Mass production of tar may have helped Viking expansion

Did the use of tar help Vikings create waterproof ships and therefore travel long distances and conquer faraway lands? The technology for the mass production of tar had not been supported by hard evidence, until recently, when excavations in Sweden revealed large tar-producing structures which were clearly not meant for domestic use. A new study has presented a theory connecting tar mass production with the success of Viking campaigns.

Mass production of tar may have helped Viking expansion
Tenth-century tar pit from the Gnezdovo site, Smolensk region [Credit:; A.A. Fetisov,
State Museum of Oriental Art/Antiquity]

The discovery was made by Andreas Hennius, of Uppsala University, and was published in Antiquity. Excavations in Eastern Sweden have revealed funnel-shaped pits, which have been identified as structures for producing tar. In the 8th century AD, tar production increased into large-scale and was relocated to outland forests.

Mass production of tar may have helped Viking expansion
Schematic section of a tar kiln with a tar outlet pipe in the bottom, used in Scandinavia in historical times
(letters I and J are not used) [Credit: Bergström 1941: part II, p. 57/Antiquity]

Since tar was made in pits filled with pine wood, covered with turf and set on fire, the forests provided the raw material needed. They would produce up to 300 litres in a single production cycle, clear evidence of mass-production, according to Hennius. Of course, small domestic tar kilns had been found in Sweden earlier, but the discovery of the larger tar pits is evidence of a large-scale production.

Mass production of tar may have helped Viking expansion
Funnel-shaped feature used for tar production in the Roman Iron Age and a schematic
reconstruction drawing [Credit: Kurzweil & Todtenhaupt 1998/Antiquity]

The exploitation of tar pits in Scandinavia seems to have increased dramatically at the same time when Vikings started raiding other parts of Europe and maritime activities led to higher demand for the substance. Intensive tar manufacturing also indicates that new structures were created for the production, labour, forest management and transportation of the substance, affecting Scandinavian society and its structure.

Mass production of tar may have helped Viking expansion
Summarised calibration diagram from 38 tar-production pits excavated at settlement sites (above), and the seven
dated tar-production pits from the forests below [Credi: Reimer et al. 2004; Bronk Ramsey 2009;
unpublished compilation by Svensson-Hennius 2017/Antiquity]

Hennius’ theory might also assist researchers identify the reasons why Vikings expanded to such an extent, since more waterproof ships means longer journeys.

Source: Archaeology & Arts [November 07, 2018]

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ESA’s gravity-mapper reveals relics of ancient continents under Antarctic ice

ESA – GOCE Mission logo.

7 November 2018

It was five years ago this month that ESA’s GOCE gravity-mapping satellite finally gave way to gravity, but its results are still yielding buried treasure – giving a new view of the remnants of lost continents hidden deep under the ice sheet of Antarctica.

A research team from Germany’s Kiel University and the British Antarctic Survey published their latest GOCE-based findings this week in the journal Scientific Reports.

GOCE reveals Antarctic tectonics

Dubbed ‘the Formula one of space’, the GOCE (Gravity field and Ocean Circulation Explorer) mission orbited Earth for more than four years, from March 2009 to November 2013. This sleek, finned satellite with no moving parts was designed around a single goal: to measure the pull of Earth’s gravity more precisely than any mission before.

GOCE flew at an altitude of just 255 km, more than 500 km nearer than a typical Earth observation satellite, to maximise its sensitivity to gravity.

In its last year in orbit, with its supply of xenon propellant holding out well, GOCE was manoeuvred down still lower, to just 225 km altitude, for even more accurate gravity measurements. The propellant keeping it resistant to air drag was finally spent in October 2013, and it reentered the atmosphere three weeks later.

GOCE’s main output was a high-fidelity global gravity map or ‘geoid’, but the mission also charted localised gravity gradients – measurements of how rapidly the acceleration of gravity changes – across all directions of motion, down to a resolution of 80 km.

GOCE: orbiting on the edge

The team from Kiel University and BAS has converted this patchwork of 3D gravity measurements into curvature-based ‘shape indexes’ across the different regions of our planet, analogous to contours on a map.

The study’s lead author Prof Jörg Ebbing from Kiel University comments, “The satellite gravity data can be combined with seismological data to produce more consistent images of the crust and upper mantle in 3D, which is crucial to understand how plate tectonics and deep mantle dynamics interact.”

In combination with existing seismological data, these gravity gradients show high sensitivity to known features of Earth’s ‘lithosphere’, the solid crust and that section of the molten mantle beneath it.

GOCE’s global tectonic map

These features include dense rocky zones called cratons – remnants of ancient continents found at the heart of modern continental plates – highly folded ‘orogen’ regions associated with mountain ranges and the thinner crust of ocean beds.

The new window into the deep subsurface offered by this data offers novel insights into the structure of all Earth’s continents, but especially Antarctica. With more than 98% of its surface covered by ice with an average thickness of 2 km, the southern continent largely remains a blank spot on current geological maps.

“These gravity images are revolutionising our ability to study the least understood continent on Earth, Antarctica,” says co-author Fausto Ferraccioli, Science Leader of Geology and Geophysics at BAS.

“In East Antarctica we see an exciting mosaic of geological features that reveal fundamental similarities and differences between the crust beneath Antarctica and other continents it was joined to until 160 million years ago.”

GOCE map of Antarctica on bedrock topography

The gravity gradient findings show West Antarctica has a thinner crust and lithosphere compared to that of East Antarctica, which is made up of a mosaic of old cratons separated by younger orogens, revealing a family likeness to Australia and India.

These findings are of more than purely historic geological interest. They give clues to how Antarctica’s continental structure is influencing the behavior of ice sheets and how rapidly Antarctica regions will rebound in response to melting ice.

ESA’s GOCE mission scientist Roger Haagmans adds, “It is exciting to see that direct use of the gravity gradients, which were measured for the first time ever with GOCE, leads to a fresh independent look inside Earth – even below a thick sheet of ice.

“It also provides context of how continents were possibly connected in the past before they drifted apart owing to plate motion.”

Related links:

Scientific Reports: Latest GOCE-based findings: https://www.nature.com/articles/s41598-018-34733-9

GOCE+Antarctica: https://www.bas.ac.uk/project/goceantarctica

Access GOCE data: http://earth.esa.int/GOCE/

GOCE: http://www.esa.int/Our_Activities/Observing_the_Earth/GOCE

ESA EO Science for Society: https://eo4society.esa.int/

Kiel University: https://www.uni-kiel.de/en/

British Antarctic Survey: https://www.bas.ac.uk/

Images, Video, Text, Credits: ESA/Kiel University/P. Haas/BAS.

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Dry conditions may have helped a new type of plant gain a foothold on Earth

In the dramatically changing conditions of ancient Earth, organisms had to evolve new strategies to keep up. From the mid-Oligocene, roughly 30 million years ago, to the mid-to-late Miocene, about 5 million years ago, carbon dioxide concentrations in the atmosphere fell by a roughly a third. This same period saw the emergence of a new form of photosynthesis in a subset of plants, the C4 pathway. Present in a subset of plants, the C4 pathway supplemented the earlier C3 photosynthetic pathway, meaning those species now reaped energy from the sun using two different strategies.

Dry conditions may have helped a new type of plant gain a foothold on Earth
Biochemical and paleoclimate modeling revealed that plants with a new photosynthetic pathway known as C4, present
 in several important crop species today, emerged when atmospheric carbon dioxide was still quite high, roughly
30 million years ago. Water limitations, rather than Co2, drove its initial spread, a Penn-led team found
[Credit: Penn State University]

Researchers have long believed that falling carbon dioxide levels drove the origin of plants with this innovation, but a new study in the Proceedings of the National Academy of Sciences, based on biochemical modeling by a group led by University of Pennsylvania biologists and paleoclimate modeling by a group at Purdue University, indicates that water availability may have been the critical factor behind the emergence of C4 plants.

“The initial origin of C4, which happened when atmospheric carbon dioxide was still very high, seems driven by water limitation,” says Haoran Zhou, a graduate student in the School of Arts and Sciences’ Biology Department and first author on the paper. “Then later, about 5 to 8 million years ago, there’s a large expansion of C4 grasslands. That’s because carbon dioxide was getting lower and lower. Carbon dioxide and light intensity were actually the limiting factors favoring C4 at that time.”

“What we show,” says Erol Akçay, an assistant professor of biology at Penn, “is that the increased water efficiency of the C4 pathway is enough to give it an initial ecological advantage in relatively arid environments. That’s the benefit of doing this type of physiological modeling. If you were only looking at temperature and carbon dioxide, you might miss this role of water and light.”

The researchers’ work also suggest that C4 plants may have had a competitive advantage over C3 plants even when carbon dioxide levels in the atmosphere were still relatively high, in the late Oligocene.

“The inference is that C4 could have evolved quite a bit earlier than we previously thought,” says Penn’s Brent Helliker, an associate professor of biology who, along with Akçay, serves as Zhou’s advisor. “This supports some molecular clock estimates for when C4 evolved as well.”

In plants with a C3 photosynthesis pathway, the first stable compound produced in photosynthesis contains three carbon atoms; in C4 plants, the first compound has four carbon atoms. The C3 pathway evolved first, functioning efficiently when the atmosphere was rich with carbon dioxide. However, C4 plants evolved independently from C3 plants dozens of times, able to photosynthesize efficiently in spite of lower carbon levels thanks to an extra step in the process that serves to pump carbon from the air into an internal layer of cells where the rest of the cycle runs. By running this “closed” system, where the photosynthetic machinery doesn’t interact directly with the outside air, C4 photosynthesis enables plants to make more food with less water loss than the C3 pathway.

Today, roughly a quarter of the planet’s vegetative cover is composed of C4 plants. Several important crop species, including maize and sugar cane, possess the C4 pathway. Findings from the fossil record and isotope studies have helped scientists estimate when this pathway evolved, though these estimates have been later than those suggested by molecular clock data from phylogenetic analyses of various plant species, leading to some confusion about when the pathway emerged and when it came to dominate in certain ecosystems.

To look closer at the factors that may have favored the spread of the C4 photosynthetic pathway, Zhou, Akçay, and Helliker created a multi-layered model. They considered variables that affect photosynthesis along with those that influence the hydraulic system, in which plants “decide” to either devote more energy into growing roots to take up water, or into building more leaf matter that can help take in light and carbon dioxide but also exposes them to greater water loss. In addition, plants can determine the optimal balance of carbon gain and water loss. Coupling these two systems, the scientists’ model included four factors that could either favor the C3 or the C4 lineages: carbon dioxide concentration, light, temperature, and water availability.

According to their model, C4 evolution appeared to play out in two phases. When carbon dioxide was still high, C4 emerged in areas of the globe that had become warmer and drier. But it didn’t reap its competitive advantage over C3 plants until several million years later, when carbon dioxide was very low and the expansion of grasslands provided open habitats with ample light. In these regions, C4 grasslands expanded and replaced C3 grasslands.

To see how this model interacted with paleoclimate in the early days of C4 plants, the Penn team collaborated with Purdue University’s Matthew Huber, a paleoclimate modeler funded by the National Science Foundation to model Miocene climate, and graduate student Ashley Dicks. Using climate model output and paleoclimate data including carbon dioxide levels, temperature, and rainfall, the researchers predicted the likely geographic distributions for C3 versus C4 plants through the period from the late Oligocene to the early Miocene, roughly 30 to 5 million years ago. They found two regions that had not previously been identified where C4 plants would have been likely to dominate after first evolving, thanks to their water efficiency: northwestern Africa and Australia.

“These are two previously unrecognized pockets of the world where C4 plants could have had an ecological advantage and really taken over,” Akçay says.

“It was a really exciting opportunity,” says Huber, “when the Penn group reached out to us because this is a really novel application of paleoclimate model output. It helps make the connection between what climate models tells us about past and future climates and verifiable patterns from the geological record.”

Though the study did not investigate what might happen in the future as atmospheric carbon levels rise once again, it can help boost an understanding of why plants are distributed the way they are today and how they might respond to future conditions.

“The climate conditions that were present when C4 evolved are possibly still important today,” says Helliker. “If a lineage of C4 plants evolved primarily because of water limitations when carbon dioxide was high, then those plants may be found in dry environments today, whereas if it was more carbon dioxide that led to their evolution and dominance then those plants might be found in wetter spots today.”

In addition, some scientists believe engineering other agriculturally significant species, such as rice, to have C4 photosynthesis, may help boost food production, so the model could help forecast where such plants could optimally grow.

Source: University of Pennsylvania [November 07, 2018]

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