* Astronomy

An ancient 'Great Leap Forward' for life in the open ocean

Plankton in the Earth's oceans received a huge boost when microorganisms capable of creating soluble nitrogen 'fertilizer' directly from the atmosphere diversified and spread throughout the open ocean. This event occurred at around 800 million years ago and it changed forever how carbon was cycled in the ocean.
It has long been believed that the appearance of complex multicellular life towards the end of the Precambrian (the geologic interval lasting up until 541 million years ago) was facilitated by an increase in oxygen, as revealed in the geological record. However, it has remained a mystery as to why oxygen increased at this particular time and what its relationship was to 'Snowball Earth' - the most extreme climatic changes the Earth has ever experienced - which were also taking place around then.
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Ancient soils provide early whiff of oxygen

Oxygen may have been accumulating in Earth's atmosphere hundreds of millions of years earlier than we thought.
An international team has made the claim in Nature magazine after studying the oldest soils on Earth.
The researchers say elements in the three-billion-year-old material show evidence for oxidative weathering.
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Great Oxidation Event: More oxygen through multicellularity

The appearance of free oxygen in the Earth's atmosphere led to the Great Oxidation Event. This was triggered by cyanobacteria producing the oxygen which developed into multicellular forms as early as 2.3 billion years ago. As evolutionary biologists from the Universities of Zurich and Gothenburg have shown, this multicellularity was linked to the rise in oxygen and thus played a significant role for life on Earth as it is today.
Cyanobacteria belong to the Earth's oldest organisms. They are still present today in oceans and waters and even in hot springs. By producing oxygen and evolving into multicellular forms, they played a key role in the emergence of organisms that breathe oxygen. This has, now, been demonstrated by a team of scientists under the supervision and instruction of evolutionary biologists from the University of Zurich. According to their studies, cyanobacteria developed multicellularity around one billion years earlier than eukaryotes - cells with one true nucleus. At almost the same time as multicellular cyanobacteria appeared, a process of oxygenation began in the oceans and in the Earth's atmosphere.
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Title: Rethinking the Paleoproterozoic Great Oxidation Event: A Biological Perspective
Authors: John W. Grula (Observatories of the Carnegie Institution for Science, Pasadena, CA, USA)

Competing geophysical/geochemical hypotheses for how Earth's surface became oxygenated - organic carbon burial, hydrogen escape to space, and changes in the redox state of volcanic gases - are examined and a more biologically-based hypothesis is offered in response. It is argued that organic carbon burial is of minor importance to the accumulation of oxygen in a mainly anoxic world where aerobic respiration is not globally significant. Thus, for the Great Oxidation Event (GOE) ~ 2.4 Gyr ago, an increasing flux of O2 due to its production by an expanding population of cyanobacteria is parameterised as the primary source of O2. Various factors would have constrained cyanobacterial proliferation and O2 production during most of the Archean and therefore a long delay between the appearance of cyanobacteria and oxygenation of the atmosphere is to be expected. Destruction of O2 via CH4 oxidation in the atmosphere was a major O2 sink during the Archean, and the GOE is explained to a significant extent by a large decline in the methanogen population and corresponding CH4 flux which, in turn, was caused primarily by partial oxygenation of the surface ocean. The partially oxygenated state of these waters also made it possible for an aerobic methanotroph population to become established. This further contributed to the large reduction in the CH4 flux to the atmosphere by increasing the consumption of CH4 diffusing upwards from the deeper anoxic depths of the water column as well as any CH4 still being produced in the upper layer. The reduction in the CH4 flux lowered the CH4 oxidation sink for O2 at about the same time the metamorphic and volcanic gas sinks for O2 also declined. As the O2 source increased from an expanding population of cyanobacteria - triggered by a burst of continent formation ~ 2.7-2.4 Gyr ago - the atmosphere flipped and became permanently oxygenated.

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