Understanding the mechanisms of environmental change caused by extraterrestrial impact events

What caused the extinction of the dinosaurs? The first thing that might come to mind is a meteorite hitting the Earth. Assistant Professor Honami Sato, a geologist at the Faculty of Science, studies impact-derived deposits to understand the mechanisms of environmental change on the Earth. We spoke with Sato about her research for the field work and also her fascination with geology.

The original Japanese version of the interview can be found here.

Discovering the Earth’s history through geological deposits

Could you tell us about your current research?

My fields of interest are geology and geochemistry. In particular, I conduct research that searches for evidence of extraterrestrial impact events in deposits in order to understand the mechanisms of environmental change caused by the impacts. An extraterrestrial impact event is just that—a phenomenon in which a meteorite strikes the surface of the Earth. Such impact events range in size from large events that may have caused the mass extinction to small events that have no effect on the Earth’s environment. In my research, I have focused on the large-scale extraterrestrial impacts.

How do you investigate the traces of these extraterrestrial impact events?

I visit sites in Japan and abroad to collect rock samples and conduct analyses in our lab. I mainly study geological deposits in Europe and the U.S.

My main research targets are samples deposited between three billion years ago and 66 million years ago, which is when the dinosaurs became extinct. I often go to Europe because it has deposits from about 200 million years ago that are still in very good condition.

That sounds like a tough environment to your fieldwork.

In many cases, a field site is in the mountains and the trail is steep, so we need to be well-equipped. On the way up, my backpack is almost empty, which is fine, but on the way down I’m carrying a backpack full of rock samples, which makes that part of the hike really tough.

How do you figure out where the impact-derived deposits are?

Large-scale impacts create craters on the Earth’s surface, but craters are easily affected by erosion and disappear over time, limiting the scope of our research.
We work on the assumption that material scattered by the impact must have deposited and remained in the strata, so we use information from previous studies to identify and investigate strata of the same age as the crater formations.

How do you detect extraterrestrial material in your collected samples?

There are two methods. One is to use a microscope and look for spherical particles in the samples. These particles tend to have a rounded surface caused by melting under the heat of impact.

The second method focuses on highly siderophile elements such as osmium, iridium, and platinum, which are abundant in meteorites. Using high-precision analysis, we determine if highly siderophile elements are present in collected samples. If these elements are enriched in the samples, it likely indicates evidence of an impact.

With either method, it is difficult to determine if the rock contains the target material when we collect samples. This means that we have to keep repeating the process of collecting and observing a large number of samples.

The excitement of holding a piece of the history of the universe

How did you become interested in the field of geology?

When I was in high school, I wanted to study astronomy at university. When I got there, I started studying at the Faculty of Science, and one lecture I took was on detecting cosmic dust in strata. That sparked my interest in geology, allowing us to learn about past cosmic events through geology.

It sounds exciting to be able to capture the history of the universe.

Yes, it is. For my undergraduate thesis, I found geological evidence of a large-scale impact event in the sediments of Japan. It was exciting to discover the impact-derived sediment recorded as a thin layer of claystone along the Kiso River in Gifu Prefecture.

I think the great appeal of geology is the ability to discover extraterrestrial materials in strata—materials that once traveled through space to reach Earth—and to feel that you are holding the history of the universe in your hands.

What are some of your most memorable moments since becoming a researcher?

In 2016, I participated in an international project to drill into the Chicxulub crater, which was formed around the time that the dinosaurs became extinct. I felt emotional as we retrieved sediment from the seafloor and saw the thick, impact-derived sediments beneath a crater. It was a profound moment for me to realize that such an impact event had actually occurred and had left significant changes in the Earth's environment.

Focusing on sediments reveals hidden insights

What is unique about your laboratory?

I think our great strength is that we can study extraterrestrial materials in sediments, not from meteorites themselves. It is difficult to detect such records in sediments because these materials are diluted by the terrestrial materials, but in my lab we have refined our methods to make such detection possible.

Why do you study the impact-derived deposits rather than the meteorites themselves?

The study of geological strata allows us to obtain high-resolution temporal data. This allows us to observe in detail the environmental changes that have occurred across an impact-derived sediment. We can get information before and after the impact event by studying of these sediments in detail. That's why I think it's essential for in-depth studies of environmental changes.

Please tell us about the research for which you received the Commendation for Science and Technology by the Minister of Education, Culture, Sports, Science and Technology in 2023.

This research project was something I had been working on with my supervisor during PhD student and collaborators. We were trying to determine the influx of all kinds of extraterrestrial materials in sediments through geological time scale—everything from sub-millimeter cosmic dust particles to large impact events.

Large-scale impacts could have a huge effect on marine and terrestrial ecosystems. I think this research could be useful for predicting future changes in the Earth’s environment based on such cases from the past.

Sharing the excitement of geology with students

What do you try to keep in mind when teaching students?

I keep in mind that each student has a different area of interest. So, while I prepare some research topics for them, I consciously avoid making too many suggestions. Instead, I try to allow students to determine their own research directions and methods.

What kind of people do you want your students to become?

Even if students do not become researchers, I hope that they will always have an inquisitive mind about whatever work they do. I expect them to take pride in their work, to think proactively about what they can contribute, and to strive to add value in whatever they do.

What are your goals for the future?

My goal is to establish a laboratory specializing in extraterrestrial impact events. We can obtain many samples from sediments around the world that have been recorded in the Earth's history. I want to create a laboratory where students can come and do all kinds of research on impact events.

The extinction of the dinosaurs due to the extraterrestrial impact event is the most widely recognized theory. This research is widely understood by the general public, especially children, and is a good starting point for outreach. My hope is to provide opportunities for more people to learn about geology.

Finally, do you have any advice for high school students who are still deciding whether to pursue higher education?

Geology is a fascinating field that offers glimpses into the history of extraterrestrial events and is filled with romance. This field is often overlooked in high school, so I hope you will be interested in learning about geology in university because I think you will discover new things.

Universities provide an environment conducive to the study of any number of fields. I encourage you to discover what interests you and pursue it wholeheartedly.