27 November 2017
An hour ago, I asked if anyone recognized this green book, known among geologists as The Green Book.
It’s in a small roadside cafe, the Osteria del Bottaccione, in Bottaccione Gorge, near Gubbio, Italy. It’s the nearest place for a coffee (1 €) while visiting a famous outcrop. Geologists who visit the gorge sign their names in the book.
Here’s my four-year-old geologist-in-training, etching his name into history:
We were led into the gorge by my friend and former student Alan Pitts (University of Camerino), who brought us to the outcrop that everyone travels there to see:
Here’s the outcrop from the other side of the road, and without Alan and me blocking the view. It’s squeezed in between the road and an aqueduct up the hill. Chain-link fencing covers the slopes above to retard the passage of falling rocks.
The reason this site is worth visiting? It’s the spot where the Cretaceous ends and the Paleogene begins, a major moment in Earth history preserved in a conformable stratigraphic sequence of pelagic limestones (the Scaglia Rossa). A thin seam of clay along the boundary (heavily etched out due to the intense interest of geotourists through the years) was found by Alvarez and Alvarez to be extraordinarily enriched in iridium, leading them to postulate an extraterrestrial impact hypothesis for the end-Cretaceous mass extinction event.
This thin seam is the geological “moment” that the ammonites died out, that the non-avian dinosaurs ceased existing, that the world switched from the Mesozoic to the Cenozoic. This clay seam is the end of an era, literally. It’s a profound moment in geologic time; a rough time for the global biosphere and a warning to those who survived.
It’s also a place where science changed: where the strict uniformitarianism of bygone years was replaced with a brasher, more violent “actualism,” that allowed one-off violent (“catastrophic”) events as major players in the evolution of the planet Earth. Team Alvarez changed the way geoscientists think about the nature of change in the Earth system; armed with compelling data, they pushed the boundaries of our imaginations. It was an inexpressible treat to be able to visit it last summer in person.
It’s not a gorgeous place. Signage alerting passers-by to the importance of the site is unfortunately in a pretty shabby state of repair:
Also, the outcrop has been heavily pockmarked with drill core sampling, leaving a ugly population of holes:
That said, I think anyone with the slightest interest in Earth history would be thrilled to put their hand on that crack between the strata, to contemplate the extraordinary shifts that took place there.
Here, the Littlest Stratigrapher and his stuffed wild boar toy approach the outcrop:
Visiting the K/Pg boundary at Gubbio perhaps meant more to our family than the average geo-family: My wife and I met on a dinosaur paleontology field course in Makoshika State Park, Montana, in the Hell Creek Formation and overlying Fort Union Formation. The boundary between the two? You guessed it: the K/Pg boundary, there marked by a coal seam containing some volcanic ash. We fell in love at the stratigraphic signal of the dinosaur’s demise, and here was an opportunity to revisit that same moment in geological time, in a different country, in a different depositional setting. And: we got to tote along our son this time – in a way for him, it is a sort of homecoming. He likely wouldn’t exist if it weren’t for our particular history with this particular stratigraphic interval.
…And so: this image is going on my family’s Christmas card this year:
“Happy holidays from the dawn of the Cenozoic, from the most extraordinary moment in the past 250 million years!”