As her plane landed in Germany, Heather Jones felt a wave of anticipation. For the next three weeks, Jones, a doctoral student in geosciences at Penn State, would be lending her scientific expertise in micropaleontology to assist the first-ever research team to collect samples from the Chicxulub impact crater. The crater is the remains of the cataclysmic event — an asteroid 6 miles wide crashing into Earth — widely believed to have led to the extinction of dinosaurs 66 million years ago.

"It was pretty intense, but it was also exciting to look at samples that nobody had seen before," she said.

Tiny fossils helping to answer big questions about Earth's history

The team, funded by the International Ocean Discovery Program (IODP), traveled in April 2016 to the coast of Mexico's Yucatan Peninsula to collect their Earth samples. The team extracted pieces of the peak ring of the crater in hopes that a thorough analysis would allow them to understand more about the event that caused the extinction of nearly 75 percent of the world's species. The Chicxulub impact crater is the only crater on Earth that has an intact peak ring, yet it is submerged in water off the coast of Mexico.

From aboard a drilling rig, the team dug nearly half a mile below the ocean's floor, past sediment that had built up over tens of millions of years, to access the layer of rock and embedded fossils impacted by the impact.

Tim Bralower, professor of geosciences at Penn State and Jones' faculty adviser, served as scientific expert on the drilling rig. Jones became involved once the cores were sent to the IODP’s Bremen Core Repository in Germany.

Jones' main job was to apply her knowledge in micropaleontology, specifically the study of microscopic nannoplankton fossils, to help date the layers of the core. The core is a column of rock and sediment approximately one foot in diameter and more than 1,000 feet tall. As one piece, it would be nearly as tall as the Empire State Building, but the core was segmented, as it was extracted from the Earth, into 303 pieces. 

By examining each section of core for "marker species," Jones helped the team understand how far back in time they had drilled.

"Certain species of the fossil plankton, which we call marker taxa, tell you where you are in time, so you can create an age model," she said. "We look for the presence or absence of species that we know existed only during specific time periods. As soon as you see that the fossils for one of these species has disappeared, you know you're in a different time period."

Jones spent 11-12 hours each day for three and a half weeks looking through microscopes and analyzing the shapes and sizes of the plankton fossils. She and two colleagues formed the micropaleontology team, working alongside researchers from around the world who studied other aspects of the samples, such as the composition of the rock. The fossils were so small that Jones needed to use a microscope with a thousand-times magnification.

The team is seeking to answer a range of research questions, including how species adapt to cataclysmic changes. Their first paper, published on Nov. 18, outlines how craters are formed. This research demonstrated that the peak ring was underlain by igneous rock from deep in the Earth's crust overlying sedimentary rocks, implying that craters create vertical mixing between the different types of rock. This has implications for how land masses and oceans form and change over time.

A passion for fossils from an early age

Jones has had an interest in studying fossils for nearly her entire life. Growing up in England, she remembers visiting a science center in Wales that allowed children to dig for pretend fossils and assemble the pieces they found into the shape of a long-gone animal. That experience, as well as watching Indiana Jones movies, she said, piqued her interest in fossils. In high school, she learned about geology and enrolled in a dual B.S./M.S. degree in geology at Southampton University. 

Her master's adviser, Samantha Gibbs, Royal Society University Research Fellow at Southampton, got Jones involved in a project investigating nannoplankton fossils.

"She was so enthusiastic about her research and I found that I really loved doing this type of research, too, whether it was measuring the size of microfossils or describing or naming them. It's like a treasure hunt in a way," Jones said. 

Gibbs, before becoming a faculty member at Southampton University, had completed a postdoctoral fellowship at Penn State — with Bralower.

"Dr. Gibbs recommended that if I wanted to keep working in this research area that I get in touch with Dr. Bralower, so I did," said Jones. 

Jones began her Ph.D. studies in 2015, focusing on the same geologic event that led to the demise of dinosaurs, known as the Cretaceous-Tertiary, or KT, boundary. Nearly all nannoplankton went extinct after this event, but a few survived.

"In the Northern Hemisphere, we see an increased abundance of bloom species following the KT mass extinction. One species of these bloom species becomes dominant for several hundred thousand years before being replaced by another," she said. "This happens for about two million years after the KT boundary. My research investigates what causes these switches in dominant bloom species. I am looking at what environmental and/or ecological factors played a role."

Jones is collaborating with researchers at Yale University in her research and will be examining cores extracted from Tunisia, where there is a wealth of fossil data from the time period. 

Just like with the Chicxulub project, the focus of her work involves hunting for the presence or absence of microscopic fossils. Projects like the Chicxulub dig, she says, have confirmed her interest in micropaleontology and have boosted her confidence in a niche field that has the possibility to shed light on many unanswered questions about the Earth's past.

Now that she is back in the U.S., Jones is already looking for another major IODP research expedition that she could join, where she can lend her micropaleontology expertise.