A “Written in Stone” Photo is the Chapter 7 - Opener for a New Book on Extinctions

I’m pleased to announce that one of my photos from “Written in Stone…seen through my lens” is the Chapter Seven-opener for a new book entitled The Great Extinctions: What Causes Them and How They Shape Life by Norman MacLeod, Keeper of Palaeontology (the British spelling) of the Natural History Museum, London.

The photo is of a spectacular outcrop of the Champlain thrust fault at Lone Rock Point associated with the Taconic orogeny located in the northwestern corner of Vermont. You can visit my post on the subject here.

Of the 1-3 billion species estimated to have appeared during Earth's history, only 12.5 million exist today. Geologists know that species extinction is as natural a process as species evolution. They also know that the rate of extinction in the geological past has not been constant. On at least five occasions in Earth's history, extinction intensities have spiked well above the normal level.

For over a century, geologists have tried to conclusively identify and understand the processes responsible for the complex, fluctuating history of species extinction through the millennia. This has become even more important over the last decade as human populations and technology may now rival sea-level change, volcanic eruptions and asteroid impacts as an extinction mechanism. Will there be a sixth extinction? If so, then when? What will cause it? What life forms will succumb?

The Great Extinctions explores the history of this search, its subjects, its controversies, its current conclusions, and their implications for our efforts to preserve Earth's biodiversity. It explains what extinction is, what causes it and whether it is preventable, and by comparing past geological extinction events, it aims to predict what will happen in the future.

Chapter 7 deals with the End-Ordovician extinctions about 440 to 450 million years ago. The Ordovician Period was an era of extensive diversification and radiation of numerous marine clades. The event is cited as the second most devastating extinction to marine communities in earth history, causing the disappearance of one third of all brachiopods and bryozoan families as well as numerous groups of conodonts, trilobites and graptolites. In addition, much of the reef-building fauna was decimated. In total, more than one hundred families of marine invertebrates perished in this extinction.

Its cause is hypothesized to be related to South Polar glaciation in association with the austral locale of the megacontinent of Gondwana. The driving agents for the extinction are thought to be global climate cooling and the lowering of sea level worldwide.