Onset of the Anthropocene

For at least 50 years we have been living in the Anthropocene Epoch, and until recently all of us Anthropos (Greek for human beings) were completely unaware of it. Of course, most people are generally unaware of our place in geologic time and the Anthropocene Epoch technically does not exist yet, but the scientific endeavor to define the beginning of the Anthropocene Epoch represents our effort to recognize a time after which human activity irreversibly changed the climate ensuring a planetary global warming event that has already changed the course of planetary evolution. Humans are a powerful climate forcing variable, but we have wielded our power in a way that is detrimental. Yet, we still have the chance to change the course of planetary evolution and choose to use our knowledge and power to create a future that supports climate equilibrium and ecosystem stability. Our choice will be recorded in the rocks that form upon the surface of the planet, and our decisions will be forever evident in Earth's planetary record.

The story of Earth is recorded in rocks, the materials that form as the outer layer of the planet changes over thousands and millions of years. I taught a 6-week OLLI course entitled "The Story of Earth Conveyed by Rocks" in spring 2022, and over the course of 12 hours I shared evidence of the four and a half billion year evolution of the planet. We looked at rocks and fossils that represent key changes to Earth systems, such as the formation of the moon, the oxygenation of the atmosphere and oceans, the evolution of macroscopic life, the formation and destruction of supercontinents, and the role that large igneous provinces (truly massive volcanic eruptions) have played in mass extinctions that have changed the course of life on Earth. Twelve hours was not enough to cover 4,540 million years of time, and I could easily spend dozens of hours focusing on just a few hundred million years of earth history. Much of the knowledge Geologists have gained from observing the material and chemical changes Earth has experienced is now informing us that the current human-caused climate predicament is comparable only to destructive geologic events that occurred millions of years ago. We hope that we can use the knowledge of the past to prevent a cataclysmic event of our own making, because the rock record shows that rapid climate change events (RCCEs) and associated mass extinctions are not rare throughout geologic time. In fact, the geologic time scale is largely organized around mass extinction events.

The geologic time scale is a human construct, we created it to bring order to the immensity of Earth time, aka deep time (Ma = millions of years ago). This construct is constantly evolving, because our knowledge of Earth history is constantly increasing. The divisions of the geologic time scale are marked by GSSPs (Global Boundary Stratotype Section and Point) or more excitingly referred to as "Golden Spikes". The International Commission on Stratigraphy uses physical and chemical features of rocks to determine where geologic time scale divisions are best represented on Earth. We literally place a bronze disk (not gold) into a rock face marking the point in the stratigraphy (layers of rock) where the division of the geologic time changes. The image below is the GSSP for the start of the Ediacaran Period, located in the Ediacara Hills of Australia where famous fossils exist of soft bodied organisms that lived before the Phanerozoic Eon, Paleozoic Era, and Cambrian Period began. Each GSSP marks a pronounced change on Earth, a biological innovation, a mass extinction and/or a significant climatic shift.

About 10 GSSPs are on North America, including the following famous 'golden spikes':

• Fortune Head, Newfoundland in Canada = the end of the Precambrian Super-Eon that includes ~8/9ths of Earth history, and the beginning of the Phanerozoic Eon/Paleozoic Era/Cambrian Period 538.8 million years ago when the ancestors of the major lineages of animals with skeletons begin to appear in the fossil record

• Green Point, Newfoundland in Canada = the end of the Cambrian Period and the beginning of the Ordovician Period 485.4 million years ago, when an important conodont (weird, creepy, and now extinct vertebrate) evolved in the oceans

• Arrow Canyon, Nevada = the end of the Mississippian Period and the beginning of the Pennsylvanian Period 323.2 million years, when the oldest land dwelling 4 limbed creatures started to lay their eggs on land

In addition to GSSPs representing divisions of the geologic time scale, they also literally mark the geographic locations where we obtain scientific evidence of changes in biological evolution and planetary climate. Earth history is a catalog of the evolution of the surface of the planet, the life on the surface of the planet, and the ever fluctuating climate that determines where life can thrive and when it is doomed to extinction. Our knowledge of climate change over 4.54 billions years of Earth time is obtained from the rocks, the record of changing surface conditions. The geologic time scale is just the way we organize that information, and since we gain new information every day the geologic time scale will continue to evolve.

Until the Anthropocene Epoch is realized, we are living in the Holocene Epoch, the last division of the Cenozoic Era. The Cenozoic (means 'recent life') Era is divided into epochs that break-up the last 66 million years. The term 'cene" comes from the latin word 'recens', meaning recent or new. 'Holos' is greek for whole or well-kept or entirely, so Holocene means 'entirely new'. The Holocene Epoch started 11,700 years ago when the last glacial stage ended and natural warming processes initiated the interglacial stage of the current ice age that we live within today. In this interglacial stage that we call the Holocene Epoch humans have changed the surface of the Earth through agriculture, civilization, pollution, hunting, fishing, transporting invasive species, genetic modification of plants and animals, and exponential human population growth. In the last century this mark upon the Earth has yielded consequences that are comparable only to destructive geologic events that occurred millions of years ago that we have learned of through our observations of the rock record.

It was decided in the early 2000s that the Holocene Epoch would need to come to a conclusion to mark the onset of the Anthropocene Epoch during the mid-20th century, the epoch during which the mark of human activity is so profound that it is recorded in the rocks and will be evidence of our impact on the planet for all time. This golden spike has not yet been officially chosen, but there are 12 contenders and 4 are in North America...including 2 in California, and one of which is the San Francisco Estuary. This distinction is now part of the geologic history of California, because the ecosystem of the San Francisco Bay has been "wholly changed by organisms introduced" by human activities. When geologists named the Holocene Epoch they had no idea that the name 'entirely new' would represent such massive change to the surface of the planet, wrought by a single species named homo sapiens, aka 'wise human'. The Anthropocene Epoch division will serve to remind us that we have left our mark on the planet, and at this point that mark is not something we can be proud of since it is the pollution and destruction of the ecosystem that marks the beginning of the 'epoch entirely of humans', but we can still change the way we use the resources of the planet. That mark can evolve from destructive to supportive...if we choose to support the ecosystem we rely on rather than taking that which we want with no regard for the consequences to the inhabitants of planet Earth. Individually we can be more mindful of what we buy, how we dispose of our waste, and by supporting economic and political changes towards a more sustainable future, but the choice is ultimately one the entirety of the homo sapiens species must make...I wonder how wise our choice will be during the remainder of the Anthropocene Epoch.