THE ANTHROPOCENE: HAVE WE CREATED A NEW GEOLOGICAL TIME INTERVAL?

The term “Anthropocene” was coined by Paul Crutzen 16 years ago to mark the present as distinct from previous geological time. The term has since flourished in both scientific and popular publications, but without definition it has developed many meanings. In 2009 the Anthropocene Working Group (AWG) was established to advise the Subcommission on Quaternary Stratigraphy (SQS), the body responsible for classification of the past 2.6 million years of Earth history, on the term’s merit and potentially to propose a definition based upon the geological evidence. The quest to subdivide geological time into sensible and strictly defined units, of the Geological Time Scale http://www.stratigraphy.org/index.php/ics ‐ chart ‐ timescale , is one of the cornerstones of the geological sciences and decisions to incorporate new units are not taken lightl

Control of solar sail periodic orbits in the elliptic three-body problem

A solar sail essentially consists of a large mirror that uses the momentum change due to photons reflecting off the sail for its impulse. Solar sails are therefore unique spacecraft, as they do not require fuel for propulsion [1]. In this Note we consider using the solar sail to continuously maintain a periodic orbit above the ecliptic plane using variations in the sail's orientation. Positioning a spacecraft continuously above the ecliptic would allow continuous observation and communication with the poles

Carboniferous geology of Northern England

The British Geological Survey (BGS) has produced a wholesale rationalisation of Carboniferous lithostratigraphical nomenclature. This presentation describes the Carboniferous stratigraphy of northern England, illustrated with research carried out as part of recent BGS mapping projects. During the Tournaisian and Visean a phase of north–south rifting resulted in the development of grabens and half-grabens, separated by platforms and tilt-block highs. Visean marine transgressions resulted in the establishment of platform carbonates, which gradually onlapped raised horst and tilt-block highs. The evolution of one such tilt-block high, the Askrigg block, and associated Great Scar Limestone Group, is described in detail. During late Visean times a cyclic succession of fluvio-deltaic clastics, marine reworked sandstones and shallow-shelf marine carbonates (Yoredale Group) dominated across northern England, terminating deposition of the platform carbonates. To the south of the Craven fault system, which defines the southern margin of the Askrigg Block, the block and basin structures persisted, though generally the high subsidence rates created a province dominated by hemipelagic mudstones and carbonate/siliciclastic turbidites (Craven Group). Cessation of rifting during the late Visean in the area between the Southern Uplands and the Wales–Brabant High resulted in a period dominated by thermally induced regional subsidence during Namurian and Westphalian times, with formation of the Pennine Basin. During early Namurian times fluvio-deltaic systems started to feed siliciclastic sediment into the northern margin of the basin (Millstone Grit Group). Initial deposition in the basinal areas is marked by the formation of thick turbidity-fronted delta successions. By late Namurian times, the southern part of the basin began to be infilled by fluvio-deltaic systems entering the basin from the east and south-east, but ultimately still sourced from the north. Three case studies are described in detail: the Kinderscout Grit, Ashover Grit and Chatsworth Grit. The development of these sand bodies occurred within a regime of regular and marked sea level changes. Evidence will be provided for the duration of this cyclicity. From early in the Westphalian, a coal-forming delta-top environment, associated with formation of the Pennine Coal Measures Group became established across the Pennine Basin. There was gradual waning of the influence of marine flooding events in the basin. The sediment influx into the Pennine Basin progressively changed from a dominantly northern provenance, comparable to the Millstone Grit Group, to initially a western source and subsequently to a southern one, later in the Westphalian

Invariant manifolds and orbit control in the solar sail three-body problem

In this paper we consider issues regarding the control and orbit transfer of solar sails in the circular restricted Earth-Sun system. Fixed points for solar sails in this system have the linear dynamical properties of saddles crossed with centers; thus the fixed points are dynamically unstable and control is required. A natural mechanism of control presents itself: variations in the sail's orientation. We describe an optimal controller to control the sail onto fixed points and periodic orbits about fixed points. We find this controller to be very robust, and define sets of initial data using spherical coordinates to get a sense of the domain of controllability; we also perform a series of tests for control onto periodic orbits. We then present some mission strategies involving transfer form the Earth to fixed points and onto periodic orbits, and controlled heteroclinic transfers between fixed points on opposite sides of the Earth. Finally we present some novel methods to finding periodic orbits in circumstances where traditional methods break down, based on considerations of the Center Manifold theorem

The Anthropocene

The Anthropocene hypothesis—that humans have impacted “the environment” but also changed the Earth’s geology—has spread widely through the sciences and humanities. This hypothesis is being currently tested to see whether the Anthropocene may become part of the Geological Time Scale. An Anthropocene Working Group has been established to assemble the evidence. The decision regarding formalization is likely to be taken in the next few years, by the International Commission on Stratigraphy, the body that oversees the Geological Time Scale. Whichever way the decision goes, there will remain the reality of the phenomenon and the utility of the concept. The evidence, as outlined here, rests upon a broad range of signatures reflecting humanity’s significant and increasing modification of Earth systems. These may be visible as markers in physical deposits in the form of the greatest expansion of novel minerals in the last 2.4 billion years of Earth history and development of ubiquitous materials, such as plastics, unique to the Anthropocene. The artefacts we produce to live as modern humans will form the technofossils of the future. Human-generated deposits now extend from our natural habitat on land into our oceans, transported at rates exceeding the sediment carried by rivers by an order of magnitude. That influence now extends increasingly underground in our quest for minerals, fuel, living space, and to develop transport and communication networks. These human trace fossils may be preserved over geological durations and the evolution of technology has created a new technosphere, yet to evolve into balance with other Earth systems. The expression of the Anthropocene can be seen in sediments and glaciers in chemical markers. Carbon dioxide in the atmosphere has risen by ~45 percent above pre–-Industrial Revolution levels, mainly through combustion, over a few decades, of a geological carbon-store that took many millions of years to accumulate. Although this may ultimately drive climate change, average global temperature increases and resultant sea-level rises remain comparatively small, as yet. But the shift to isotopically lighter carbon locked into limestones and calcareous fossils will form a permanent record. Nitrogen and phosphorus contents in surface soils haves approximately doubled through increased use of fertilizers to increase agricultural yields as the human population has also doubled in the last 50 years. Industrial metals, radioactive fallout from atomic weapons testing, and complex organic compounds have been widely dispersed through the environment and become preserved in sediment and ice layers. Despite radical changes to flora and fauna across the planet, the Earth still has most of its complement of biological species. However, current trends of habitat loss and predation may push the Earth into the sixth mass extinction event in the next few centuries. At present the dramatic changes relate to trans-global species invasions and population modification through agricultural development on land and contamination of coastal zones. Considering the entire range of environmental signatures, it is clear that the global, large and rapid scale of change related to the mid-20th century is the most obvious level to consider as the start of the Anthropocene Epoch

Tales from a Geological Adventurer

Dr Colin Waters joined BGS in 1988 straight after completing his PhD from Cardiff University and is currently Acting Chief Geologist for Geology and Landscapes England. He has worked on a wide range of projects over the years, several of which have included adventures in the vast remote corners of the world

Anthropocene

The world today is undergoing rapid environmental change, driven by human population growth and economic development. This change encompasses such diverse phenomena as the clearing of rainforests for agriculture, the eutrophication of lakes and shallow seas by fertilizer run-off, depletion of fish stocks, acid rain, and global warming. These changes are cause for concern—or alarm—among some, and are regrettable if unavoidable side effects of economic growth for others

Human bioturbation, and the subterranean landscape of the Anthropocene

Bioturbation by humans (‘anthroturbation’), comprising phenomena ranging from surface landscaping to boreholes that penetrate deep into the crust, is a phenomenon without precedent in Earth history, being orders of magnitude greater in scale than any preceding non-human type of bioturbation. These human phenomena range from simple individual structures to complex networks that range to several kilometres depth (compared with animal burrows that range from centimetres to a few metres in depth), while the extraction of material from underground can lead to topographic subsidence or collapse, with concomitant modification of the landscape. Geological transformations include selective removal of solid matter (e.g. solid hydrocarbons, metal ores), fluids (natural gas, liquid hydrocarbons, water), local replacement by other substances (solid waste, drilling mud), associated geochemical and mineralogical changes to redox conditions with perturbation of the water table and pH conditions and local shock-metamorphic envelopes with melt cores (in the case of underground nuclear tests). These transformations started in early/mid Holocene times, with the beginning of mining for flint and metals, but show notable inflections associated with the Industrial Revolution (ca 1800 CE) and with the ‘Great Acceleration’ at ∼1950 CE, the latter date being associated with the large-scale extension of this phenomenon from sub-land surface to sub-sea floor settings. Geometrically, these phenomena cross-cut earlier stratigraphy. Geologically, they can be regarded as a subsurface expression of the surface chronostratigraphic record of the Anthropocene. These subsurface phenomena have very considerable potential for long-term preservation

Anthropocene: its stratigraphic basis

As officers of the Anthropocene Working Group (AWG; J.Z. and C.W.) and chair of the Subcommission on Quaternary Stratigraphy (SQS; M.J.H.) of the International Commission on Stratigraphy (ICS), we note that the AWG has less power than Erle Ellis and colleagues imply (Nature 540, 192–193; 2016). Its role is merely advisory — to evaluate the Anthropocene as a formal unit in the geological timescale. Proposals must pass scrutiny by the AWG, the SQS and the ICS before being ratified by the Executive Committee of the International Union of Geological Sciences

Second Anthropocene Working Group meeting

The second meeting of the Anthropocene Working Group (AWG) was held at the McDonald Institute for Archaeological Research, University of Cambridge, on 24th and 25th November 2015. It took the form of a workshop with 12 members of the working group and numerous archaeologists from the Institute in lively conversation with each other. Discussion was focused on anthropogenic strata and matters of chronostratigraphy. The AWG was set up in 2009 to consider the case for formalizing the term ‘Anthropocene’ in the Geological Time Scale. The working group reports to the Subcommission on Quaternary Stratigraphy, which sits within the broader framework of the International Commission on Stratigraphy (ICS). Unusually for a working group of the ICS, it consists of researchers from a wide variety of Earth Sciences, including archaeology