30 July 2015
My favorite place to have lunch in Montana is at the Grinnell Glacier cirque in Glacier National Park. This is the dining room table:
You’re looking at a bedding-plane-parallel exposure of Mesoproterozoic stromatolites here. Every few years, I’m lucky enough to hike up there with motivated students and share food atop this unparalleled view into the shallow seas of more than a billion years ago.
Stromatolites are sedimentary structures that preserve the bulbous forms of ancient microbial mats.
The biofilm was probably photosynthetic, as the stromatolites domed upward toward the sun. You’re seeing them sectioned here like a head of cabbage sliced laterally through its ‘equator’… hence the middle of each of these concentric circles represents the oldest part of each stromatolite, and the outermost layers represent the most recent laminations to be tacked on before burial.
On the hike down from lunch, my students and I also saw some stromatolites sectioned vertically – so this is a different view, a side view, of the same dome-like structure:
These structures formed at a time when stromatolites were apparently the most advanced life on Earth. This planet was “Slimeworld” in the Mesoproterozoic, to use Gabrielle Walker’s memorable phrase.
Here, I positioned the students so each had stromatolitic laminations draped over the tops of their heads:
A stromatolite of a different color, seen in float below the cirque:
One more beast: a big erratic (note the glacial striations) full of stromatolites. Jake gives it a hug:
…And two close-ups of this boulder:
…Delicious repast for those who like nibbling on our planet’s Slimeworld past!
Glad you could join me for lunch.