Permian Reef – November 11, 2020
Tomorrow we are headed to climb Texas’ high point: Guadalupe Peak at 8,751 feet/2,667 meters, located near the New Mexico border. This is a really unique area, as the top of Texas actually used to be underwater hundreds of millions of years ago! The state highpoint is, in fact, a fossil reef that dates back to the Permian time period (299 – 252 million years ago). It’s hard to imagine what the world looked like hundreds of millions of years ago, particularly in this region as the ancient reef now towers over the dry Chihuahuan desert!
The dinosaurs went extinct a long time ago: 65 million years ago. But when this reef was being built, 265 million years ago, the dinosaurs didn’t even exist yet! Not only that, all the continents were combined into a giant landmass called Pangea and surrounded by a global ocean called Panthalassa. Texas used to be near the equator but the break-up of Pangea and continental drift over millions of years brought it to its current location at 32 degrees North.
The sea that allowed the reef to form was actually an inland sea connected to the Panthalassa Ocean by a narrow channel. Reefs are a fascinating fusion of biology and geology, in that they are made of stone—but built by life. Today, reefs are built mostly by corals. But 265 million years ago, the main builders were other creatures like sponges (Gigantospongia, which had skeletons strengthened by limestone scaffolding and could grow to more than 8 feet across!) as well as billions of foraminifera, or, single-celled lifeforms that live inside shells, measuring from microscopic to 4 inches across.
When the channel to Panthalassa was cut off, this caused the sea to evaporate and for the reef to get covered by sediments. Tectonic forces eventually pushed up the rocks bearing the reef, the softer sediments washed away due to erosion, and this exposed the harder limestone which bore traces of life from a world long ago vanished. The end of the Permian is particularly interesting to scientists in that it ended – geologically speaking – instantaneously (ranging from just a few centuries to thousands of years), leading to 96% extinction of marine species and 70% of land species. What led to this extraordinary wipe-out? The leading hypothesis is massive volcanic eruptions in the Siberian Traps of Russia, which spewed over 4 million cubic kilometers of lava. Immense and sustained eruptions can release huge amounts of sulfur dioxide and carbon dioxide, acidifying the oceans as well as heating the atmosphere. The Permian wipeout is a good analog to our current global changes (though in this case, human-induced) in that it reveals what can happen when an environmental tipping point is passed (very large amounts of greenhouse gases in the atmosphere and ocean), resulting in catastrophic effects to life on the planet.
photo: U. Horodyskyj