideration is the planet’s heat budget. As radioactive elements decay, they produce heat, and the more of these heat-producing elements a planet has, the bigger its heat budget. If a stagnant lid planet has fewer heat-producing elements than Earth, volcanic activity dies off pretty quickly and the planet cools off. “Without volcanism, the planet would most likely freeze over,” Foley adds. The more heat-producing elements there are, the longer volcanism can last. This means that, potentially, habitable climates could last longer too.

“Planets with two to two and a half times the heat budget for Earth can have potentially habitable climates lasting for three to four billion years, plenty enough time for developing life,” Foley explains.

According to Foley, the model could be used to guide future exoplanet missions. If we know how old a planet is and have information on its heat budget we can work out its chances of being habitable, says Foley. Both of these can be worked out using observations from Earth and could be used to create new targets for planetary exploration.

Lena Noack, a planetary scientist and Junior Professor at Free University Berlin who was not involved in the study, shared her thoughts on the research: “it shows, even though plate tectonics would typically always be considered as a better indicator for habitability, stagnant lid planets do not need to be ruled out. A good example is Mars; it was locally habitable early on in its history, but if it would just be a little bit larger, of Earth size as in Foley’s study, it is not difficult to imagine that it would be quite a habitable place at present day.”

By Sara Mynott

References: 

Foley,  B. Climate Stability and Habitability of Earth-like Stagnant Lid Planets. EGU General Assembly. 2018. 

Foley, B. and Smye, A. Carbon cycling and habitability of Earth-size stagnant lid planetsarXiv:1712.03614v1. 2017.

Imaggeo on Mondays: The best of imaggeo in 2017

Imaggeo on Mondays: The best of imaggeo in 2017

Imaggeo, our open access image repository, is packed with beautiful images showcasing the best of the Earth, space and planetary sciences. Throughout the year we use the photographs submitted to the repository to illustrate our social media and blog posts.

For the past few years we’ve celebrated the end of the year by rounding-up some of the best Imaggeo images. But it’s no easy task to pick which of the featured images are the best! Instead, we turned the job over to you!  We compiled a Facebook album which included all the images we’ve used  as header images across our social media channels and on Imaggeo on Mondays blog post in 2017 an asked you to vote for your favourites.

Today’s blog post rounds-up the best 12 images of Imaggeo in 2017, as chosen by you, our readers.

Of course, these are only a few of the very special images we highlighted in 2017, but take a look at our image repository, Imaggeo, for many other spectacular geo-themed pictures, including the winning images of the 2017 Photo Contest. The competition will be running again this year, so if you’ve got a flare for photography or have managed to capture a unique field work moment, consider uploading your images to Imaggeo and entering the 2018 Photo Contest.

Alpine massifs above low level haze . Credit: Hans Volkert (distributed via imaggeo.egu.eu).

The forward scattering of sunlight, which is caused by a large number of aerosol particles (moist haze) in Alpine valleys, gives the mountain massifs a rather plastic appearance. The hazy area in the foreground lies above the Koenigsee lake; behind it the Watzmann, Hochkalter, Loferer Steinberge and Wilder Kaiser massifs loom up behind one other to the right of the centre line. Behind them is the wide Inn valley, which extends right across the picture.

A lava layer cake flowing . Credit: Timothée Duguet (distributed via imaggeo.egu.eu)

Check out a post from back in May to discover how layers of alternating black lavas and red soils built up to form a giant ‘mille feuilles’ cake at Hengifoss, Iceland’s third-highest waterfall.

Sediment makes the colour . Credit: Eva P.S. Eibl (distributed via imaggeo.egu.eu)

Earth is spectacularly beautiful, especially when seen from a bird’s eye view. This image, of a sweeping pattern made by a river in Iceland is testimony to it. Follow the link to learn more about river Leirá which drains sediment-loaded glacial water from the Myrdalsjökull glacier in Iceland.

Movement of ancient sand . Credit: Elizaveta Kovaleva (distributed via imaggeo.egu.eu).

Snippets of our planet’s ancient past are frozen in rocks around the world. By studying the information locked in formations across the globe, geoscientist unpick the history of Earth. The layers in one of the winning images of the 2017 photo contest may seem abstract to the untrained eye, but Elizaveta Kovaleva (a researcher at the University of the Free State in South Africa) describes how they reveal the secrets of ancient winds and past deserts in a blog post we published in November.

View of the Tuva River and central mountain range
. Credit: Lisa-Marie Shillito (distributed via imaggeo.egu.eu).

Initially, this photo may seem like any other tropical paradise: lush forests line a meandering river, but there is much more to the forests in the foreground than first meets the eye.

On the way back from Antarctica. Credit: Baptiste Gombert (distributed via imaggeo.egu.eu).

Our December 2017 header image – On the way back from Antarctica, by Baptiste Gombert – celebrated #AntarcticaDay.

Angular unconformity. Credit: André Cortesão (distributed via imaggeo.egu.eu).

It is not unusual to observe abrupt contacts between two, seemingly, contiguous rock layers, such as the one seen above. This type of contact is called an unconformity and marks two very distinct times periods, where the rocks formed under very different conditions.

Find a new way . Credit: Stefan Winkler (distributed via imaggeo.egu.eu)

Stephan Winkler’s 2017 Imaggeo Photo Contest finalist photo showcases an unusual weather phenomenon…find out more about this process in the post from last year.

On the way back from Antarctica. Credit: Alicia Correa Barahona (distributed via imaggeo.egu.eu).

August’s social media header image showcases how, in the altiplano of Bolivia, Andean ecosystems, life and the hydrological cycle come together.

Icelandic valley created during a volcanic eruption. Credit: Manuel Queisser (distributed via imaggeo.egu.eu).

The image shows a valley in the highland of Iceland carved out during a volcanic eruption with lava coming from the area visible in the upper right corner. The landscape is playing with the viewers sense of relation as there is no reference. The valley is approximately 1 km wide. The lower cascade of the water fall is ca. 30 m high. A person (ca. 3 pixels wide) is located near the base of the water fall about 50 m away. It was our October header image.

Despite being one of the driest regions on Earth, the Atacama desert is no stranger to catastrophic flood events. This post highlights how the sands, clays and muds left behind once the flood waters recede can hold the key to understanding this natural hazard.

The heart of the Canadian Rocky Mountains. Credit: Jennifer Ziesch (distributed via imaggeo.egu.eu).

“I saw one of the most beautiful place on earth: The glacially-fed Moraine Lake in the Banff National Park, Canada. The lake is situated in the Valley of the Ten Peaks. The beautiful blue colour is due to the mix of glacier water and rock flour,” says Jennifer, who took the photograph of this tranquil setting.

Symbiosis of fire, ice and water . Credit: Michael Grund (distributed via imaggeo.egu.eu)

This mesmerising photograph is another of the fabulous finalists (and winner) of the 2017 imaggeo photo contest. The picture, which you can learn more about in this blog post, was taken at Storforsen, an impressive rapid in the Pite River in northern Sweden, located close to the site of a temporary seismological recording station which is part of the international ScanArray project. The project focuses on mapping the crustal and mantle structure below Scandinavia using a dense temporary deployment of broadband seismometers.

f you pre-register for the 2018 General Assembly (Vienna, 08 – 13 April), you can take part in our annual photo competition! From 15 January up until 15 February, every participant pre-registered for the General Assembly can submit up three original photos and one moving image related to the Earth, planetary, and space sciences in competition for free registration to next year’s General Assembly!  These can include fantastic field photos, a stunning shot of your favourite thin section, what you’ve captured out on holiday or under the electron microscope – if it’s geoscientific, it fits the bill. Find out more about how to take part at http://imaggeo.egu.eu/photo-contest/information/.

MinCup: Elevating humble minerals to new heights

MinCup: Elevating humble minerals to new heights

Throughout October and November, the world of (Earth science) Twitter was taken by storm: Day after day, Eddie Dempsey (a lecturer at the University of Hull, and @Tectonictweets for those of you more familair with his Twitter handle) pitted minerals against each other, in a knock out style popular contest. The aim? To see which mineral would eventually be crowned the best of 2017.

Who knew fiery (but good natured) rows could explode among colleagues who felt, strongly, that magnetite is far superior to quartz or plagioclase? The Mineral Cup hashtag (#MinCup) was trending, it was in everyone’s mouth. Who would you vote for today?

What started as a little fun, became a true example of great science communication and how to bring a community of researchers, scattered across the globe, together.

And then Hazel Gibson (former EGU Press Assistant, @iamhazelgibson) came along. She was an active participant in the competition, but also contributed beautiful sketches of every mineral featured, and shared them for all to see by tagging them with the #MinCup hashtag. We all know that a picture is worth more than a thousand words, so when Hazel’s hand drawn sketches where paired with an already rocking contest, it’s impact and reach was truly cemented.

Between them, Eddie and Hazel had managed to elevate the humble mineral to new heights.

Why do minerals matter?

Minerals are hugely underrated. They are often upstaged by the heavy-weights of the geosciences: volcanoes, earthquakes, hurricanes, fossils and melting glaciers (to name but a few).

But they shouldn’t be.

Minerals are the building blocks of all rocks, which in turn, are the foundation of all geology.

Whether you study the processes which govern how rivers form, or ancient magnetic fields, or fossils, chances are your work will, at some stage, involve looking at, studying, or at the very least understanding (some) minerals. Mineralogy 101 (or whatever it’s precise name was at your university) is a rite of passage for any aspiring Earth scientist. I still remember hours spent painstakingly looking down a microscope, drawing and annotating sketches trying to decipher the secrets of the Earth’s ancient past, locked in minerals.

And that’s just the beginning.

Minerals are of huge economic and, therefore societal importance, too. Many minerals are vital ingredients in house-hold products and contribute to the manufacturing processes of many others. Yet, they fail to make headlines and their true significance, often, goes unnoticed.

So, in hopes to further highlight the relevance and importance of minerals, I’ve picked a few of the #MinCup minerals and explained why they (should) matter (to you).

Gypsum

Gypsum will form in lagoons, where ocean waters are high in calcium and sulfate content, and where the water evaporates slowly overtime. In rocks, it is associated with sedimentary beds which can be mined to extract the mineral, but it can also be produced by evaporating water with the right chemical composition.

Gypsum has been used in construction and decoration (in the form of alabaster) since 9000 B.C.  Today, it has a wide variety of common uses. Did you know that many fruit juice companies use gypsum to aid the extraction of the liquid? It is also used in bread and dough mixes as a raising agent. And it’s uses aren’t limited to just the food and drink industry. It is also commonly used as a modelling material for tooth restorations and helps keeps us safe when added to plastic products where it acts as a fire retardant.

Magnetite

Geologically speaking, magnetite holds the clues to understand the Earth’s ancient magnetic field. Credit: Hazel Gibson

Typically, greyish black or black, magnetite is an important iron ore mineral. It occurs in many igneous and volcanic rocks and is the most magnetic of all minerals. For it to form, magma has to cool, slowly, so that the minerals can form and settle out of the magma.

Due to its magnetic nature, it has fascinated human-kind for centuries: it paved the way for the invention of the modern compass.  The iron content in magnetite is higher than its more common cousin haematite, making it very sought after. Iron ore is the source of steel, which is used universally throughout modern infrastructure.

Geologically speaking, magnetite holds the clues to understand the Earth’s ancient magnetic field. As magnetite-bearing rocks form, the magnetite within them aligns with the Earth’s magnetic field. Since this rock magnetism does not change after the rock forms, it provides a record of what the Earth’s magnetic field was like at the time the rock formed.

Diamond

Arguably, one of the most well-known of the minerals, diamond is unique, not only for its beauty and the high prices it reaches, but also for its properties. Not only is it the hardest known mineral, it is also a great conductor of heat and has the highest refractive index of any mineral.

Though mostly sought after by the jewellery industry, only 20% of all diamonds are suitable for use as a gem. Due to it’s hardness, diamond is mined for use in industrial processes, to be used as an abrasive and in diamond tipped saws and drills. Its optical properties mean it is used in electronics and optics; while it’s conductive properties mean it is often used as an insulator too.

Diamond: perhaps the most sought after mineral of them all? Credit: Hazel Gibson

Olivine

Last, but absolutely not least, let’s talk about Olivine – the winner of #MinCup 2017.

Olivine is a pretty, commonly green mineral. Because it forms at very high temperatures, it is one of the first minerals to take shape as magma cools, and given enough time, can form specimens which are easily seen with the naked eye. Changes in the behaviour of seismic waves as they traverse the Earth indicate that Olivine is an important component of the Earth’s inner layer – the Mantle.

It’s a relatively hard mineral, but overall hasn’t got highly sought-after properties and, as result, has been used rather sparingly in industrial processes. In the past it has been used in blast furnaces to remove impurities from steel and to form a slag, as well as a refractory material, but both those uses are in decline as cheaper materials come to the market.

Perhaps better known is its gemstone counterpart: peridot, a magnesium rich form of Olivine. It has been coveted for centuries, with some arguing that Cleopatra’s famous ‘emeralds’, where in fact peridote. Until the mid-90s the US was the major exporter of the gem stones, but deposits in Pakistan and China now challenge the claim.

So, do you think Olivine was the rightful winner of #MinCup 2017? With a new edition of the popular contest set to return in 2018, perhaps it’s time to shout about the properties and uses of your favourite mineral from the roof tops? Not only might it ensure it is crowned winner next year, but you’ll also be contributing to making the value of minerals known to the wider public. Heck! If you’d like to tell us all about the mineral you think should be the next champion, why not submit a guest post to GeoLog?

In the meantime, if you haven’t already got your hands on one, Hazel tells me there are a few of her charity #MinCup 2017 calendars up for grabs, so make sure to secure your copy – and contribute to a good cause at the same time.

By Laura Roberts Artal, EGU Communications Officer