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Searching for traces of the three-hundred-meter-high tsunami
Sixty-six million years ago, a gigantic meteorite over 10 km in diameter hit the earth. The area around the Yucatan Peninsula in Mexico, the point of impact, was instantly enveloped in a heat wave of 10,000 degrees Celsius. The blast and shock waves struck an area of 1,000 to 2,000 km around it, vaporizing, burning, destroying, and killing everything in its path. The tsunami generated reached a maximum height of three hundred meters. The impact launched countless pieces of rock so high that they left the atmosphere, only to return as balls of fire, heating it to three hundred degrees Celsius.
Scientists theorize that such an enormous meteorite impact event caused the extinction of the dinosaurs. As a student studying earth science at Tohoku University, Kazuhisa Goto learned about this theory of the Chicxulub impact event from a book he had by chance. He became interested in conducting research together with the author, the late Dr. Takafumi Matsui.
“It was fascinating, and I got really excited. Just when I thought I had found the kind of research I wanted to do, I learned that Professor Matsui was involved in a project at the University of Tokyo investigating impact events and their aftermaths on Earth. So, I came to the Graduate School of Science to join the project,” he says with nostalgia.
But there is more to the story of the giant meteorite. Let Goto himself elaborate.
“It was not just the impact itself but the changes that occurred on the planet afterward that played a crucial role in the extinction of the dinosaurs. First, the massive amount of dust spewed up by the impact blocked out sunlight. It used to be thought that some photosynthesis would have been possible. However, with the development of computational technology, new assessments suggest that Earth was almost completely dark for several years. It also cooled down, and global temperatures dropped by twenty degrees Celsius. Nowadays, there is great worry about climate change because a rise of even “only” 1.5 degrees Celsius has devastating effects. So, a decrease of twenty degrees meant extreme cold environments around the planet. Plants were dying because they could no longer photosynthesize. The herbivores were dying because there were no plants around to eat. And the dinosaurs at the top of the food chain could no longer survive. Our current understanding is that these conditions continued for about ten years after the meteorite impact.”
Despite these horrors, the flame of life was not extinguished, and recovery from this apocalyptic doom followed.
“In the food chain, animals such as rats and snails feed on animal carcasses and dead plant leaves. Even after the meteorite impact, these organisms continued to be supplied with food. This is how small mammals, the ancestors of humans, survived. After about five years, sunlight reached the earth and gradually warmed the atmosphere. Plants sprouted from the seeds buried underground, and the environment started to recover. I suspect the apocalyptic conditions were limited to the first few years.”
Goto says that the ability to more accurately describe the conditions sixty-six million years ago is largely due to advances in computer technology. There are also more precise calculations in many areas of research, such as climate simulations. What has been learned from studies of Earth in the past is often applied to the computational models of the present. For example, if a meteorite were to hit the planet tomorrow, it is possible to predict how much rock and dust it would whirl up. This means that, after all, research on the past is also research on the future.
“We try to decipher what happened in the distant past and how the planet and its organisms responded to it. By studying Earth's past, we may find the answers to the difficult question of how organisms will respond to the current climate crisis. I believe this is one of the roles and contributions of our research.”
Major role played in the debate about the Chicxulub impact event
The first foreign country Goto visited in his life was Cuba. Of course, it had something to do with the giant meteorite.
“Sixty-six million years ago, the Yucatan Peninsula was underwater. It is what was the seafloor at that time that rose and became the peninsula. Therefore, we can see on the surface the sediments that accumulated on the seafloor when the huge meteorite hit the planet. As such, I was taken on a geological survey in Cuba to study the sediments right after I entered graduate school. We would walk along trackless paths in the dense jungle, relying on old maps to find subtle changes in the strata.”
At the time of the meteorite impact, Earth’s climate was warm, and swarms of plankton inhabited the oceans. The whitish strata contain that plankton. After the meteorite impact, the plankton died, and the strata became reddish, with the mineral content dominating. The survey team spent many days searching for the strata where that color was changing from white to red. The boundaries of this strata contain traces of the meteorite impact.
“We were pushing our way through thick tropical vegetation to check the strata, only to come up empty-handed and have to go ever deeper in the jungle. It was very difficult to find a site. In the first year, we found several candidate sites. In the second year, we received permission from the Cuban government to take samples of the strata and brought them back to Japan for analysis. Then, in the third year, we collected different samples. Then we would repeat this cycle.”
Goto’s master's and doctoral dissertation topic was the Chicxulub impact event, but he focused on the tsunami that occurred following the collision.
“The perturbations in the sea would stir up the dust, sand, and other forms of soil that would later be deposited as sediment. Or at least that was the theory. I wanted to understand this process properly, so I decided to examine the traces of the tsunami after the meteorite impact. I theorized that we should be able to see in the strata that the bigger pieces fell back down first, followed by smaller pieces. I wanted to figure out whether the layering of the sediment could be evidence for the tsunami happening.”
Although the Chicxulub impact event theory is now accepted in geology, it has been the subject of a great debate, with arguments both for and against it. An important part of the debate was whether the tsunami deposits existed. In 2010, six years after the submission of Goto's dissertation, 46 researchers from around the world undertook the task of reevaluating the evidence for the theory. The group of scientists led by Professor Emeritus Takafumi Matsui and Goto was in charge of clarifying the circumstances of the tsunami immediately after the meteorite impact.
Earth is created by disasters
The 2004 Indian Ocean tsunami, which killed 240,000 people, brought Goto back from sixty-six million years ago to modernity.
“It was just my first year as a postdoctoral fellow. I couldn't imagine what the three-hundred-meter-high tsunami of the Chicxulub impact event was like. When I saw the images of the Indian Ocean tsunami that killed so many people and which was about thirty meters high, I was shocked. It finally sunk in that events like this do happen. It made me face the fact that such huge tsunamis must have happened frequently in the past and are bound to happen again in the near future. I realized the importance of studying the geology and history of tsunamis, and I immediately flew to Thailand and Sri Lanka to begin my research.”
Only seven years later, the Great East Japan Earthquake struck.
“I knew there was a high possibility of it happening. Still, I did not, or could not, imagine that an earthquake of a once-in-a-thousand-year scale would happen in my lifetime.”
Of course, Goto also conducted research on that tsunami as well. He points to the striped layers of iron-rich and iron-poor strata of a meter-long geological sample (core sample) collected in and around Sendai after the earthquake, now kept in his laboratory.
“Here (at the top of the geological sample) is the surface of the ground after the 2011 tsunami. Below that is the paddy soil that was there at the time. The yellow area below that is dated to 1611. This was around the time Date Masamune founded the Sendai Domain. The tsunami hit shortly after, and traces of it can be seen here. The white, smooth area further down is the volcanic ash from the eruption of Lake Towada in Aomori Prefecture in 915. Lake Towada was actually a huge volcano. At the bottom are the traces of the great tsunami caused by the Jogan Sanriku Earthquake in 869. More than a thousand years of history is packed into a sample only one meter long. What is more surprising is that more than half of this sample accumulated instantly after a disaster. In other words, we live on top of the sediments accumulated by disasters.”
However, Goto adds that “disasters” is a word reflecting the human point of view. From the planet’s point of view, disasters are merely “natural phenomena.” Nature is merely following its “natural” path.
“We live in the anthroposphere, the sphere of humans. And it is getting bigger and bigger, increasing our contact with nature. We experience this as climate change, environmental problems, or natural disasters. I would like to treat “disasters” and “natural phenomena” separately and understand “natural phenomena” themselves. I believe that this strategy will ultimately lead to preventing disasters.”
In other words, we can examine “disasters” more macroscopically and accurately by perceiving phenomena from “nature’s point of view” rather than from “humanity's point of view.”
Interest in the processes of destruction and regeneration
Mangrove forests, coral reefs, and the distant planet Mars are all subjects of Goto's research, dedicated to examining “disasters” and the “regeneration” that follows.
“The Indian Ocean tsunami devastated mangrove forests in Thailand and Sri Lanka, but these devastated mangrove forests will probably regenerate. What exactly determines how they can regenerate? Biological factors, the shape of the terrain, and the types of soil may all play a role. The same applies to the destruction and regeneration of coral reefs. Studies have shown that the coral reefs of Ishigaki Island are also hit by large tsunamis once every two hundred to three hundred years. I am very interested in the processes of destruction and regeneration, both the mangrove forests and coral reefs, processes similar to how Earth regenerated after the destruction of the giant meteorite, but on a more local scale. When there is an influence at such a scale, everything is devastated, and the planet resets and regenerates. However, it might regenerate to the state it had been in previously, or it might be reborn in a completely different state. What determines which version is realized? That is what I want to know.”
Research on Mars is also "part of understanding better Earth's history," Goto says. He has been focusing on the South Pacific region, including Fiji, Tonga, and French Polynesia. It is an interdisciplinary project involving researchers from different fields, such as archaeology, ethnography, and engineering.
“People have been inhabiting the islands of Polynesia for 3300 years, the flourishing Lapita culture is one example. In the 16th century, the Age of Discovery brought Europeans to the islands, so we have written records from that time onward. However, even before we had written records of the region, indigenous people had moved around to various islands several times. What triggered these migrations? Major disasters may have been behind these milestones. One of them could have been the giant volcanic eruption in Vanuatu in the fifteenth century, said to be the largest eruption of the last ten thousand years. A huge tsunami also occurred at that time. There are many other stories in mythology and folklore that sound like stories about giant tsunamis. I would like to reveal the history of volcanoes and tsunamis from the geological strata to find traces of such prehistoric catastrophes and to find out if the legends are correct. I want to illuminate the three histories simultaneously: the history of disasters in Polynesia, the history of humanity, and the history of environmental changes. I have just begun this work.”
In this ongoing project, Goto travels to Polynesia twice a year to conduct fieldwork. He laughs as he describes his work in the jungle as hard but "fun is waiting on the other side.” Goto has a bookshelf in his room at home, where he keeps his personal belongings and work clothes instead of books so that he is always ready to go out to do fieldwork.
Focus on your interests
Goto says that earth science is fun because you can change the scale of your perspective in time and space at will.
“We can simultaneously talk about an event at a scale of “once every hundred million years,” and its direct aftermath that lasted merely a minute, as in the case of the impact of the giant meteorite sixty-six million years ago. We can talk about the entire planet, and we can also talk about local events in Tokyo. In other words, we can freely manipulate the scale of space and time and go to the past or the future. That is one of the joys of earth science.”
What can be seen from such a flexible and versatile point of view? Goto believes that there must be something useful for the future of humanity.
“I think humans are probably the first creatures to understand that they influence the planet. Other organisms have also changed the environment but without understanding their own impact. For example, cyanobacteria and phytoplankton transformed the ancient Earth from a planet with almost no oxygen into a planet with plenty of oxygen, which was tremendous environmental pollution at the time. However, this triggered the subsequent evolution of living organisms. With that in mind, it is very difficult to define the present era. The planet will probably continue to exist no matter what happens. However, for human civilization to continue to prosper, it is vital to find a way to coexist well with other living organisms. To do this, it is crucial to know and understand how Earth has changed over the millennia. This, I believe, will help us to find the path that we should take. Knowledge learned from the past helps us imagine the future. In that sense, I think it is one of the duties of earth science and consequently a duty of mine, to tell the story of the past and talk about what the future might look like.”
Ever since he was a boy, Goto was fascinated by the origins and decline of civilizations and felt drawn to archaeology. However, “career guidance automatically placed me in a high school science and mathematics class, and it was there that I first learned that archaeology was a humanities subject,” he laughs and continues.
“I thought “Well, this is unfortunate.” But then I learned that, when studying the Egyptian civilization, a geological approach was taken to estimate when the sphinx was made based on the origin of and erosion marks on the stones it was made of. So, I felt like studying geology might be a good idea after all."
Based on his own experience, Goto offers the following advice to young people.
“I think you have to focus on what you are interested in. The field of study, for example, might follow as a result, but not necessarily. It would not have been surprising at all if I ended up in a humanities department. I also spent about five years in an engineering department during my career. I think that as long as you have solid interests, you can find opportunities in a variety of places. That way, you can have fun and keep moving forward. By the way, if you join my laboratory, you can travel to various places around the world. You can even do interdisciplinary research that combines the humanities and the sciences (laughs).”
When asked about his ultimate goal, Goto replies as follows.
“I have not thought about it much. If I could add a few lines of knowledge I learned through research to the book of humanity’s history, I'd be happy with that.”
※Year of interview:2023
Interview/Text: OTA Minoru
Photography: KAIZUKA Junichi
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