Chalk from the Anthropocene: lime mud

A lump of lime mud. A precursor to chalk made by a culture of Coccolithophora and the sedimentation by its dead cells.

A lump of lime mud. A precursor to chalk made by a culture of Coccolithophora and the sedimentation of  its dead cells.

A lump of lime mud. A precursor to chalk made by a culture of Coccolithophora and the sedimentation by its dead cells.

A lump of lime mud. A precursor to chalk made by a culture of Coccolithophora and the sedimentation of its dead cells.

A lump of lime mud. A precursor to chalk made by a culture of Coccolithophora and the sedimentation by its dead cells.

A lump of lime mud. A precursor to chalk made by a culture of Coccolithophora and the sedimentation of  its dead cells.

Here some lumps of the lime mud have been trapped between two microscope slides and mixed with an acid. This treatment liberates the trapped carbon dioxide which can be seen as bubbles.

Here some lumps of the lime mud have been trapped between two microscope slides and mixed with an acid. This treatment liberates the trapped carbon dioxide which can be seen as bubbles.

Chalk is formed when lime mud is transformed into rock by geological processes. Usually, this calcium carbonate rich mud accumulates on the seafloor, more  calcareous sediment builds up on top of it, and as the sea floor subsides, the lime mud is subjected to heat and pressure. These processes remove water and compact the sediment into rock. The lime mud itself is formed from the skeletons of microscopic plankton, which rain down on the sea floor from the sunlit waters above and a group of microbes called the Coccolithophores are considered to be the most important group of chalk forming plankton. Each individual Coccolithophore cell has a spherical skeleton made from a number of calcium carbonate rich discs called coccoliths which after death, fall to the floor of the oceans to generate lime mud. Most of chalk edifices that we are familiar with formed during the Cretaceous period, between 100 and 60 million years ago, and reflect a period when global temperatures, concentrations of greenhouse gases and sea levels were exceptionally high.

We now live in an age when humans and our activities are having a significant global impact on the Earth’s ecosystems and its climate. The Anthropocene is an informal term for the proposed geological epoch that began when human activities began to have such a global impact including increases in global temperatures, concentrations of greenhouse gases and sea levels. This work explores the parallel between the Cretaceous period and the Anthropocene, in that is seeks to make chalk of Anthropocene origin and which also will  include locked in anthropogenic carbon dioxide from the burning of fossil fuels. For a period of six months, air has been bubbled through a culture of mixed Coccolithophora species, and I have been successful in the first steps of chalk production, that is the production of a lime mud, the essential precursor to chalk.

 

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