Return to the Great Paleozoic Sea

Tiktaalik, what were you thinking?! Zina Deretsky, NSF.

In the midst of planning a tour of Paleozoic time in the Great Basin—a way to escape from this confusing disturbing world—I learned that thousands of people share my feelings. Amazing! What made the Paleozoic so alluring? It was a fish, specifically a charismatic fish that ventured onto land 375 million years ago. Tiktaalik (tic-TAH-lick) and its brethren are the progenitors of amphibians, reptiles, birds, and mammals. Yes, it was wandering fish—our ancestor—that got us into this mess!

Urban legend has it that Tiktaalik lived in a late Devonian paradise. The climate was mild. Stream banks, swamps, and other places where water met land were lush with delicious nutritious plants. Life was good. There was no reason to go back to the sea, at least not yet.

But life wasn't perfect. These early tretrapods most likely were stumblers rather than walkers. It probably took them all day to find enough food, and they could not escape predators. But as one paleontologist pointed out, Tiktaalik and its brethren were not burdened with self-awareness. “Everyone is, like, only barely conscious of the idea that they’re alive.” (Ben Otoo, U. Chicago grad student)

Now the Earth is occupied by creatures greatly burdened with self-awareness. Memers rage that Tiktaalik should have stayed in the ocean, thereby saving us all. Maybe those folks should return to the Paleozoic sea themselves. That's what I plan to do.

In the "desert ranges which lie to the west as far as longitude 117° 30' there is no considerable mountain body without its exposure of Palaeozoic strata" (geologist Clarence King, 1878).

Today's Great Basin is rich in remnants of the Paleozoic sea that covered much of today's Nevada and Utah. That sea was born about 700 million years ago, when the supercontinent Rodinea was breaking up. The former west half of Nevada drifted away, leaving the eastern part and adjacent Utah underwater. This was a passive continental margin, on a single tectonic plate. There was no tectonic jostling, only geological serenity (DeCourten 2003). Tens of thousands of feet of sediment accumulated on the sinking ocean floor.

Driving across northern Utah and Nevada, you can't miss the remains of that great sea. Most mountain ranges include or are even dominated by Paleozoic strata. Guidebooks make clear that this is not a monotonous stack of rock. There are nearshore carbonates in the east, and deep water siliceous rocks to the west. Quartzites tell of massive sand floods, beds of dolomite force us to confront the mysterious "dolomite problem", and there are fossils galore.

House Range in western Utah, a monstrous tilted stack of Cambrian rock; view from west, October 2021.

Lone Mountain near Eureka, Nevada, May 2021. Click to view Eureka quartzite (arrow), product of sand floods; other strata include limestone, dolomite, and shale (DeCourten & Biggar 2017).

Steeply-tilted Permian conglomerate at Tyron Gap; sediments were eroded off the now-gone Antler highland. Sulphur Springs Range, Nevada, May 2021.

Limestone and dolomite from late Devonian time, when Tiktaalik was venturing ashore; Devils Gate west of Eureka, Nevada, May, 2021.

Maybe on this trip I will find the perfect outcrop where I can rest peacefully and imagine myself in the warm shallow waters of that great Paleozoic sea, only barely conscious of being alive. This is not a childish pursuit. For all of us, pretending can make the world more magical and meaningful (Scott Hershovitz).

Sources

DeCourten, F. 2003. The Broken Land: adventures in Great Basin geology. U. Utah Press.

DeCourten, F, and Biggar, N. 2017. Roadside Geology of Nevada. Mountain Press.

Imbler, S. 2022 (Apr 29). "Started Out as a Fish. How Did It End Up Like This?" New York Times.

King, C. 1878. Systematic geology. Report of the geological exploration of the fortieth parallel, v. II. GPO.

Spring has arrived in the Laramie Mountains :)

I have good news! When I visited the trees I'm following this year—a balsam poplar and a quaking aspen in the Laramie Mountains—I found persistent snow but also many signs of spring. It was so nice to see the area coming alive. Made me feel more alive myself!

At my height, the two trees showed no signs of change.

Populus tremuloides left, Populus balsamifera right.

High above, the aspen was in full bloom. The poplar was still dormant, which is normal for that species.

Aspen canopy covered in catkins.

Poplar canopy with just a few dead leaves.

The aspen flowers were much too far away to examine, so I checked other trees nearby. Those with catkins within reach revealed themselves to be male (quaking aspen are dioecious).

Aspen tree in full bloom.

Catkin of male flowers; click to view dark pink anthers.

Aspen grow in clones, which can be huge. Can I assume the trees in this area are a single clone and therefore my tree is male? I don't know. We'll let the mystery be.

Aspen with green photosynthetic bark were common, but occurred in groups. Some clusters were obviously green, others were nearly white. As I mentioned last month, there's a theory out that aspen bark is thin because dead cells are shed each year, forming a powder on the surface. I tested several trunks, rubbing my finger on the bark, and decided ... well ... maybe.

The scouring rushes (Equisetum) along Pole Creek near my trees are much greener now—time to get busy with photosynthesis! Several had young cones.

Click to view equisetum cones mid photo and upper right.

The brown scales of the cone have sporangia on their lower surface, which will mature to release spores.

There was another nice surprise close by—a patch of pink wintergreen, Pyrola asarifolia.

Leathery evergreen leaves.

Last year's capsules with persistent curved styles.

For more tree-following news, have a look at this site, kindly hosted by The Squirrelbasket. If you'd like to join us, see the information here (it's really easy :).