The Great Acceleration.

 

Iron and Coal, 1855–60, by William Bell Scott illustrates the central place of coal and iron working in the industrial revolution (From Wikimedia Commons)

Iron and Coal, 1855–60, by William Bell Scott illustrates the central place of coal and iron working in the industrial revolution (From Wikimedia Commons)

During a meeting of the International Geosphere-Biosphere Programme (IGBP) celebrated in Mexico, in 2000, the Vice-Chair of IGBP, Paul Crutzen, proposed the use of the term Anthropocene to designate the last three centuries of human domination of earth’s ecosystems, and to mark the end of the current Holocene geological epoch. He suggested that the start date of the Anthropocene must be placed near the end of the 18th century, about the time that the industrial revolution began, and noted that such a start date would coincide with the invention of the steam engine by James Watt in 1784.

Although there is no agreement on when the Anthropocene started, researchers accept that the Anthropocene is a time span marked by human interaction with Earth’s biophysical system. It has been defined, primarily, by significant and measurable increases in anthropogenic greenhouse gas emissions from ice cores, and other geologic features including synthetic organic compounds and radionuclides. Eugene Stoermer, in an interview in 2012, proposed that the geological mark for the Anthropocene was the isotopic signature of the first atomic bomb tests. Hence,  Anthropocene deposits would be those that may include the globally distributed primary artificial radionuclide signal (Zalasiewicz et al, 2015).

 

anthropocene

Alternative temporal boundaries for the Holocene–Anthropocene boundary (calibrated in thousand of years before present) From Smith 2013

 

Human activity is a major driver of the dynamics of Earth system. After the World War II, the impact of human activity on the global environment dramatically increased. This period associated with very rapid growth in human population, resource consumption, energy use and pollution, has been called the Great Acceleration.

During the Great Acceleration, the atmospheric CO2 concentration grew, from 311 ppm in 1950 to 369 ppm in 2000 (W. Steffen et al., 2011). About one third of the carbon dioxide released by anthropogenic activity is absorbed by the oceans. When CO2 dissolves in seawater, it produce carbonic acid. The carbonic acid dissociates in the water releasing hydrogen ions and bicarbonate. Then, the formation of bicarbonate removes carbonate ions from the water, making them less available for use by organisms. Ocean acidification affects the biogeochemical dynamics of calcium carbonate, organic carbon, nitrogen, and phosphorus in the ocean, and will directly impact in a wide range of marine organisms that build shells from calcium carbonate, like planktonic coccolithophores, molluscs,  echinoderms, corals, and coralline algae.

Clastic plastiglomerate containing molten plastic and basalt and coral fragments (Image adapted from P. Corcoran et al., 2014)

Clastic plastiglomerate containing molten plastic and basalt and coral fragments (Image adapted from P. Corcoran et al., 2013)

One important marker for the future geological record is a new type of rock formed by anthropogenically derived materials. This type of rock has been named plastiglomerate, and has been originally described on Kamilo Beach, Hawaii. This anthropogenically influenced material has great potential to form a marker horizon of human pollution, signaling the occurrence of the Anthropocene epoch (Corcoran et al., 2013).

Climate change, shifts in oceanic pH, loss of biodiversity and widespread pollution have all been identified as potential planetary tipping point. Since the industrial revolution, the wave of animal and plant extinctions that began with the late Quaternary has accelerated. Calculations suggest that the current rates of extinction are 100–1000 times above normal, or background levels. We are in the midst of  the so called “Sixth Mass Extinction”.

Dealing with the transition into the Anthropocene requires careful consideration of its social, economic and biotic effects. In his master book L’Evolution Créatrice (1907), French philosopher Henri Bergson, wrote:  “A century has elapsed since the invention of the steam engine, and we are only just beginning to feel the depths of the shock it gave us.”

 

References:

Will Steffen, Wendy Broadgate, Lisa Deutsch, Owen Gaffney, and Cornelia Ludwig. The trajectory of the Anthropocene: The Great Acceleration. The Anthropocene Review, January 16, 2015 DOI: 10.1177/2053019614564785

Jan Zalasiewicz et al. When did the Anthropocene begin? A mid-twentieth century boundary level is stratigraphically optimal. Quaternary International, published online January 12, 2015; doi: 10.1016/j.quaint.2014.11.045

Smith, B.D., Zeder, M.A., The onset of the Anthropocene. Anthropocene (2013),http://dx.doi.org/10.1016/j.ancene.2013.05.001

Ellis, E.C., 2011. Anthropogenic transformation of the terrestrial biosphere. Philosophical Transactions of the Royal Society A 369, 1010–1035.

 

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The Rise of Oxygen and the early animals.

image_1413_1e-palaeosol

Iron formation from the Pongola Supergroup, South Africa. Credit: Nic Beukes/Univ. of Johannesburg.

Earth is the only planet in our Solar System with high concentrations of gaseous diatomic oxygen. Simultaneously, this unique feature of Earth’s atmosphere has allowed the presence of an ozone layer that absorbed UV radiations. But the oxygen content of Earth’s atmosphere has varied greatly through time. For about the first 2 billion years of Earth’s history, the atmospheric oxygen concentration was exceptionally low.

It’s widely assumed that about 2.3 billion years ago, the level of oxygen increased dramatically in a process called the Great Oxidation Event (GOE). This rise in oxygen level occurred during an episode of major glaciation known as the Huronian glaciation. The progressive oxygenation of the atmosphere and oceans was sustained by an event of high organic carbon burial, called the Lomagundi Event, which lasted well over 100 million years, and represents the largest positive carbon-isotope excursion in Earth history (Canfield, 2013). This early oxygen primary production  was exclusively conducted by prokaryotes, specifically by cyanobacteria.

Precambrian stromatolites in the Siyeh Formation, Glacier National Park. From Wikimedia Commons.

Precambrian stromatolites in the Siyeh Formation, Glacier National Park. From Wikimedia Commons.

However, new geochemical  evidence suggested that there were appreciable levels of atmospheric oxygen about 3 billion years ago, more than 600 million years before the Great Oxidation Event, indicating a greater antiquity for oxygen producing photosynthesis and aerobic life.

After the GOE, oxygen levels rose again and then fell in the atmosphere and remained at extremely low levels for more than a billion years. This was probably due to a particular combination of  biogeochemical feedbacks that spawned an oxygen-lean deep ocean (Lyons, 2014). The general oxygenation of the oceans began around 750-550 million years ago. This recovery  of oxygen levels led to a significant increase in trace metals in the ocean and possibly triggered the ‘Cambrian explosion of life’ (Large, 2014).

Halichondria panicea, a temperate marine demosponge (Photo: Daniel Mills)

Halichondria panicea, a temperate marine demosponge (Photo: Daniel Mills)

But early animals, in general, may have had relatively low oxygen requirements. According to new findings, a sea sponge – the living animal that most resembles the earliest animals on Earth – can live and grow even at atmospheric oxygen levels that are 0.5 percent of today’s levels, which challenges the notion that low oxygen levels were the limiting factor for animal evolution. The study also suggest that the evolution of sophisticated gene regulatory networks, may have controlled the timing of animal origins more so than environmental parameters  (Mills, 2014)

References:

Donald E. Canfield, Lauriss Ngombi-Pemba, Emma U. Hammarlund, Stefan Bengtson, Marc Chaussidon, François Gauthier-Lafaye, Alain Meunier, Armelle Riboulleau, Claire Rollion-Bard, Olivier Rouxel, Dan Asael, Anne-Catherine Pierson-Wickmann, and Abderrazak El Albani,  Oxygen dynamics in the aftermath of the Great Oxidation of Earth’s atmosphere PNAS 2013 110 (42) 16736-16741; published ahead of print September 30, 2013, doi:10.1073/pnas.1315570110.

Daniel B. Mills, Lewis M. Ward, CarriAyne Jones, Brittany Sweeten, Michael Forth, Alexander H. Treusch, and Donald E. Canfield, Oxygen requirements of the earliest animals, PNAS 2014 ; published ahead of print February 18, 2014, doi:10.1073/pnas.1400547111

Timothy W. Lyons, Christopher T. Reinhard, Noah J. Planavsky. The rise of oxygen in Earth’s early ocean and atmosphere. Nature, 2014; 506 (7488): 307 DOI: 10.1038/nature13068

Ocean acidification: Anthropocene versus Eocene.

Ammonia beccarii, Benthonic foraminifera. From Wikimedia Commons

Ammonia beccarii, Benthic foraminifera. From Wikimedia Commons

Last week a report from the International Programme on the State of the Ocean (IPSO) declared that ocean acidification has reached an unprecedented level in Earth’s history. Since the Industrial Revolution, the anthropogenic release of CO2 into the Earth’s atmosphere has increased a 40%.
Over the period from 1750 to 2000, the oceans have absorbed approximately one-third of the CO2 emitted by humans. The cost of this is the decrease in surface ocean pH, that cause dramatic effects on marine life.

When CO2 dissolves in seawater, it produce carbonic acid. The carbonic acid dissociates in the water releasing hydrogen ions and bicarbonate. The formation of bicarbonate then removes carbonate ions from the water, making them less available for use by organisms.

Other consequences of an increasingly acidic ocean include effects on metal speciation, reduced NH3/NH4+ ratios and alteration of underwater sound absorption.

Geological context for ocean acidification. (A) Candidate ocean acidification events. (B) Ocean surface pH calculated at 20 million year intervals. (C) Major changes in plankton assemblages. From Kump, 2009.

The geological record of ocean acidification may provide valuable insights for the future of Earth’s climate and how marine organisms could adapt to severe conditions.

The closest analog for today conditions is the Palaeocene–Eocene Thermal Maximum (PETM, approx. 56Ma), meaning greater similarities in continental configuration, ecosystem structure and function, and global carbon cycling.

The PETM was a short-lived (~ 200,000 years) global warming event when temperatures increased by 5-9°C. It was marked by the largest deep-sea mass extinction among calcareous benthic foraminifera in the last 93 million years. Similarly, planktonic foraminifer communities at low and high latitudes show reductions in diversity.

Nannofossil abundance changes during the PETM. From Kump, 2009.

The PETM is also associated with dramatic changes among the calcareous plankton,characterized by the appearance of transient nanoplankton taxa of heavily calcified forms of Rhomboaster spp., Discoaster araneus, and D. anartios as well as Coccolithus bownii, a more delicate form.

Because the PETM is considered the best analog to modern global warming, the changes in the assemblage of calcareous nanoplankton during this event could provide vital clues to the potential response of modern nanoplankton to ocean acidification.

Not only the magnitude but also the time scale of the carbon input is critical for its effect on ocean carbonate chemistry. The time scale of the anthropogenic carbon input is so short that the natural capacity of the surface reservoirs to absorb carbon is overwhelmed.

Comparison of the effects of anthropogenic emissions (total of 5000 Pg C over 500 years) and PETM carbon release (3000 Pg C over 6 kyr) on the surface ocean saturation state of calcite. From Zeebe, 2013

So, the anthropogenic carbon input rate is probably greater than during the PETM, causing a more severe decline in ocean pH and saturation state. Also the biotic consequences of the PETM were fairly minor, while the current rate of species extinction is already 100–1000 times higher than would be considered natural. This underlines the urgency for immediate action on global carbon emission reductions.

Trevor Manuel, a South African government minister and co-chair of the Global Ocean Commission stated that “Governments must respond as urgently as they do to national security threats – in the long run, the impacts are just as important”.

References:

Zeebe RE and Zachos JC. 2013 Long-term legacy ofmassive carbon input to the Earth system: Anthropocene versus Eocene. Phil Trans R Soc A 371: 20120006. http://dx.doi.org/10.1098/rsta.2012.0006.

Kump, L.R., T.J. Bralower, and A. Ridgwell. 2009. Ocean acidification in deep time. Oceanography 22(4):94–107, http://dx.doi.org/10.5670/oceanog.2009.100