One of the first things geologists learn about is the major extinction at the end of the Permian Period (and Paleozoic Era) 250 million years ago. 96 percent of all species died during that mass extinction.
Now geologists have discovered new evidence that may point to another extinction during the mid-Permian, 262 million years ago, just 12 million years before the major Permian-ending event. An April, 2015, Geologic Society of America (GSA) paper (Lead author David Bond) notes that the "Capitanian" saw the extinction of 87% of all brachiopod species.
The Capitanian was named 20 years ago based on research in tropical to sub-tropical areas in China and elsewhere and believed originally to be more localized. Newest research in northern Norway suggests that this extinction may actually be more global (though several dissenters have commented on the publication in the well-respected GSA paper).
Dr, Bond et al write that the Capitanian extinction was likely triggered by the eruption of the Emeishan Traps, located in the southwestern Chinese province of Sichuan. Volcanic eruptions release large amounts of carbon dioxide, causing ocean acidification. Seafloor oxygen depletion may also have played a role.
The major shift after the acidification and oxygen depletion was from domination of brachiopods to domination by bivalves after the Capitanian extinction:
Brachiopods and bivalves differ in the number of adducting muscles, the way they eat, in their very classification, and in the symmetry of their shells. The two shells of bivalves are mirror images of each other; they are not in brachiopods.
So, why were bivalves better suited than brachiopods for life after the Capitanian? Any guesses?
Shellfishly (and sleepily),
Steph
Cheese Imitates Geology: Thin Vegetable Ash Layer and Thin Iridium-Rich Clay Layer
There is a small, wicker cheese basket at my local grocery store filled with little snippets of cheeses--the ends of various imported wheels and logs. This one caught my eye:
I unwrapped it last night and found this written on the wrapper (just so you know I'm not making this up):
A hairline layer of vegetable ash?! Oh my.
Of course, the iridium-rich clay layer found at the boundary of the Cretaceous period (about 65 million years ago) with the overlying Paleogene sediments first documented by Luis and Walter Alvarez (shown below) in Italy, sprang to mind. The limestone layers beneath the red clay are full of numerous species of foraminifera (forams) and the thick limestone beds above contain only one foram species. In between is this iridium-rich later of clay. In Italy. In Germany. In the Netherlands. In the U.S. All over the world.
Iridium is a rare, silvery, white transition metal of the platinum family found in meteorites. It was named for the Greek goddess Iris after the rainbow colors in its salts and less than 3 tons a year are mined world-wide:
Iridium is associated with the massive K-Pg extinction including the non-flying dinosaurs and a huge, diverse, plant population. (The boundary was called the K-T boundary for Cretaceous-Tertiary when the Alvarezes discovered it. The International Stratigraphic Nomenclature Committee has recently deprecated the Tertiary Period though; it now must be called Paleogene.) [First Pluto is no longer a planet; now we can't call it the K-T boundary any more. Sigh...] And the likely location of the meteorite hitting the earth in the Gulf of Mexico is also well documented.
What strikes me (no pun intended, okay, maybe...) about naming conventions in geology and in all areas, actually, is the creativity and force in coming up with these descriptive terms. As Clementine says to Joel when talking about her newest hair color in the film Eternal Sunshine Sunshine of the Spotless Mind, "Naming hair colors. Somebody has that job. I want that job!"
Calling the thin layer of vegetables in the Humboldt Fog Cheese "Vegetable Ash" is truly inspired to this geologist and cheese eater.
Last week: puddingstones that look like pudding. This week: Cheese that looks like limestone layers with a hairline layer of ash. It doesn't get much better than that full circle.
Thanks for reading. I look forward to your comments, thoughts, and cheesy ideas.
Until then, "say cheese!" (And mean it).
Humboldtly yours,
Word Woman (aka Scientific "Vegetable Ash Layer" Steph)
