Blast From The Past! — Part 3
Opening of the "BLAST FROM THE PAST" exhibit, June 1997
Interview with Dr. Brian Huber
Ocean Drilling Program Leg 171B was designed to recover a series of 'critical boundaries' in Earth history in which abrupt changes in climate and oceanography coincide with often drastic changes in the Earth's biota. Some of these events such as the Cretaceous-Paleogene (K-T) extinction and the late Eocene tektite layers are associated with the impacts of extraterrestrial objects, like asteroids or comets, whereas other events, including the benthic foraminifer extinction in the late Paleocene and the mid Maastrichtian extinction events, are probably related to intrinsic features of the Earth's climate system. Two of the critical boundaries, the early Eocene and the late Albian, are intervals of unusually warm climatic conditions when the Earth is thought to have experienced such extreme warmth that the episodes are so Dr. Huber is a micropaleontologist from the National Museum of Natural History and member of the Ocean Drilling Program expedition team that recovered the deep-sea core featured in the exhibit.
What events led to the discovery of this core?
Dr. Brian Huber: The ocean drilling program expedition involved a transect of sites 300 to 350 miles east of north Florida. Dr. Richard Norris, from the Woods Hole Oceanographic Institution, charted the course, anticipating that a well-preserved Cretaceous/Tertiary (K/T) boundary would be cored at one or more sites in that area.
During the drilling, we could tell, based on microfossil ages, that the drill had reached a depth about one core away from the K/T boundary, so several of us gathered on the deck to watch as the next core was removed from the drill pipe. When the core was laid out on the deck we knew immediately that we had hit the motherlode; we could see the distinctive changes in sediment color and texture that are characteristic of the K/T impact event. We had even more to celebrate when we drilled two more holes at the same site and recovered equally well-preserved and complete K/T boundary sections.
What does the core show?
Huber: The color change in the sediment is very dramatic. It goes from white Cretaceous chalk in the lower portion of the core, to a dark gray, coarse-grained layer in the middle that contains tektites (material ejected from the impact site), to gray-to-white Tertiary muddy chalk in the upper portion. When the core was split for sampling, we could see the very thin, rust-colored iron-rich layer, known as the fireball layer, at the top of the tektite layer. This rust layer, which has been found at a number of complete K/T impact horizons worldwide, contains particles of the asteroid and fine soot and ash that rained down on Earth's surface after the collision. I analyzed microscopic fossils called foraminifera from core scrapings and verified that the K/T boundary was, in fact, complete. The microfossil preservation in the core is excellent. Tertiary foraminifera are very different from Cretaceous species, as 90 percent of the Cretaceous foraminifera suffered extinction. Cretaceous species are much more diverse and include creatures with much larger and more ornate shells than Tertiary species, all of which makes looking at foraminifera an excellent way to identify this moment in geologic history.
What is the connection between this core sample and the dinosaur extinction?
Huber: We know, based on the age of the core and the age of the dinosaur extinction, that the impact event and the extinction occurred at the same time. By studying the deep-sea core in detail we will learn a great deal about catastrophic changes in the environment that occurred as a result of the impact. We hope that research will help us understand why the dinosaurs and many other organisms were wiped out, and why many other groups of organisms survived.
Why is this an important exhibit?
Huber: There's just nothing like looking at real objects that convey fascinating insights into other cultures, ancient organisms, or dramatic events in Earth's history. This exhibit represents a unique opportunity for visitors to see sediments that tell the story of the asteroid impact and the extinctions that followed. It's tremendously exciting to be able to interpret this record of the moment when a 10-kilometer-wide asteroid slammed into Earth and imagine the incredible force of the impact, and the wind, searing heat, and towering tsunami it created. This cataclysm profoundly changed the course of evolution. If it hadn't happened, in all likelihood we wouldn't be here today.
What will visitors experience when viewing the exhibit?
Huber: I think they'll get a sense of awe at the magnitude of the collision and its aftermath. An exhibit mural by Museum artist Mary Parrish illustrates the drama of the moment the asteroid struck. A huge cloud of ejected earth and rock races northward opposite the angle of impact. A white-hot vapor cloud billowed out from the 180-kilometer crater. And a shock wave expands outward from ground zero.
Also, the exhibit conveys that the dinosaurs weren't the only things to go extinct. Magnified photographs of pre-impact and post-impact foraminifera show that even these single-celled microorganisms suffered almost complete extinction. We hope, too, that the 15-centimeter-thick tektite layer, deposited over a period of days to months immediately after impact, will give visitors a sense of the enormous quantity of material blasted into the atmosphere; in contrast, the sediment before the tektite layer and after the fireball layer accumulated over tens of thousands of years, as fossil microorganisms settled on the ocean floor.
Finally, Mary Parrish's landscape of the post-extinction nuclear winter depicts the skeleton of a Triceratops and, in the foreground, young ferns and a pair of small mammals. This image of life re-emerging after the terrible event conveys the resilience of nature. Some animals and plants survived, and new groups evolved. Yet the cast of characters who made it and those who didn't could not have been predicted.
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