August 20, 2012
Home sweet sweltering Los Angeles! The national heat wave is jarring, but the long hot nights are a relief after the Andean cold. Last week I was sleeping in a wool scarf!
We’re back in Los Angeles but the hunt isn’t over. We managed to bring back 2 duffle bags full of rocks – rocks that I have a hunch contain fossilized sponges.
Soft-bodied seafloor sponges rarely leave fossils. Typically, their bodies decompose, and if we’re lucky, tiny glass needles that once supported the porous sponge framework are later found among sand and mud particles in sedimentary rocks. From looking at microscope slides of Dr. Rosas, I know plenty of sponges inhabited the shallow seas along Pangea right after the mass extinction. But why does that matter?
Around 201,300,000 years ago, Pangea split open, releasing 10 million square kilometers of Hawaii-style lavarock (basalt). (Part of that spill is now the Pallisades near New York City!) Consequent changes in chemistry and climate correspond with the effects from human fossil fuel use we see today – and, at the end of the Triassic period – to animal extinctions around the globe. The aftermath of these events is most interesting too me, and the Triassic/Jurassic crisis caused fascinating changes. Dinosaurs radiated into suddenly available ecological niches, spreading to famously dominate the land. But in the sea?
Mass extinctions change everything. Even the least-significant animals build together frameworks and habitats and communities that shape our world. When those animals die the habitats – down to the very floor of the ocean – change dramatically.
In fossil hunts for my dissertation research, I’ve uncovered a mountain of unexpected sponges in Nevada. After the mass extinction, siliceous sponges dominated seafloor habitats here in seaways along the northern part of the Pangea supercontinent. I’m not talking about hundreds of sponges. I found millions of sponges, sponges that cover whole fossilized sea-beds, greedy sponges that apparently did not share well with others. We don’t see corals, clams, crinoids – all the other characters we’d expect to find. For about two million years the regular habitats – reefs, clam beds, crinoid banks – were missing
I traveled to Peru to compare and contrast the record from Pangea’s southern coast to what I’ve seen in Nevada. We didn’t know what to expect – maybe enough observations for a paper now, or maybe we’d scout rocks to revisit later.
We won the fossil lottery. We found both enough material to write a paper now, and so many excitingly challenging rock sequences and fossil occurrences that I’ve got to return to Peru next year!
The rocks we visited in Peru are incredibly well studied. In the western Andes they bear valuable metal ore and in the east they bear oil. Researchers in Peru want to know why the valuable materials occur. In the photo above, the head geologist for Pan American indicates the mountains, lakes, mine sites, and rock layers of animal history that link them all. I think this mass extinction, and the record animals that benefitted in its disastrous wake – holds the answers. The fossils and rocks we observed in the field support my interpretation that extinction-related changes in sea floor habitats caused the deposition of now-valuable human resources.
Now that I’m back at USC, we start a new search. I need to further test my interpretations by scrutinizing the microscopic record hidden in the rocks themselves.
I’ll start by making microscope slides from the rocks samples we brought home. To do this, I:
cut a domino-sized rock sample,
glue it to a piece of glass,
cut off the extra rock,
then polish the remaining sliver of rock attached to the glass ‘til it’s thin enough to see through.
Did I mention the glue has to be 140 degrees to seal properly? Yikes! Making these slides is no joke. But I’m so eager to see what’s inside these rocks! From microscope slides I made from Nevada specimens, I can now tell the difference between seafloor muck with bits of dead sponges, and rocks that contain actual fossilized pieces of sponges that died abruptly. I’ll use the microscopic observations to piece together how abundant sponges were, what habitat they preferred, and how much they hogged their territory.
I’ll post about what I find, but it may have to wait ‘til after we take the new USC Earth Science grad students camping this weekend! If this is your first visit to the blog, check out posts from our Andean Fossil Hunt – it was a wild adventure, and I can’t wait to go back!