Aurelia Butler

Although we can’t see it in action, the Earth is constantly churning out new land. This takes place at subduction zones, where tectonic plates crush against each other and in the process plow up chains of volcanos that magma can rise through. Some of this magma does not spew out, but instead mixes and morphs just below the surface. It then crystallizes as new continental crust, in the form of a mountain range.
Scientists have thought that the Earth’s mountain ranges are formed through this process over many millions of years. But MIT geologists have now found that the planet can generate new land far more quickly than previously thought.
In a paper published in the journal Geology, the team shows that parts of the Sierra Nevada mountain range in California rose up surprisingly fast, over a period of just 1.39 million years — more than twice as fast as expected for the region. The researchers attribute the rapid formation of land to a massive flare-up of magma.
“The really exciting thing about our findings is, with new high-precision geochronology, we were able to date how quickly that crust-building process happened, and we showed that this large volume of new crust was emplaced at an extremely rapid rate,” says the study’s lead author Benjamin Klein PhD ’19, who carried out the research as a graduate student in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS). “It was sort of an instant. It was a little over 1 million years, but in geologic times, it was super fast.”
Klein’s co-authors are Associate Professor Oliver Jagoutz and Research Scientist Jahandar Ramezani, both in EAPS.
A complete cross-section
The Sierra Nevada mountain range is a product of the collision of two tectonic plates: the westward-moving North American Plate and what at the time was the Farallon Plate, which ground slowly under the North American Plate, eventually sliding entirely into the Earth’s mantle.
Around 100 million years ago, as both plates collided, they created first a chain of volcanos, then a towering mountain range that is today the Sierra Nevada.
“What is today the West Coast of the United States probably looked, back then, like the Andes today, with high elevations and a chain of large volcanos,” Klein says.
For their study, the researchers concentrated on a geologic feature in the Sierra Nevada known as an intrusive suite — a large volume of rock that originally formed deep in the Earth’s interior. Once crystallized, the rocks form a new, vertical column of continental crust.
They focused in particular on the Bear Valley Intrusive Suite, a unique formation in that it represents the vestiges of new continental crust that is today exposed on the surface, as a 40-mile stretch of granite. These rocks, which today lie horizontally along the mountain range, originally formed as a vertical column. Over time, this tower of new continental crust eroded, stretching and tilting into its current horizontal configuration.
“The Bear Valley Intrusive Suite gives us a complete cross-section of what these magma plumbing systems underlying large volcanos looked like, where normally we would have a limited snapshot,” Klein says. “That allows us to think much more completely about how quickly new crust was being built.”
A speed limit for new crust
The team collected rock samples across a region of the Sierra Nevada Batholith and brought them back to MIT to analyze their composition. They were able to determine the age of nine samples, using uranium-lead geochronology, a high-precision dating technique pioneered by the late MIT Professor Emeritus Sam Bowring. From each sample, the researchers isolated individual grains of zircon, a common mineral in rocks that contains uranium and some lead, the ratio of which scientists can measure to get an estimate of the rock’s age.
From their analyses, Klein and his colleagues discovered that the age of all nine samples spanned a surprisingly short range, of just 1.39 million years. The team calculated an estimate for the amount of magma that must have crystallized to form the new crust that the samples represent. They found that about 250 cubic kilometers of magma likely rose up from Earth’s interior and transformed into new crust — in just 1.39 million years.
“That’s about two-and-a-half times faster than previous estimates for crust formation in the Sierras, which is a pretty big difference,” Klein says. “It gives us a maximum speed limit for how quickly these things can actually happen.”
Klein says that given the speed of this new crust formation, the likely cause was a magma flareup, or sudden burst of magmatic activity.
“The entire batholith was constructed in almost 200 million years, but we know over that period of time, there were periods when it was highly active and periods that were quieter, with less new material added,” Klein says. “What we were able to show in this area was that, at least locally, the rate at which magma was brought in is much faster than the average rates that have been documented in the Sierras.”
Geologists have thought that magma flare-ups occur as a result of unusual activity in the Earth, such as tectonic plates suddenly colliding at a faster rate. According to everything researchers have documented about the Bear Valley Intrusive Suite, however, no such activity transpired at the time the mountain range formed.
“There’s no obvious trigger,” Klein says. “The system is pretty much going along, and then we see this big burst of magma. So this challenges some basic notions in the field, and should inform how people think of how quickly these things could be happening today, in places like the Andes or the volcanos in Japan.”
This research was supported, in part, by the National Science Foundation. More

It’s an amazing moment when a topic learned in the classroom comes to life. For senior Darya Guettler, that moment came on a sweltering day while installing solar panels in low-income communities in Los Angeles, alongside workers who had been previously incarcerated.
Guettler was volunteering with an MIT Energy Initiative program called Solar Spring Break, which had partnered with Homeboy Industries, an organization that supports formerly incarcerated individuals through career opportunities in green energy. Drilling the panels into the roofs while sweat dripped down her neck, Guettler finally got a chance to see the utility of solar panels in action. When the volunteers switched on the lights, the members of the community got together and celebrated.
“I’ve never done that before, and it was a very unique experience,” Guettler says, recalling the internship. “As students, we’re usually designing the solar panels. Actually installing them and then turning the power on — it’s like all these families now have power for free and can finally run their air conditioning during the day. It made it all feel real.”
Guettler’s fascination with renewable energy began back in high school geography class. Listening to lectures on fuel scarcity, she wondered why renewable energy sources weren’t more widely implemented. Her curiosity encouraged her to research solar panel efficiency and galvanic cell temperature concentrations.
She arrived at MIT with the goal of mitigating climate change through technological innovation, and soon joined the MIT Undergraduate Energy Club, where she says she met inspiring and equally passionate students. Over time, they helped to shape her mindset about what her role could be in helping with the climate crisis. Now the club’s president, Guettler has been working to expand the club’s education outreach programs and encourage kids to get excited about ways they can use engineering to help the planet.
Although Guettler had long understood the need to improve solar technologies, it wasn’t until her Solar Spring Break experience that she made the connection between climate change and the need to involve many different parties in putting together solutions.
“After that, I was kind of hooked on the policy side as well, because I saw that there’s really a space for combining all these things,” she says. “Now all of a sudden it wasn’t just about employing the technology, which I had always been interested in, but also about who was going to be employing it, where it was going to be placed, and how we could make that process as equitable as possible.”
Guettler decided to combine her mechanical engineering major with a degree in political science and has gravitated to classes focused on the intersection of sustainable technologies and climate policy.
“They’re really interesting classes. I’ve got a class about engineering democratic development, one about election modeling, and one in energy storage,” she says. “Honestly, sometimes it’s hard to pick. There’s so many I want to take!”
But of all her classes, one that Guettler is most looking forward to now is her capstone for mechanical engineering, 2.s009 (Explorations in Product Design). The class — which this year challenges students to create social impact projects centered around kindness — begins by placing students into groups and giving them a budget. The groups then design a product and come up with a prototype and a business pitch for it.
“The kindness aspect is pretty much up to the group to decide,” Guettler explains. “It can a project centered around climate change, environmental protection, helping people with disabilities, assisting marginalized communities — I’m super excited to see what people come up with.”
Guttler spent the past summer working in consulting, and in her spare time taught middle and high school students about climate change from her remote cabin in Maine. The classes were taught through MIT Splash, which allows MIT students to teach any topic of their choice to interested younger students.
“It was all online, but it was really fun,” she says. “We just kind of talked about climate models and used this cool tool where you can adjust different policy factors and just see what happens. The kids had so many questions, and I loved getting to build their interest and talk about it with them.”
Talking with people of all ages and backgrounds about ways we can develop a more sustainable future has been a consistent theme throughout Guettler’s experience at MIT. Last year, she visited West Point for the Student Conference on U.S. Affairs, where she spoke with military advisors and generals about the concerns of climate change from a national security perspective.
“I was really interested to see that climate change is also a really big issue to them too, since there’s a lot of bases near coastal waters that will be under threat when sea levels rise,” she says. “There’s definitely been a wide range of people I’ve interacted with about the climate change crisis, but at the end of the day, it’s always the same core concepts. I love hearing people’s different ideas, because more people means more potential solutions, and honestly, at this point, we need any solutions we can get.”
As an elected student to the MIT Committee on Outside Engagements, as well as a founding member of MIT Divest, Guettler hasn’t been shy about the importance of holding political leaders and officials accountable for their decisions.
“I was talking a lot with students to see what they held as important values and what they wanted MIT to represent. Climate action kept on coming up, which led to a bigger discussion of who MIT engages with.”
Her experience so far has been positive overall, and she notes that student representatives have been given a seat on MIT’s Climate Action Advisory Committee, as well as been able to contribute to the MIT Climate Action Plan. The inclusion has allowed students to advocate for ways MIT can take initiative to reduce and offset their energy emissions.
While Guettler recognizes that major institutions have the largest immediate impact on improving the climate crisis, she still wants everyone to recognize the importance of individual actions as well.
“My message to everyone right now is just go and vote, just please go and do that. I’ve been phone banking for different state races right now and people have been hanging up in my face or cursing me out, saying it’s not that serious. I’m like, are you serious?” she laughs. “I honestly think voting right now is the best thing you can do for the climate. Even if you’re feeling overwhelmed, even if you don’t feel like you can make an impact — you have an important decision that you can make. Now just go and vote for it!” More

The Southern Ocean surrounding Antarctica is a region where many of the world’s carbon-rich deep waters can rise back up to the surface. Scientists have thought that the vast swaths of sea ice around Antarctica can act as a lid for upwelling carbon, preventing the gas from breaking through the ocean’s surface and returning to the atmosphere.
However, researchers at MIT have now identified a counteracting effect that suggests Antarctic sea ice may not be as powerful a control on the global carbon cycle as scientists had suspected.
In a study published in the August issue of the journal Global Biogeochemical Cycles, the team has found that indeed, sea ice in the Southern Ocean can act as a physical barrier for upwelling carbon. But it can also act as a shade, blocking sunlight from reaching the surface ocean. Sunlight is essential for phytosynthesis, the process by which phytoplankton and other ocean microbes take up carbon from the atmosphere to grow.
The researchers found that when sea ice blocks sunlight, biological activity — and the amount of carbon that microbes can sequester from the atmosphere — decreases significantly. And surprisingly, this shading effect is almost equal and opposite to that of sea ice’s capping effect. Taken together, both effects essentially cancel each other out. 
“In terms of future climate change, the expected loss of sea ice around Antarctica may therefore not increase the carbon concentration in the atmosphere,” says lead author Mukund Gupta, who carried out the research as a graduate student in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS).
He emphasizes that sea ice does have other effects on the global climate, foremost through its albedo, or ability to reflect solar radiation.
“When the Earth warms up, it loses sea ice and absorbs more of this solar radiation, so in that sense, the loss of sea ice can accelerate climate change,” Gupta says. “What we can say here is, sea ice changes may not have such a strong effect on carbon outgassing around Antarctica through this capping and shading effect.”
Gupta’s coauthors are EAPS Professor Michael “Mick” Follows, and EAPS research scientist Jonathan Lauderdale.
The role of ice
Each winter, wide swaths of the Southern Ocean freeze over, forming vast sheets of sea ice that extend out from Antarctica for millions of square miles. The role of Antarctic sea ice in regulating the climate and the carbon cycle has been much debated, though the prevailing theory has been that sea ice can act as a lid to keep carbon in the ocean from escaping to the atmosphere.
“This theory is mostly thought of in the context of ice ages, when the Earth was much colder and the atmospheric carbon was lower,” Gupta says. “One of the theories explaining this low carbon concentration argues that because it was colder, a thick sea ice cover extended further into the ocean, blocking carbon exchanges with the atmosphere and effectively trapping it in the deep ocean.”
Gupta and his colleagues wondered whether an effect other than capping may also be in play. In general, the researchers have sought to understand how various features and processes in the ocean interact with ocean biology such as phytoplankton. They assumed that there might be less biological activity as a result of sea ice blocking microbes’ vital sunlight — but how strong would this shading effect be?
Equal and opposite
To answer that question, the researchers used the MITgcm, a global circulation model that simulates the many physical, chemical, and biological processes involved in the circulation of the atmosphere and ocean. With MITgcm, they simulated a vertical slice of the ocean spanning 3,000 kilometers wide and about 4,000 meters deep, and with conditions similar to today’s Southern Ocean. They then ran the model multiple times, each time with a different concentration of sea ice.
“At 100 percent concentration, there are no leaks in the ice, and it’s really compacted together, versus very low concentrations representing loose and sparse ice floes moving around,” Gupta explains.
They set each simulation to one of three scenarios: one where only the capping effect is active, and sea ice is only influencing the carbon cycle by preventing carbon from leaking back out to the atmosphere; another where only the shading effect is active, and sea ice is only blocking sunlight from penetrating the ocean; and the last in which both capping and shading effects are in play.
For every simulation, the researchers observed how the conditions they set affected the overall carbon flux, or amount of carbon that escaped from the ocean to the atmosphere.
They found that capping and shading had opposite effects on the carbon cycle, reducing the amount of carbon to the atmosphere in the former case and increasing it in the latter, by equal amounts. In the scenarios where both effects were considered, one canceled the other out almost entirely, across a wide range of sea ice concentrations, leading to no significant change in the carbon flux. Only when sea ice was at its highest concentration did capping have the edge, with a decrease in carbon escaping to the atmosphere.
The results suggest that Antarctic sea ice may effectively trap carbon in the ocean, but only when that ice cover is very expansive and thick. Otherwise, it seems that sea ice’s shading effect on the underlying organisms may counteract its capping effect.
“If one just considered the physics and the pure capping, or carbon barrier idea, that would be an incomplete way of thinking about it,” Gupta says. “This shows that we need to understand more of the biology under sea ice and how it underlies this effect.”
This research was supported in part by the U.S. National Science Foundation. More

Researchers at MIT have modeled how engineered and natural wood jams change river water levels, enabling an assessment of the trade-offs in flood risk and habitat creation for river restoration projects.
In a recent paper published in Geophysical Research Letters, researchers Elizabeth Follett ’09 PhD ’16, postdoc Isabella Schalko, and Donald and Martha Harleman Professor of Civil and Environmental Engineering Heidi Nepf detail their analysis of 584 experiments measuring the backwater rise induced by model logjams in an experimental flume. Schalko ran these experiments, with the hope of filling gaps of the previously understudied physical processes to better explain just how water flow is impacted by large, densely packed groups of logs and to better inform current and future flood risk as well as river restoration projects.
“We’ve been missing a way to describe the physical mechanisms by which large groups of wood pieces affect the river water level,” says Follett, who is the lead author on the paper and a Royal Academy of Engineering Research Fellow at Cardiff University. “Our work allows researchers to characterize structural properties of wood jams from field measurements, by measuring the river water level up- and downstream of the jam and applying our new model.”
The team hopes that the structural metrics will be useful for a wide range of scientists and engineers. The paper has also had an unintended benefit: bridging gaps between research groups.
“What I like most about the paper is that it brings together two research communities; those who look more at in-stream wood, and those more interested in canopy shear flows,” says Schalko.
The findings could have significant implications for government or non-profit organizations engaging in restoration projects. According to the researchers, there is growing interest all over the world in river restoration projects; up until now, it was understood that adding wood to rivers was good for restoration because wood increases flow heterogeneity by increasing water depth. Despite the growing popularity of wood as a solution, the physical processes have not been studied in depth and are not always accounted for in flood prediction models.
“Flood risk and river restoration projects have attracted recent investments, but up to now it has been difficult to include the effect of wood in flood models to improve the design and assessment of these projects,” says Follett. “This is a first step in the direction of being able to theoretically describe how wood alters the flow conditions in a river.” When joined with existing information, the new data on wood jams should better inform flood risk and river restoration efforts in the future. More

MIT graduate student Annauk Denise Olin didn’t grow up speaking Iñupiaq, the language of her Alaska Native community. Nevertheless, she’s raising her son in the language — thanks in part to the grounding in linguistics she is gaining through the MIT Indigenous Language Initiative (MITILI), a master’s program for members of communities whose languages are threatened.“The beauty of the Iñupiaq language is that the perspective and the wisdom of my ancestors has been preserved in the language,” says Olin, who is developing a curriculum for teaching Iñupiaq through MITILI. “If we lose our language, we lose our ability to see into the minds of the people who were able to thrive — for millennia — in one of the harshest climates in the world.”That climate has been rapidly changing in the last two decades, with disastrous consequences for Olin’s family’s village, Shishmaref. A small community of about 600 people, Shishmaref is perched on tiny Sarichef Island just south of the Arctic Circle — a place where reduced sea ice, melting permafrost, and other impacts of climate change have come to threaten the community’s very existence. The effect of global climate change on Shishmaref is seen as among “the most dramatic in the world.”“We’ve had several homes fall into the ocean. We’ve lost hundreds and hundreds of feet of land on our island. Historically, we would expect sea ice to form around our island in September or October. In the last few years, we had winters where sea ice would not form until January. This should serve as a warning to the rest of the world,” says Annauk, noting that the village has sought federal help to move to a new location — so far in vain.
Navigating climate change in ShishmarefHelping her community to navigate the huge challenges presented by climate change is a key motivator for Olin, who started learning the Iñupiaq language intensively in 2016. At the time, she was working full time at the Alaska Institute for Justice (AIJ), a nonprofit dedicated to protecting the human rights of all Alaskans. As the research director of the AIJ’s climate change research and policy center, she worked with 15 Alaska Native villages (including Shishmaref) to begin developing a community-led relocation governance framework.She says that language issues can present a barrier to such projects because elders in Alaska Native communities are not always fluent and literate in English, and the government rarely communicates in Iñupiaq. In fact, just this past January, Olin and members of the native village of Shishmaref partnered with the Alaska Public Research Interest Group to help produce census materials in Iñupiaq to fill this gap.“Alaska has been historically underrepresented in the census,” she says. “We created public service announcements with speakers of Alaska Native languages to get more Alaska Native people to participate in the census so we can get adequate funding for our communities.” A language shaped by the ArcticOlin began teaching Iñupiaq after just one year of study at the Alaska Native Heritage Center in Anchorage. “Teaching and learning a language at the same time is very challenging and time-consuming, but it’s common for second-language learners of endangered languages,” she says. One thing she’s learned so far is that Iñupiaq has almost 100 different terms for ice, but not for all of the conditions that people see today in Alaska; essentially, words fail to convey the devastation that climate change has wrought on the Arctic landscape.

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MIT graduate student Annauk Denise Olin describes in the Iñupiaq language the family members who share a meal at her grandmother’s house in Shishmaref, Alaska.

“The Iñupiaq language has a complex and robust lexicon related to ice conditions in part because it is linked to our survival. If you’re out hunting and you aren’t able to describe to your hunting partner whether the ice is stable enough, it could cost your lives,” she says. “With climate change, some elders don’t have in their vocabulary words to describe how the ice is changing, so I think what’s important in the future is for us to be able to adapt the language to be able to describe these changing conditions exactly.”For Olin, that means there need to be more young Iñupiaq speakers. “We need resources to teach in the language so that we have an upcoming generation of speakers even after our beloved elders pass on,” she said, noting that she is hoping her efforts will help undo the damage done by missionaries and the U.S. government, which for more than 100 years forced Iñupiat children to speak English in school.
A foundation in linguisticsOlin is beginning this work at home by speaking Iñupiaq to her son. “When I speak English to my son, it feels like a watered-down version of love, but when I speak Iñupiaq to him, the connection I feel with him is much stronger and intimate.”To ensure that she is using the language properly, she is working with a mentor, native speaker Edna Ahgeak MacLean, a former faculty member at the University of Alaska Fairbanks and former president of Iḷisaġvik College. MacLean, who has produced both an Iñupiaq dictionary and a grammar, has helped Olin to script conversations so that she and her husband (a tribal member from another Alaska Native group, the Koyukon Athabascan, who speak Denaa’kke) can engage in simple activities — such as making pancakes — while conversing entirely in Iñupiaq.At the same time, Olin is developing a curriculum for teaching Iñupiaq through her work at MITILI. Inspired by the work of the late MIT Professor Ken Hale, who dedicated his career to the study and support of indigenous languages of the Americas and of Australia, MITILI is a two-year program that provides a full scholarship that covers tuition, fees and health insurance, plus a stipend.Olin is taking linguistics classes and working with her MIT advisor, Professor Norvin Richards, to gain an understanding of phonology, syntax, and language acquisition. “Some of the critical materials my mentor has written use many linguistic terms and concepts,” she says. “It has made a huge difference to be able to understand what tools are available to break down a lot of these linguistics-heavy resources.”For example, Richards has helped Olin better understand how to combine morphemes, the smallest units of meaning in a language, to create words. “There are complicated rules that must be followed and practiced to correctly string morphemes together in Iñupiaq,” she says. For instance, in Iñupiaq it’s common for a morpheme to be attached to a word stem to indicate an action or state of being, a function usually performed in English by a verb. Long-term survival of indigenous languages“One of the things I appreciate about Annauk’s work on Iñupiaq is how intellectually omnivorous she is,” says Richards, who has for decades worked to help revive endangered languages, including Wampanoag, a native language of Eastern Massachusetts, and Lardil, an Aboriginal language of Australia. “She’s able to build on very careful work by the great Iñupiaq scholar Edna Ahgeak MacLean, but she’s clearly determined to develop a language program that incorporates every technique that she thinks will work.”Noting that the indigenous languages of the United States are all threatened, Richards says Olin is doing work that is critical to maintaining the world’s linguistic diversity — learning Iñupiaq “through sheer force of will.” “She’s tireless and dedicated, and very smart,” he says. “It’s a real privilege to get to work with her.”Supporting students like Olin has been the central mission of the MITILI since its founding in 2004. “The goals of the MITILI are ones that Ken Hale spoke and wrote about, eloquently and often,” Richards says. “One is to improve our understanding of the languages of the world, not by subjecting indigenous languages to study by outsiders, but by offering indigenous scholars ways to study their own languages with the tools that academic linguists have developed. And another, at least as important, is to try to help indigenous communities give their traditional languages their best chance of long-term survival.”Olin’s ultimate goal is to fulfill this mission for her community, and her initial plan is to create an Iñupiaq mentor-apprenticeship program. “I’m also very interested in creating a school where the mission, leadership, and content is driven by Iñupiaq people and community — where we learn the language but also how to harvest and process traditional foods, sew traditional clothing, and most importantly, how to treat one another as human beings,” she says.“As an Iñupiat, it is my responsibility to help provide a place where young people can have access to their identity and culture,” Olin says. “Many of our Iñupiat people are working to overcome historical trauma. Language is a powerful medicine that will help heal our communities.”
Story prepared by MIT SHASS CommunicationsEditorial and design director: Emily HiestandSenior writer: Kathryn O’Neil More

An interdepartmental team of environmental scientists from MIT has received funding to develop a new program, called the MIT Integrative Microbiology Initiative (MIMI), aimed at enhancing the study of environmental sciences at MIT. The team of researchers and faculty, led by Professor Otto X. Cordero of the Department of Civil and Environmental Engineering, hopes the new initiative will build on the rich history of Parsons Laboratory as a leader of the environmental science space, and help identify and develop the next generation of leaders in the field.
“The main goal of this initiative for me was to expand and reinvigorate environmental microbiology at MIT”, says Cordero. “There is a certain sense that treating and diagnosing human disease is the primary end goal of life sciences. That should not be the case. Microbes control the elemental cycles of the planet and are key for agriculture, bioenergy, biodegradation of novel materials, etc. Thus, finding solutions to some of the most pressing problems for humanity hinges on being able to understand and engineer environmental microbiomes”.
The $2.1 million funding for the program, provided by The Simons Foundation, will support first-year graduate students who join the interdepartmental microbiology PhD program at MIT, and who are interested in environmental problems. The group hopes to leverage the strong program to help build the new initiative.
“The program offers a very select group of people — every year there are around 200 applicants and six are accepted — they can go work in physics, in CEE, in biology, in chemistry, etc. — it’s a really fantastic program,” says Cordero. With program funding and support, the group hopes to increase the number of accepted applicants each year and, over time, build a robust community.
Funding for the program will also support the “social infrastructure” of the program — seminars that bring together microbiologists from different departments. Eventually, as part of the initiative as well, the group plans to incorporate retreats designed to increase interaction and collaboration among environmental scientists across the Institute.
Collaborators on the project include Institute Professor Sallie “Penny” Chisholm and Assistant Professor Tami Leiberman, both CEE affiliates; as well as several members of the Department of Earth, Atmospheric and Planetary Sciences: Professor Tonja Bosak, Professor Michael Follows, Assistant Professor Gregory Fournier, and Assistant Professor Andrew Babbin.
The hope for Cordero and his group is that the new interdepartmental initiative will build bridges between environmental sciences in all sectors at MIT, create a strong community of researchers, and inspire collaboration. More

Some of the oldest remains of early human ancestors have been unearthed in Olduvai Gorge, a rift valley setting in northern Tanzania where anthropologists have discovered fossils of hominids that existed 1.8 million years ago. The region has preserved many fossils and stone tools, indicating that early humans settled and hunted there.
Now a team led by researchers at MIT and the University of Alcalá in Spain has discovered evidence that hot springs may have existed in Olduvai Gorge around that time, near early human archaeological sites. The proximity of these hydrothermal features raises the possibility that early humans could have used hot springs as a cooking resource, for instance to boil fresh kills, long before humans are thought to have used fire as a controlled source for cooking.
“As far as we can tell, this is the first time researchers have put forth concrete evidence for the possibility that people were using hydrothermal environments as a resource, where animals would’ve been gathering, and where the potential to cook was available,” says Roger Summons, the Schlumberger Professor of Geobiology in MIT’s Department of Earth, Atmospheric, and Planetary Sciences (EAPS).  
Summons and his colleagues have published their findings today in the Proceedings of the National Academy of Sciences. The study’s lead author is Ainara Sistiaga, a Marie Skłodowska-Curie fellow based at MIT and the University of Copenhagen. The team includes Fatima Husain, a graduate student in EAPS, along with archaeologists, geologists, and geochemists from the University of Alcalá and the University of Valladolid, in Spain; the University of Dar es Salaam, in Tanzania; and Pennsylvania State University.
An unexpected reconstruction
In 2016, Sistiaga joined an archaeological expedition  to Olduvai Gorge, where researchers with the Olduvai Paleoanthropology and Paleoecology Project were collecting sediments from a 3-kilometer-long layer of exposed rock that was deposited around 1.7 million years ago. This geologic layer was striking because its sandy composition was markedly different from the dark clay layer just below, which was deposited 1.8 million years ago.
“Something was changing in the environment, so we wanted to understand what happened and how that impacted humans,” says Sistiaga, who had originally planned to analyze the sediments to see how the landscape changed in response to climate and how these changes may have affected the way early humans lived in the region.
It’s thought that around 1.7 million years ago, East Africa underwent a gradual aridification, moving from a wetter, tree-populated climate to dryer, grassier terrain. Sistiaga brought back sandy rocks collected from the Olduvai Gorge layer and began to analyze them in Summons’ lab for signs of certain lipids that can contain residue of leaf waxes, offering clues to the kind of vegetation present at the time.
“You can reconstruct something about the plants that were there by the carbon numbers and the isotopes, and that’s what our lab specializes in, and why Ainara was doing it in our lab,” Summons says. “But then she discovered other classes of compounds that were totally unexpected.”
An unambiguous sign
Within the sediments she brought back, Sistiaga came across lipids that looked completely different from the plant-derived lipids she knew. She took the data to Summons, who realized that they were a close match with lipids produced not by plants, but by specific groups of bacteria that he and his colleagues had reported on, in a completely different context, nearly 20 years ago.
The lipids that Sistiaga extracted from sediments deposited 1.7 million years ago in Tanzania were the same lipids that are produced by a modern bacteria that Summons and his colleagues previously studied in the United States, in the hot springs of Yellowstone National Park.
One specific bacterium, Thermocrinis ruber, is a hyperthermophilic organism that will only thrive in very hot waters, such as those found in the outflow channels of boiling hot springs.
“They won’t even grow unless the temperature is above 80 degrees Celsius [176 degrees Fahrenheit],” Summons says. “Some of the samples Ainara brought back from this sandy layer in Olduvai Gorge had these same assemblages of bacterial lipids that we think are unambiguously indicative of high-temperature water.”
That is, it appears that heat-loving bacteria similar to those Summons had worked on more than 20 years ago in Yellowstone may also have lived in Olduvai Gorge 1.7 million years ago. By extension, the team proposes, high-temperature features such as hot springs and hydrothermal waters could also have been present.
“It’s not a crazy idea that, with all this tectonic activity in the middle of the rift system, there could have been extrusion of hydrothermal fluids,” notes Sistiaga, who says that Olduvai Gorge is a geologically active tectonic region that has upheaved volcanoes over millions of years — activity that could also have boiled up groundwater to form hot springs at the surface.
The region where the team collected the sediments is adjacent to sites of early human habitation featuring stone tools, along with animal bones. It is possible, then, that nearby hot springs may have enabled hominins to cook food such as meat and certain tough tubers and roots.
“The authors’ comprehensive analyses paint a vivid picture of the ancient Olduvai Gorge ecosystem and landscape, including the first compelling evidence for ancient hydrothermal springs,” says Richard Pancost, a professor of biogeochemistry at the University of Bristol, who was not involved in the study. “This introduces the fascinating possibility that such springs could have been used by early hominins to cook food.”
“Why wouldn’t you eat it?”
Exactly how early humans may have cooked with hot springs is still an open question. They could have butchered animals and dipped the meat in hot springs to make them more palatable. In a similar way, they could have boiled roots and tubers, much like cooking raw potatoes, to make them more easily digestible. Animals could have also met their demise while falling into the hydrothermal waters, where early humans could have fished them out as a precooked meal.
“If there was a wildebeest that fell into the water and was cooked, why wouldn’t you eat it?” Sistiaga poses.
While there is currently no sure-fire way to establish whether early humans indeed used hot springs to cook, the team plans to look for similar lipids, and signs of hydrothermal reservoirs, in other layers and locations throughout Olduvai Gorge, as well as near other sites in the world where human settlements have been found.
“We can prove in other sites that maybe hot springs were present, but we would still lack evidence of how humans interacted with them. That’s a question of behavior, and understanding the behavior of extinct species almost 2 million years ago is very difficult, Sistiaga says. “I hope we can find other evidence that supports at least the presence of this resource in other important sites for human evolution.”
This research was supported, in part, by the European Commission (MSCA-GF), the NASA Astrobiology Institute, and the Government of Spain. More