What I Hope to Learn From Exp. 364

I love what I do, but I’m not just out here for fun. This is big science, and everyone on the science party is working hard to advance our fields of study in important ways. I’m a micropaleontologist, and, more broadly, a paleoceanographer. I study a group of hard-shelled marine protists called foraminifera to understand how the ocean changed in the past, and how marine life responded to those changes. This is interesting in and of itself, and is also hugely useful when trying to understand how future climate change might affect the world ocean.

On IODP Exp. 364, I have two main tasks. The first is to tell the age of the rocks, both on the rig as the come on deck, and then in more detail after the onshore science party in Bremen. The Geologic Time Scale is and always has been based on the occurrence of different fossil species in different rocks. Early geologists found a particular group of fossils in Devon, England; when they found them elsewhere they called those rocks “Devonian.” They found a different group of fossils in the Jura Mountains of Germany and called other rocks with those fossils in them “Jurassic,” and so on. In the 200+ years since this early geologic time scale, we’ve been steadily refining this time scale to smaller and smaller increments. More recently we’ve gained the ability to use the radioactive decay of natural minerals to assign numerical ages to different periods (the Cretaceous goes from 145-66 million years ago, for example), but the boundaries of these lengths of time are still mostly defined by fossils.

Marine microfossils like foraminifera are hugely useful for dating sedimentary rocks. They are widespread in the world’s oceans, and hundreds to thousands can be found in a few cubic centimeters of sediment. We also know the ranges of individual species very well, largely due to the 40+ years of scientific ocean drilling by the IODP and its predecessor programs. Given this large amount of data, we can say with confidence that species A goes extinct at a certain point in time, and species B first appears at a different, younger point in time. So when we’re taking cores, going down through layers of sediments, we’ll see species B first, and as we go deeper into older and older sediments, eventually we’ll reach a point where species B first evolved, and then (from our perspective of going backwards in time) it will disappear and we won’t see it anymore in older samples. Then as we continue going deeper, eventually we will come to the point where species A went extinct, and then we will begin seeing it in our samples. Both of those “datums,” as we call them, are useful. When a species disappears and when a species first appears in our samples are important events, and we can often assign an age to them. So as we drill this borehole we can watch time go by and see how close we are getting to the boundary. This is an exciting process to experience in real time, to see new cores coming on deck and getting new samples under the microscope to see what the age is. It can lead to some big surprises, and has made my time offshore on the Myrtle a lot of fun.

On a broader scale, in collaboration with other members of the science party, I plan to study how life recovered from the last major extinction in Earth History. More than 75% of species on the planet went extinct at the end of the Cretaceous, including over 90% of planktic foraminifera, which live in the upper few hundred meters of the ocean. Interestingly, benthic foraminifera, which live on the seafloor, did not suffer a mass extinction. (This suggests that the environmental change that caused the extinction was too fast to effect the deep ocean; this has always been one of the strongest pieces of evidence for an impact-driven extinction). Only a handful of planktic foraminiferal species survived the end Cretaceous mass extinction, and two of them gave rise to new lineages that diversified rapidly in the tens of thousands of years immediately following the extinction event. In the immediate aftermath of the impact the Chicxulub Crater was a big hole that would have rapidly (in a geologic sense) filled with sediments that, hopefully, preserve an expanded record of these survivor species and their immediate descendants. I hope that this will prove a good place to study the early diversification of the surviving foraminifera and the environmental mechanisms driving it.

Chris Lowery

Featured Image: ELeBer@ECORD_IODP

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