Saturday, December 17, 2016

So What Is The "Anthropocene" Anyway?

Short answer is that if a proposal by international group of scientists is accepted, the Anthropocene will be the newest member of the geologic time scale.

Before the advent of radiometric dating, which allowed geologists to know with a decent degree of precision how old rocks are, geologists used a relative time scale, based on the types of fossils or major changes in geologic strata. Until the beginning of the 20th century, all a geologist could tell you is that rocks containing the bones of dinosaurs were younger than rocks containing the shells of trilobites, but not how much younger.

So geologists created a time scale which broke down the history of the Earth into ever smaller groupings called Eons, Eras, Periods, and Epochs. Therefore, we live in the Holocene Epoch of the Quaternary Period of the Cenozoic Era of the Phanerozoic Eon. Got it?

The Cenozoic started 65 million years ago, with the extinction of the dinosaurs. The Quaternary started about 2.6 million years ago, when the Earth started into a cycle of periodic worldwide glaciations. The Holocene started about 11,700 years ago, with the end of the last ice age.

The term "Anthropocene" is derived from Greek for human and recent. The idea of the Anthropocene is not new and geologists as far back as the late 1800s looked at humanity's effect on the planet and thought we were entering a new geologic era defined by man's impact on the planet.

The key here is whether human impact on the planet is leaving a definable imprint on the geologic record. The short answer to that question is yes. The decision regarding when the Anthropocene starts will be based on which imprint is chosen because there are several.

Anyone who doubts that humans are changing the planet need only drive down Rte. 9 in Westborough and look at the pile of dirt in front of the Car Max site. A few excavators made that pile in just a few days. It would take nature tens of thousands of years to redistribute that much material in this neck of the woods, short of some catastrophe like a major earthquake or flood event. In fact, humans move more dirt and rock in a given year than all natural erosion processes combined.

Changes in how sediments get to and are deposited in the oceans are being caused by deforestation, damming of rivers, construction of roads and cities, among other human activities. If it weren't for the active intervention of the Corps of Engineers, the Mississippi River would have shifted course to the Atchafalaya River basin in Western Louisiana decades ago, changing how sediments are deposited in the Gulf of Mexico.

Humans are driving changes in the distribution of organisms around the planet and it is a documented fact that humans are driving many forms of life to extinction at a rate many times that which might be expected to occur if we weren't around. I mentioned above that geologists used to define geologic time by changes in the fossil record. Those changes usually coincide with extinction events, like the demise of the dinosaurs.

Mercury from the burning of coal and a radioactive elements derived from nuclear fallout are also detectable in sediments deposited in the oceans and large bodies of freshwater. And of course, humans are changing the atmosphere. Scientists have long been able to make accurate estimates of how the Earth's atmosphere has changed over geologic time. Glaciologists have studied air trapped in glacial ice going back almost 800,000 years. Further back than that, the composition of the atmosphere can be deduced from the distribution of isotopes of carbon, oxygen and other elements bound up in the fossils of microorganisms deposited on the sea floor.

This is how we know what the composition of the atmosphere has been for many millions of years in the past and how we know that atmospheric changes which have occurred over the last century are unprecedented in the geologic record at least since the beginning of the Cenozoic, some 65 million years ago.

A 2014 paper published in the journal "Geology" discussed how the 6 billion tons of plastic produced since 1950 are starting to show up in the geologic record. A new term has been coined for one type of this material: "plastiglomerate". Plastiglomerate forms when plastic is melted into fragments of rock and sand, such as when soda bottles or other refuse are thrown into a bonfire. The stuff is incredibly tough and resistant to breakdown. Scientists expect it will be found in coastal regions throughout the world, wherever humans and plastic and beaches are in the same place at the same time.

The article stated "Our results indicate that this anthropogenically influenced material has great potential to form a marker horizon of human pollution, signaling the occurrence of the informal Anthropocene epoch."

So, in a million years or so, long after our civilization has turned to dust, the most durable marker of human presence on Earth may be random gobs of melted plastic left in sandstone by drunken beach partiers.

Food for thought on a cold winter's day.

Originally published in the Westborough News on 01/22/2016

No comments:

Post a Comment