July 4 at The Great Unconformity
Steve approaches a great flat rock where guitars are tuning up
outdoors.159.83: (gail)
Midday we came to Blacktail Canyon, and stopped at the hot sandy beach
for a walk. We followed a little trail up over the rise and down into
a deep dry canyon, an astounding narrows through the shelfy Tapeats
sandstone, resting here on the ancient schist below. The Tapeats makes
slot canyons with shady ceilings because of the layering in the beds.
Above us in places the canyon had been narrower than it is now, and it
had the feel of a twisting hall with a skylight running the length of
it, curving for elegance.
Lanky Danny and super-hiker Elena set a pace, and we all strung out
behind. At the end of the canyon we were stopped by a pool of muddy
looking water with a smooth dry fall above. We turned back down the
shady slot canyon and came upon a widening, with a large rock slab like
a stage in the middle of the sandy canyon-bottom. A little trickly
yellow light showed on one of the walls, but the light was mostly
indirect and rosy.
Shawn, Factor and Sam had brought their guitars, and were tuning
seriously with some sort of high-tech tuning fork gismo. We settled
down around them, and enjoyed a concert of local folk tunes and
singers' favorites. One of the passengers requested "This Land Is Your
Land" in honor of fourth of July, which it was, but the guitar players
didn't know it, and none of us had quite enough lyrics to pull off an a
capella rendition. We had a song about geologic time instead, and some
assorted love songs, over which to lay our remembrances of American
history and fortune.
Then Elena pointed out the actual contact between the strongly layered
Tapeats Sandstone, the dark tan colored rocks arching above us, and
some charcoal colored schist. Over a billion years missing. In the
Tapeats one sometimes might find sea worm-burrows or impressions of
trilobites' resting places. Astounding to contemplate. This in spite
of the fact that Tapeats was wave-swept, a sandy area offshore from
beaches, not the most conducive to fossilization of rocks of that
era. The Cambrian time, the time when those waves were layering this
sand, used to be thought of as the time of the beginning of life on the
planet in the classic days of geology last century, when the science
was first established. Comparing fossils and the sequences of layers
exposed in different places was the beginning of deciphering a history
of the earth. Below the Cambrian period (since placed at 570 to 245
million years ago by modern dating methods), was lifeless rock, with no
fossils to be found.
Turns out this was wrong. The sandstone above was home to worms and
invertebrates of various kinds, and the older schist below the contact
and under our feet had been home to life during a far earlier
revolution. Just before this older sea-bottom was laid down to become
siltstone, since almost remelted in high pressure metamorphosis into
shiny schist, the unicellular, anaerobic life forms found in
microfossils of this age had developed chlorophyll. And they had begun
to influence that anaerobic atmosphere, causing a widespread extinction
of earlier forms, and the beginning of multicellular evolution. All about
1.7 billion years ago.
This was the Great Unconformity as it is called, making a stripe of two
rock types at eye-level in Blacktail Canyon. I placed my palms on the
stone, lapping a billion-plus year gap in the fossil record at this
place on the earth. Had to laugh to think of Nixon's erasure compared
to this gap in the record on the wall. What triumphs and atrocites were
lost to us forever?
In between my hands, mountains had been uplifted and eroded away, maybe
more than once. And an oxygen atmosphere eventually came to be. The
sheer incomprehensible wonder of it... what a satisfying moment of
awe, what a temple of time.
Made a fine concert hall, too.
I hope to keep expanding this story and site, so please check back later...
thanks for reading!
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