Tuesday, June 3, 2014


The latest issue of GSA Today (June 2014), a monthly publication of the Geological Society of America, has an interesting paper titled "An anthropogenic marker horizon in the future rock record" by Dr. Patricia Corcoran, et al.

Let me back up a minute first to explain the significance of this.  Geologists divide the four and a half billion years of time since the origin of the Earth into Eons, Eras, Periods, and Epochs of the geologic time scale.  We are currently in the Phanerozoic Eon, Cenozoic Era, Quaternary Period, and Holocene Epoch.

Recently, a number of scientists have proposed the idea that we're in a new Epoch - the Anthropocene (from anthropos which means "man" or "human" in Greek).  While not yet an official part of the geologic time scale, it is getting wide usage with people arguing about how to precisely define the start of such an Epoch.  All rational people, however, agree that humans have made an impact on our global environment that we can directly measure (one that will be preserved in the geologic record for future generations - if they still exist - to measure as well).

There is some disagreement, though, as to where to start the Anthropocene Epoch.  Some suggest measurable changes in soil composition which have occurred over the past few thousand years due to the advent of large-scale agricultural practices by human societies.  Others advocate a more recent date due to measurable changes from the Industrial Revolution (pollutants).  Yet others argue that it should start in the 1950s with the advent of plastics and presence of trace isotopes from atomic bomb testing.

Back to the paper - Corcoran and her colleagues noted the formation of what they called plastiglomerates forming on the Big Island of Hawaii.  While traditional conglomerates are sedimentary rocks formed by pebbles and sand chemically cemented together (lithified), plastiglomerates are described as "... an indurated multi-composite material made hard by agglutination of rock and molten plastic."  The molten plastic was not derived from hot lava flows, as one might suspect from the location, but rather from simple burning of plastic waste in campfires.

Corcoran, et al. 2014 GSA Today

Anthropogenically-derived rocks such as these plastiglomerates will survive in the geologic record recording the Anthropocene Epoch and the unfortunate human habit of shitting in our own nest.

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