GeoLog

Stratigraphy

Imaggeo on Mondays: A modern cliff hides ancient dunes

Imaggeo on Mondays: A modern cliff hides ancient dunes

Ancient sand dunes exposed off a cliff face on the shoreline of Nova Scotia at the Islands Provincial Park. The juxtaposition of the high angled strata and flat lying layers above revels the drastic change in climate in Nova Scotia’s history; from vast sand dunes to a calm lake system, and presently the western coastline of the Atlantic Ocean.

Description by Robert Wu, as it first appeared on imaggeo.egu.eu.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

Living in a new Age

Living in a new Age

If you were suddenly told you were living in a different time period, what would your immediate reaction be? Changes in the calendar – even if it’s just terminology – have proven emotive in the past. In 1752, when England shifted from the Julian to Gregorian calendars, and 11 days were cut from 1752 to catch up, there are suggestions that civil unrest ensued.

Once again, the name of the period in which we live has recently changed; the Holocene is now subdivided into three parts, and we’re now living in the Meghalayan age, according to the International Commission on Stratigraphy (ICS). While there weren’t riots in the streets this time, it has proved controversial for some researchers.

The division of time into different epochs and eras is an important part of stratigraphy. While time marches on, ignorant of the names humans give to its divisions, defining periods like the Cretaceous and Jurassic helps scientists compare results from around the world, even where the fossil and sedimentary records differ. It also draws into sharp focus the globally significant differences between each period, often including the devastating mass-extinctions that mark the boundaries of a handful of these periods.

The Holocene has been for at least a century the term favoured to describe the period in which we live, with its beginning marked by the end of the last ice age. The date at which the Holocene began has been more and more closely defined by experts over time, to the now accepted value of approximately 11,650 calendar years before present. The Holocene period encompasses the emergence of human civilisation, and represents a period of relatively warmer, somewhat stable climate in comparison with the prior ice age.

After considerable debate, however, the ICS has decided that the Holocene should be further subdivided; now, the period from 11,650 and 8,200 years before present is the Greenlandian; the Northgrippian stretches from 8,200 to 4,200 years before present, and the Meghalayan defines the time between then and the present. Why did the Holocene need to be divided up as such? If it wasn’t broken, why fix it?

The International Commission on Stratigraphy (ICS) has updated the timeline for the earth’s full geologic history, dividing the Holocene into three distinct periods. What does that mean for the Anthropocene? (Credit: International Commission on Stratigraphy)

The distinctions between an ice age and a warmer period, also known as an interglacial period, are globally significant, and a good place to start when describing how Earth’s climate has changed over the past few hundred thousand years. The swings in global temperature and ice extent are large enough that we often ignore the subtler climate changes that occur within an interglacial or glacial period. However, sediment and fossil records from more recent eras are relatively well preserved (simply because those records have had less chance to be destroyed by other geological processes), and this enables us to explore more recent periods in finer detail. Looking within the Holocene, the transition between the Greenlandian and Northgrippian is marked by a dramatic cooling of the climate, while the Northgrippian – Meghalayan by an abrupt ‘mega-drought’ and cooling that affected the nascent agricultural societies developing at that time.

By dividing the Holocene into these bite-sized chunks, the ICS has drawn attention to these changes in the earth’s geological system and provided a global context to the climatic shifts of the last ten thousand years. It also helps emphasise that climate can and does change on timescales more abrupt that glacial-interglacial periods – something we need to remember when considering the likely effects of anthropogenic climate change.

So far, so scientific. So why have the changes upset some people? Well, there’s an elephant in the stratigraphic room that looms larger now that these changes have been officially ratified. If there’s anything that has marked out the Holocene as fundamentally different from other historical ages, it’s the growth of human society. In particular, we are now at a point in history where the actions of a specific species – humans – can have global effects on the stratigraphic record.

Humans have added large quantities of carbon dioxide to the atmosphere, sown radioactive isotopes across the oceans from nuclear bomb testing, and left waste deposits in environments from the top of Mt Everest to the middle of the Pacific Ocean. Many of these impacts could leave lasting traces in the sedimentary and fossil records, leading to some scientists calling for a new period of time – the Anthropocene. And this may not fit well with the ICS changes.

I spoke with Helmut Weissert, President of the EGU Stratigraphy, Sedimentology and Palaeontology Division about these changes, and he suggested that the new changes devised by the ICS might shift the debate over the Anthropocene, at least in the short term:

I am quite worried. After the introduction of the new subdivisions I cannot see how the Holocene working group soon will vote for a further subdivision of the Holocene. The Anthropocene working group is confronted with a difficult task. I can envisage that the Anthropocene will be used as an informal term, not officially defined and introduced into the Stratigraphic Chart. I use the term regularly in my writing and in talks, everybody understands the term, I can explain how man is a geological agent. So, we may have to continue using an excellent term which is not yet properly defined, but most people do not care about the definition.

The Anthropocene is certainly an effective term to draw the attention of the wider public to the impact of society on global geological cycles. But from a stratigraphic perspective, it offers a number of challenges. Where and when, for example, should the beginning of the period be set? Changes in geological periods require specific chemical changes that can be identified globally and an internationally agreed upon reference point – a physical location – that defines the base of the section. There are many potential examples that could be chosen to define the beginning of human interference in the natural system; ice cores showing the uptick in carbon dioxide at the industrial revolution, or ocean sediments attesting to nuclear bomb tests in the 1950s. But the choice of which section to pick is fraught.

Each stratigraphic division needs a reference point that defines the split between the prior time period and the one in question. Here, a ‘golden spike’ defines the base of the Ediacaran period (635 million years ago) in the Flinders Ranges of South Australia. (Credit: Bahudhara via Wikimedia Commons)

Moreover, preservation is a crucial part of stratigraphy; how much of human impact will in fact be preserved, especially after further anthropogenic changes? What if we clean up the environment? What if we dredge the ocean floor for rare metals, and, in doing so, extirpate the signal of the 1950s nuclear bomb tests? What if we melt the ice caps that record the incipient CO2 increases from the industrial revolution? Sure, these changes may be recorded elsewhere, but how can we be sure a reference stratigraphic section will remain intact?

And this brings us to a perhaps more philosophical point: what if the human impact on the natural system we see today is only a fraction of what is to come? Any Anthropocene we define now would be based only upon the impact to date, but future changes may make these seem small in comparison. What would come after the Anthropocene? The question echoes that of 20th century philosophers, asking what comes after Post-Modernism? Perhaps instead of stratigraphy, we should look to written history and recorded data to better contextualise our impact.

Whether we end up defining our current era as the Meghalayan, the Anthropocene, or something else, it seems clear that the debate has drawn increased attention to the short-term climate changes – and in particular those driven by human intervention. A better public appreciation of our role within the natural system is a vital step in limiting damaging future climate change.

by Robert Emberson

Robert Emberson is a Postdoctoral Fellow at NASA Goddard Space Flight Center, and a science writer when possible. He can be contacted either on Twitter (@RobertEmberson) or via his website (www.robertemberson.com)

July GeoRoundUp: the best of the Earth sciences from around the web

July GeoRoundUp: the best of the Earth sciences from around the web

Drawing inspiration from popular stories on our social media channels, as well as unique and quirky research news, this monthly column aims to bring you the best of the Earth and planetary sciences from around the web.

Major stories  

Signs of water 55 million kilometres away

Last week scientists announced that they have found signs of existing water on Mars, offering new hope to the possibility of uncovering life on the Red Planet’s subsurface.  

Radar observations made by the European Space Agency’s Mars Express satellite, suggest that a liquid lake is buried 1.5 kilometres beneath an ice cap situated near the south pole of Mars. Scientists think that this body of water is likely a few metres deep and 20 kilometres across, “nearly three times larger than the island of Manhattan,” reported Scientific American.

A schematic of how scientists used radar to find what they interpret to be liquid water beneath the surface of Mars. (Credit: ESA)

For the last 12 years the Mars Express satellite has been taking measurements of Mars by sending beams of radar pulses into the planet’s immediate interior. As these waves bounce back, the brightness of the reflection gives information on the material lying beneath Mars’ surface.

The researchers involved came across this discovery while analysing three years worth of data collected by the spacecraft.

“The bluer the colors, the brighter the radar reflection from the material it bounced off. The blue triangle outlined in black in the middle is the purported lake,” reported Science News.

Previous observations, made by NASA’s Curiosity rover for example, have found lake beds on the planet’s exterior, signifying that water may have flowed on Mars in the past. However, if this new finding is confirmed, it would be the first discovery of an existing stable body of water, one of the conditions believed to be necessary for life to thrive.

Context map: NASA/Viking; THEMIS background: NASA/JPL-Caltech/Arizona State University; MARSIS data: ESA/NASA/JPL/ASI/Univ. Rome; R. Orosei et al 2018 (distributed via ESA)

“We are not closer to actually detecting life,” said Manish Patel from the Open University to BBC News, “but what this finding does is give us the location of where to look on Mars. It is like a treasure map – except in this case, there will be lots of ‘X’s marking the spots.”

In their study, published in Science last week, the team remarked, “there is no reason to conclude that the presence of subsurface water on Mars is limited to a single location.”

Northern hemisphere feels the heat

In other news, the two words best describing the northern hemisphere this summer could very well “hot” and “dry,” as a series of heat waves have taken hold of several regions across Europe, Asia, North America and northern Africa. Many countries this month, including Japan, Algeria and Canada, have even experienced record-breaking temperatures.

A look at how this year’s heatwave has changed the colour of our vegetation in just one month (Credit: ESA

For some places, above average temperatures and dry conditions have helped fuel devastating wildfires. More than 50 wildfires have swept through Scandinavian forests this summer, many well within the Arctic Circle, causing Sweden to request emergency aid from nearby countries.

Smoke rises from a wildfire in Enskogen. (Credit: Swedish Environmental Protection Agency/Maja Suslin)

A major wildfire also ignited near Athens, Greece this month, resulting in more than 85 death, with dozens still missing. While Greek officials claim that there are “serious indications” that the flames were brought upon by arson, they also note that the region’s climate conditions were extreme.

To many scientists, this onslaught of hot and dry conditions is a taste of what may soon become the norm.  Of course, these conditions (in Europe, for example) are partly due to weather. “The jet stream – the west-to-east winds that play a big role in determining Europe’s weather – has been further north than usual for about two months,” reports the Guardian, leading to sweltering conditions in the UK and much of Europe, while leaving Iceland cool and stormy.  

However, scientists say that heatwaves in the northern hemisphere are very much linked to global warming. “There’s no question human influence on climate is playing a huge role in this heatwave,” said Myles Allen, a climate scientist at the University of Oxford, to the Guardian in the same article.

A recent assessment on the ongoing heat wave in Europe reports that these conditions are more likely to occur due to climate change. “The findings suggest that rising global temperatures have increased the likelihood of such hot temperatures by five times in Denmark, three times in the Netherlands and two times in Ireland,” said Carbon Brief.

What you might have missed

Geologists have given a name to Earth’s most recent chapter: Meghalayan Age. The announcement was made earlier this month when the International Union of Geological Sciences updated the International Chronostratigraphic Chart, which classifies Earth’s geologic time scale. The new update has divided the Holocene Epoch (the current time series which began 11,700 years ago, when the Earth was exiting its last ice age) into three stages: the Greenlandian, the Northgrippian, and then Meghalayan.

The Meghalayan Age represents the time between now and 4,200 years ago, when a mega-drought led to the collapse of many civilisations across the world. The middle phase, Northgrippian (from 8,300 years ago to 4,200 years ago), is marked by an sudden cooling event brought on by massive glacial melt in Canada that affected ocean currents. Finally the oldest phase, Greenlandian, (from 11,700 years ago to 8,300 years ago) is marked by the end of the last ice age.

The recent update has created some unrest in the geosciences community. “There is still an active debate about assigning a new geologic slice of time to reflect specifically the influence of humans on the planet,” reported BBC News. Some scientists say that the new divisions conflict with the current work being done on proposing a new epoch classification, famously called the ‘Anthropocene,’ which would be marked by the beginning on significant human impact on Earth’s geology and ecosystems.

Links we liked

The EGU story

This month we released not one but two press releases from research published in our open access journals. The findings from both studies have important societal implications. Take a look at them below.

New study: oxygen loss in the coastal Baltic Sea is “unprecedentedly severe”

The Baltic Sea is home to some of the world’s largest dead zones, areas of oxygen-starved waters where most marine animals can’t survive. But while parts of this sea have long suffered from low oxygen levels, a new study by a team in Finland and Germany shows that oxygen loss in coastal areas over the past century is unprecedented in the last 1500 years. The research was published in the European Geosciences Union journal Biogeosciences.

New study puts a figure on sea-level rise following Antarctic ice shelves’ collapse

An international team of scientists has shown how much sea level would rise if Larsen C and George VI, two Antarctic ice shelves at risk of collapse, were to break up. While Larsen C has received much attention due to the break-away of a trillion-tonne iceberg from it last summer, its collapse would contribute only a few millimetres to sea-level rise. The break-up of the smaller George VI Ice Shelf would have a much larger impact. The research was published in the European Geosciences Union journal The Cryosphere.

And don’t forget! To stay abreast of all the EGU’s events and activities, from highlighting papers published in our open access journals to providing news relating to EGU’s scientific divisions and meetings, including the General Assembly, subscribe to receive our monthly newsletter.

Geoscience hot topics – Part I: The Earth’s past and its origin

Geoscience hot topics – Part I: The Earth’s past and its origin

What are the most interesting, cutting-edge and compelling research topics within the scientific areas represented in the EGU divisions? Ground-breaking and innovative research features yearly at our annual General Assembly, but what are the overarching ideas and big research questions that still remain unanswered? We spoke to some of our division presidents and canvased their thoughts on what the current Earth, ocean and planetary hot topics will be.

There are too many to fit in a single post so we’ve brought some of them together in a series of posts which will tackle three main areas: the Earth’s past and its origin, the Earth as it is now and what its future looks like, while the final post of the series will explore where our understanding of the Earth and its structure is still lacking. We’d love to know what the opinions of the readers of GeoLog are on this topic too, so we welcome and encourage lively discussion in the comment section!

 

The Earth’s past and its origin

Rephrasing the famous sentence by James Hutton, i.e. the present is the key to the past, we can even say that the past is the key to the future – a better understanding of past Earth processes can help understand why and how our planet evolved to have oceans, an atmosphere, a planetary magnetic field as well as the ability to sustain life. Not only that, a greater understanding of the Earth’s past can aid in finding solutions to present day problems. A strong interdisciplinary research effort is required to delve into the Earth’s past and that makes it one of the most important geoscience hot topics, albeit very broad.

Life on Earth and the physical environment

Zircons in rocks from Jack Hills in Western Australia provide evidence of oceans 4.4 b.y. ago and of conditions that may have haboured life. The remarkable thing is that these rocks are 300 million years older than the 3.8 billion year old rocks from Greenland, which were thought to hold the oldest evidence for life on Earth, until now.

Image by Robert Simmon, based on data from the University of Maryland’s Global Land Cover Facility

Jack Hills, Western Australia. Image by Robert Simmon, based on data from the University of Maryland’s Global Land Cover Facility

These findings are no doubt very exciting, but they also go hand in hand with gaining a greater understanding about the physical environment in which these early life forms evolved. According to Helmut Weissert, President of the Stratigraphy, Sedimentology and Palaeontology Division (SSP), understanding the co-evolution of life and the physical environment in Earth’s history is one of the biggest challenges for current and future scientists. Understanding past changes of the System Earth will facilitate the evaluation of man’s role as a major geological agent affecting global material and geochemical cycles in the Anthropocene.

The work of scientists in the SSP fields on understanding how the evolution of life was affected by major climatic perturbations is particularly timely, given the ongoing debate as to whether the presence of humans on Earth is potentially driving a sixth mass extinction event. Not only that, a big research question still unanswered is how did catastrophic events during the Earth’s history also affect evolutionary rates?

Developing new models and tools which might aid investigation in these areas is at the forefront of challenges to come, along with a greater interaction between related disciplines, for instance (but of course, not limited to!) the geosciences and genetics.

A changing inner Earth

The Earth’s magnetic field is one of ingredients for the presence of life on Earth, because it screens most of the cosmic rays that otherwise would penetrate in major quantities into the atmosphere and reach the surface, being dangerous for human health.

“A recent discovery is that the absence of magnetic field would cause serious damages not only to humans through a significant increase of cancer cases, but also to plants”, say Angelo De Santis, President of the Earth Magnetism and Rock Physics Division (EMRP), “implying that geomagnetic field reversals characterised by times with very low intensity of the field, would have serious implications for life on the planet”.

Another way to understand this aspect would be to have a look at the past. One of the (many) tools which can be used to understand what our planet might have looked like in its infancy is palaeomagnetism. This is especially true when it comes to one of the biggest conundrums of the Precambrian: when did plate tectonics, as we understand them now, start?

That there was perhaps some form of plate motions in the Earth’s early life is likely, but exactly what the style of those plate motions were during the Precambrian is still highly debated. Palaeomagnetic directions measured over time are used to estimate lateral plate motions associated with modern day style plate tectonics involving subduction. If similar plate motions can be identified in rocks younger than 500Ma then they might support lateral plate motions early in the Earth’s history. This, says Angelo De Santis, is one of the most exciting areas of research within Earth magnetism.

 Earth Magnetic Field Declination from 1590 to 1990 by U.S. Geological Survey (USGS). Licensed under Public Domain via Wikimedia Commons . Click on the image to see how the field changes over time.

Earth Magnetic Field Declination from 1590 to 1990 by U.S. Geological Survey (USGS). Licensed under Public Domain via Wikimedia Commons . Click on the image to see how the field changes over time.

Not only that, studying the strength of the geomagnetic field (which is generated in the liquid outer core by a process known as the geodynamo) and how it changes over different time scales can give us information about the early inner structure of the planet. For instance, news of a new date for the age of the formation of the inner core, after researches identified the sharpest increase in the strength of the Earth’s magnetic field, hit the headlines recently. The findings imply that maybe some of the views Earth scientists hold about the core of the Earth might need to be revised!

Which leads us onto secular variation – the study of how the geomagnetic field changes, not only in strength but also in direction – because if the early core is different to how it was previously thought, is the understanding of secular variation also affected? The implications are far reaching, but a highlight, according to Angelo De Santis, has to be how the findings might affect how periods of large change (more commonly known as geomagnetic reversals) are understood. Therefore, it is key that the evolution of the geodynamo is better understood, so that scientists might be able to assess the possibility of an imminent excursion (a large change of the field, but not a permanent flip of the direction) or reversal.

From the inner Earth to the surface

If studying the inner depths of the Earth in the past might give us clues about the present and future of the planet’s core, so to on and above the surface the past can be the key to the future.

Geological time spiral" by United States Geological Survey - Graham, Joseph, Newman, William, and Stacy, John, 2008, The geologic time spiral—A path to the past (ver. 1.1): U.S. Geological Survey General Information Product 58, poster, 1 sheet. Available online at http://pubs.usgs.gov/gip/2008/58/. Licensed under Public Domain via Commons.

Geological time spiral by United States Geological Survey – Graham, Joseph, Newman, William, and Stacy, John, 2008, The geologic time spiral—A path to the past (ver. 1.1): U.S. Geological Survey General Information Product 58, poster, 1 sheet. Available online at http://pubs.usgs.gov/gip/2008/58/. Licensed under Public Domain via Commons.

Present day climate change is a given, but predictions of how the face of the Earth might change as a result remain difficult to make while, at the same time, its consequences are not yet fully understood. Studying the climate of the past and how the biosphere, oceans and the Earth’s surface (including erosion and weathering processes), responded to abrupt and potentially damaging changes in Earth’s past climate provides a starting point to make forecasts about the future.

“A better time resolution of geological archives means we are able to further test present day climate, weathering and ocean models,” says SSP President Helmut Weissert.

And so, not only does the past tell us where we come from and how the Earth became the only planet in our Solar System capable of sustain complex forms of life, a better understanding of its origins and past behaviour might just help us improve the future too.

Next time, in the Geosciences hot topics short series, we’ll be looking at our understanding of the Earth as we know it now and how we might be able to adapt to the future. The question of how we develop the needs for an ever growing population in a way that is sustainable opens up exciting research avenues in the EMRP and SSP Divisions, as well as the Energy, Resources and the Environment (ERE), Seismology (SM) and Earth and Space Science Informatics (ESSI) Divisions.