Extinction of the mammoth and the Clathrate Gun

Joanne Ballard and André Bijkerk (USA) In this article, we will argue that the extinction of megafauna on the mammoth steppes of the Northern Hemisphere may ultimately have been caused by the release of massive quantities of methane in the North Atlantic Ocean at the Amazon Fan near the Brazilian coast and also from the Ormen Lange gas field off the coast of Norway. We will suggest that these events caused significant changes in the flow of water at the surface of the ocean that, in turn, led to very rapid changes in the levels of rainfall. Scientists have already recognized that increased precipitation gave rise to changes to ecosystems (or, more precisely, to biotopes) that destroyed the mammoth steppe. However, much of the evidence we will use in this article to support our argument has been used to support other sorts of explanation for the extinction. Therefore, this primary evidence now appears to be in need of revision. Introduction About 11,000 years ago, all of the remaining herds of mammoths suddenly disappeared. During the Pleistocene, these mammoths once thrived on a vast, megafauna steppe stretching across the Northern Hemisphere. It may have resembled the African steppes of today with lions, hyenas and several species of large grazers being present. However, the debate about the cause(s) of the extinction continues. In North America, things appear to be simple – the appearance of early humans on that continent seems to coincide with the downfall of the megafauna. However, there are also … Read More

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Giant’s Causeway (Part 1): An introduction

Dr Trevor Watts (UK) This is the first of two articles on the volcanicity of the Giant’s Causeway and the surrounding area. The Causeway itself is an area of basalt columns, about 100m or so across, jutting into the Irish Sea. A remnant of a vast ancient lava flow, it is located in a coastal strip that is lavishly scattered with other superb volcanic features. The whole area is both beautiful and fascinating, and neither spoilt in any way, nor over-crowded out of season. We (my wife Chris and I) went there because I had a few days’ work in Northern Ireland and it seemed like a good idea to combine this with a short break during an October, half-term school holiday. Fig. 1. The Giant’s Causeway, battered by curling waves, becomes a sunlit wonderland in the evening light of autumn. The geology of the Giant’s Causeway The long-held theory that the Causeway was created by an Irish giant called Finn MacCool in Middle Earth times has – sadly – been discredited. Around 60mya (in early Tertiary times), great masses of molten rock were rising from the depth of the earth’s mantle, probably centred beneath present-day Greenland. These nation-sized ‘lava-lamps’ are collectively considered to be a ‘hot spot’, now known as the ‘Iceland Plume’. They split the earth-wide continent of Pangaea apart in great cracks that were aligned roughly northwest to southeast. This was sufficient to split the land apart on a vast scale, beginning the opening of the Atlantic … Read More

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Warming medieval climate supports a revolution in agriculture

Steven Wade Veatch and Cheryl Bibeau (USA) In the light of our current worries about climate change and global warming, this is the first a series of articles for Deposits that covers significant climate changes that have occurred in the geological past and times when the earth’s climate was hugely different from what we know today. However, this first one covers a slightly more recent event – the Medieval Warm period. The twenty-first century has had some of the hottest temperatures on record, but there was another period that was just as warm or warmer. The Medieval Warm Period (approximately 900–1300 AD), refers to the time when temperatures in Europe and nearby regions of the North Atlantic are thought to have been similar to, or in some places exceeded, temperatures of the late twentieth century. Researchers believe changes in the circulation of the Atlantic Ocean brought warmer waters to the North Atlantic and neighbouring regions, causing warming temperatures. The Medieval Warm Period was followed by the Little Ice Age (approximately 1300-1850 AD), a period of cooling that brought colder winters and advancing glaciers to parts of Europe and North America that lasted well into the nineteenth century. Scientists have evidence of this unusual warming period through indirect estimates of temperatures based on climate indicators that include tree rings, Greenland ice cores, ocean sediments and, in certain regions, written evidence of crop yields. There are even recorded dates when leaves come out and when flowers bloom in the spring. Records show … Read More

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Geology of East Greenland

James Cresswell (UK) Eighty percent of Greenland is covered by ice and, in places, this is up to 3.4km thick. So, Greenland might not immediately spring to mind as a place to go to observe rocks. However, it is a huge country and the ice-free area, at 410,000km2, is nearly twice the size of the UK. This is generally sparsely vegetated, leaving the rocks beautifully exposed and the geology incredibly easy to see. The area of East Greenland around Scoresby Sund, Kong Oscar and Kejser Franz Joseph Fjords is the largest ice-free area in Greenland. It also has incredible geodiversity, with basement rocks as old as three billion years, an almost complete sedimentary record of the last 1.6byrs and huge volumes of flood basalts from the splitting of the Atlantic. If you were an alien and wanted to try to piece together the geological story of Planet Earth – but could only visit one area – East Greenland would be the place to go. Fig 1. A simplified geological map of East Greenland. The geological history of Greenland is vastly long and spans 3.8byrs. Its oldest rocks are the 3.8byr-old Isua Complex, situated in West Greenland, near the capital Nuuk. These rocks are the Earth’s oldest, most well-preserved sedimentary and volcanic rocks, and they contain carbon particles that most likely originate from the oldest known life on the planet. To put into perspective just how old these rocks are, try to imagine that the planet is only one year old. … Read More

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