Environment

On March 1, MIT Solve launched its 2021 Global Challenges, with over $1.5 million in prize funding available to innovators worldwide.
Solve seeks tech-based solutions from social entrepreneurs around the world that address five challenges. Anyone, anywhere can apply to address the challenges by the June 16 deadline. Solve also announced Eric s. Yuan, founder and CEO of Zoom, and Karlie Kloss, founder of Kode With Klossy, as 2021 Challenge Ambassadors. 
To help with the challenge application process, Solve runs a course with MITx entitled “Business and Impact Planning for Social Enterprises,” which introduces core business model and theory-of-change concepts to early stage entrepreneurs. 
Finalists will be invited to attend Solve Challenge Finals on Sept. 19 in New York during U.N. General Assembly week. At the event, they will pitch their solutions to Solve’s Challenge Leadership Groups, judging panels comprised of industry leaders and MIT faculty. The judges will select the most promising solutions as Solver teams.
“After a year of turmoil, including a major threat to our collective health, disruption in schooling, lack of access to digital connectivity and meaningful work, a reckoning in the U.S. after centuries of institutionalized racism, or worsening natural hazards — supporting diverse innovators who are solving these challenges is more urgent than ever,” says Alex Amouyel, executive director of MIT Solve. “Solve is committed to bolstering communities in the U.S. and across the world by supporting innovators who are addressing our 2021 Global Challenges — wherever they are — through funding, mentorship, and an MIT-backed community. Whether you’re a prospective Solve partner or applicant, we hope you’ll join us!” 
Solver teams participate in a nine-month program that connects them to the resources they need to scale. Thanks to its partners, to date Solve has provided over $40 million in commitments for Solver teams and entrepreneurs.
Solve’s challenge design process collects insights and ideas from industry leaders, MIT faculty, and local community voices alike. 
Solve’s 2021 Global Challenges are:
Funders include the Patrick J. McGovern Foundation, General Motors, Comcast NBCUniversal, Vodafone Americas Foundation, HP, Ewing Marion Kauffman Foundation, American Student Assistance, The Robert Wood Johnson Foundation, Andan Foundation, Good Energies Foundation and the Elevate Prize Foundation. The Solve community will convene at Virtual Solve at MIT on May 3-4 with 2020 Solver teams, Solve members, and partners to build partnerships and tackle global challenges in real-time. 
As a marketplace for social impact innovation, Solve’s mission is to solve world challenges. Solve finds promising tech-based social entrepreneurs around the world, then brings together MIT’s innovation ecosystem and a community of members to fund and support these entrepreneurs to help scale their impact. Organizations interested in joining the Solve community can learn more and apply for membership here. More

According to United Nations estimates, the global population is expected to grow by 2 billion within the next 30 years, giving rise to an expected increase in demand for food and agricultural products. Today, biotic and abiotic environmental stresses such as plant pathogens, sudden fluctuations in temperature, drought, soil salinity, and toxic metal pollution — made worse by climate change — impair crop productivity and lead to significant losses in agriculture yield worldwide.
New work from the Singapore-MIT Alliance for Research and Technology (SMART), MIT’s research enterprise in Singapore, and Temasek Life Sciences Laboratory (TLL) highlights the potential of recently developed analytical tools that can provide tissue-cell or organelle-specific information on living plants in real-time and can be used on any plant species.
In a perspective paper titled “Species-independent analytical tools for next-generation agriculture” published in the journal Nature Plants, researchers from the Disruptive and Sustainable Technologies for Agricultural Precision (DiSTAP) Interdisciplinary Research Group (IRG) within SMART review the development of two next-generation tools, engineered plant nanosensors and portable Raman spectroscopy, to detect biotic and abiotic stress, monitor plant hormonal signalling, and characterize soil, phytobiome, and crop health in a non- or minimally invasive manner. The researchers discuss how the tools bridge the gap between model plants in the laboratory and field application for agriculturally relevant plants. The paper also assesses the future outlook, economic potential, and implementation strategies for the integration of these technologies in future farming practices.
An estimated 11-30 percent yield loss of five major crops of global importance (wheat, rice, maize, potato, and soybean) is caused by crop pathogens and insects, with the highest crop losses observed in regions already suffering from food insecurity. Against this backdrop, research into innovative technologies and tools is required for sustainable agricultural practices to meet the rising demand for food and food security — an issue that has drawn the attention of governments worldwide due to the Covid-19 pandemic.
Plant nanosensors, developed at SMART DiSTAP, are nanoscale sensors — smaller than the width of a hair — that can be inserted into the tissues and cells of plants to understand complex signalling pathways. Portable Raman spectroscopy, also developed at SMART DiSTAP, encompases a laser-based device that measures molecular vibrations induced by laser excitation, providing highly specific Raman spectral signatures that provide a fingerprint of a plant’s health. These tools are able to monitor stress signals in short time-scales, ranging from seconds to minutes, which allows for early detection of stress signals in real-time.
“The use of plant nanosensors and Raman spectroscopy has the potential to advance our understanding of crop health, behavior, and dynamics in agricultural settings,” says Tedrick Thomas Salim Lew SM ’18, PhD ’20, the paper’s first author. “Plants are highly complex machines within a dynamic ecosystem, and a fundamental study of its internal workings and diverse microbial communities of its ecosystem is important to uncover meaningful information that will be helpful to farmers and enable sustainable farming practices. These next-generation tools can help answer a key challenge in plant biology, which is to bridge the knowledge gap between our understanding of model laboratory-grown plants and agriculturally-relevant crops cultivated in fields or production facilities.”
Early plant stress detection is key to timely intervention and increasing the effectiveness of management decisions for specific types of stress conditions in plants. Tools capable of studying plant health and reporting stress events in real-time will benefit both plant biologists and farmers. Data obtained from these tools can be translated into useful information for farmers to make management decisions in real-time to prevent yield loss and reduced crop quality.
The species-independent tools also offer new plant science study opportunities for researchers. In contrast to conventional genetic engineering techniques that are only applicable to model plants in laboratory settings, the new tools apply to any plant species, which enables the study of agriculturally relevant crops previously understudied. Adopting these tools can enhance researchers’ basic understanding of plant science and potentially bridge the gap between model and non-model plants.
“The SMART DiSTAP interdisciplinary team facilitated the work for this paper and we have both experts in engineering new agriculture technologies and potential end-users of these technologies involved in the evaluation process,” says Professor Michael Strano, the paper’s co-corresponding author, DiSTAP co-lead principal investigator, and the Carbon P. Dubbs Professor of Chemical Engineering at MIT. “It has been the dream of an urban farmer to continually, at all times, engineer optimal growth conditions for plants with precise inputs and tightly controlled variables. These tools open the possibility of real-time feedback control schemes that will accelerate and improve plant growth, yield, nutrition, and culinary properties by providing optimal growth conditions for plants in the future of urban farming.”
“To facilitate widespread adoption of these technologies in agriculture, we have to validate their economic potential and reliability, ensuring that they remain cost-efficient and more effective than existing approaches,” the paper’s co-corresponding author, DiSTAP co-lead principal investigator, and deputy chair of TLL Professor Chua Nam Hai explains. “Plant nanosensors and Raman spectroscopy would allow farmers to adjust fertilizer and water usage, based on internal responses within the plant, to optimize growth, driving cost efficiencies in resource utilization. Optimal harvesting conditions may also translate into higher revenue from increased product quality that customers are willing to pay a premium for.”
Collaboration among engineers, plant biologists, and data scientists, and further testing of new tools under field conditions with critical evaluations of their technical robustness and economic potential will be important in ensuring sustainable implementation of technologies in tomorrow’s agriculture.
DiSTAP Scientific Advisory Board members Professor Kazuki Saito, group director of Metabolomics Research Group at RIKEN Center for Sustainable Resource Science, and Hebrew University of Jerusalem Professor Oded Shoseyov also co-authored the paper.
The research is carried out by SMART and supported by the National Research Foundation (NRF) Singapore under its Campus for Research Excellence And Technological Enterprise (CREATE) program.
DiSTAP is one of the five IRGs of SMART. The DiSTAP program addresses deep problems in food production in Singapore and the world by developing a suite of impactful and novel analytical, genetic, and biosynthetic technologies. The goal is to fundamentally change how plant biosynthetic pathways are discovered, monitored, engineered, and ultimately translated to meet the global demand for food and nutrients. Scientists from MIT, TLL, Nanyang Technological University, and National University of Singapore are collaboratively developing new tools for the continuous measurement of important plant metabolites and hormones for novel discovery, deeper understanding and control of plant biosynthetic pathways in ways not yet possible, especially in the context of green leafy vegetables; leveraging these new techniques to engineer plants with highly desirable properties for global food security, including high-yield density production, drought and pathogen resistance, and biosynthesis of high-value commercial products; developing tools for producing hydrophobic food components in industry-relevant microbes; developing novel microbial and enzymatic technologies to produce volatile organic compounds that can protect and/or promote growth of leafy vegetables; and applying these technologies to improve urban farming. More

In an ongoing series, Solving Climate: Humanistic Perspectives from MIT, faculty, students, and alumni in the Institute’s humanistic fields share scholarship and insights that are significant for solving climate change and mitigating its myriad social and ecological impacts.Clare Balboni is the 3M Career Development Assistant Professor of Environmental Economics at MIT and an affiliate of MIT’s Center for Energy and Environmental Policy Research. Her research centers on environmental economics, trade, and development economics. In this Q&A with MIT SHASS Communications, she describes the burgeoning influence of economics in understanding climate, energy, and environmental issues, as well as informing related policy.Q: In what ways are the research, insights, and perspectives from economics significant for addressing global change and its myriad ecological and social impacts?A: There is tremendous and growing interest in environmental questions within economics. Economic models and methods can help to enhance our understanding of how to balance the imperative for continued growth in prosperity and well-being — particularly for the world’s poorest — with the need to mitigate and adapt to the environmental externalities that this growth creates.Environmental economists have taken advantage of economic tools and methodologies, and the rapid proliferation of new data sources, to study how local pollutants and greenhouse gas emissions affect a huge range of outcomes spanning such areas as mortality, health, agriculture, labor productivity, income, migration, education, crime, and conflict. Building a strong evidence base on the consequences of environmental quality, and developing techniques for measuring environmental benefits and harms, is key in informing the design of emissions reduction policies.Another important contribution of economics is to provide robust analysis of policies that aim to tackle environmental externalities through, for instance, taxation, tradable emissions permits, regulation, and innovation policy. Recent work provides rigorous empirical evidence evaluating key environmental policies and considering important aspects of the design of economic instruments; this work builds on a longstanding body of literature within economics studying environmental policy instruments.A growing body of empirical work in environmental economics focuses on particular issues relating to environmental quality and instrument design in developing countries, where energy use is increasing rapidly; political economy considerations may raise distinct challenges; and where both local pollutant concentrations and projected climate damages are often particularly acute.Q: When you confront an issue as formidable as climate change, what gives you hope?A: I draw hope from the rapidly increasing focus and attention on environmental questions across fields in economics, across disciplines in the social and natural sciences, and more broadly in the academic, policy, and popular discourse. Given the scale and breadth of the challenge, it is crucial that this combined focus from a range of perspectives continues to advance this important agenda.
Series prepared by MIT SHASS CommunicationsSeries editor and designer: Emily HiestandCo-editor: Kathryn O’Neill More

A potent ozone-depleting chemical whose emissions unexpectedly spiked in recent years has quickly dropped back to much lower levels, putting the recovery of the stratospheric ozone layer back on track, according to a new study by scientists at MIT, the University of Bristol, and other institutions in South Korea, the U.S., Japan, Australia, and Switzerland.
The chemical in question is CFC-11, a chlorofluorocarbon that was once commonly used for refrigeration, insulation, and other purposes. When emitted to the atmosphere, CFC-11 can loft into the stratosphere, where the sun’s ultraviolet radiation breaks the chemical down to release chlorine — a noxious chemical that then eats away at ozone, stripping away the Earth’s natural shield against UV rays.
CFC-11 and other chlorofluorocarbons are now banned under the Montreal Protocol, an international treaty under which every country agreed to phase out the chemicals’ production and use by 2010. But in 2018, a team of scientists reported a concerning spike in global emissions of the chemical beginning in 2013.  In 2019, a second team reported that a significant portion of the emissions could be traced to eastern China, predominately the Shandong and Hebie provinces.
Now, in two papers published today in Nature, the same teams report that global annual emissions of CFC-11 into the atmosphere have declined sharply, by about 20,000 U.S. tons, from 2018 to 2019. The researchers traced a substantial fraction of the global emission reductions to the very same regions of eastern China where they had previously reported the original spike. The results are consistent with evidence that the country has taken successful actions to stamp out illegal production of this ozone-depleting chemical.
“This is tremendously encouraging,” says Ronald Prinn, the director of the Center for Global Change Science at MIT and a co-author on both papers. “If emissions of CFC-11 had continued to rise or even just leveled off, there would have been a much bigger problem building up. The global monitoring networks really caught this spike in time, and subsequent actions have lowered emissions before they became a real threat to recovery of the ozone layer.”
A brief history of the spike
Both the original spike and subsequent drop in CFC-11 emissions were detected by the researchers using two independent networks.
One is a global monitoring network operated by the National Oceanographic and Atmospheric Administration (NOAA), comprising about 30 stations. Researchers at each site collect air samples and send them to a central laboratory, where the air is analyzed for CFC-11 and many other trace gases. The weekly measurements, from sites around the world, give an accurate average picture of the chemical species circulating in the global atmosphere.
The other network is the Advanced Global Atmospheric Gases Experiment, or AGAGE, an MIT-led effort funded in part by NASA, with more than a dozen monitoring stations situated on coastal and mountain sites around the world. The AGAGE stations take automated on-site measurements of passing air parcels about every hour, monitoring for more than 50 trace gases, including CFC-11, to provide detailed records of the regional and global atmosphere.
In a 2018 Nature report, the researchers analyzed measurements from NOAA and observed that, from 2014 to 2016, global emissions of CFC-11 grew by more than 14,000 U.S. tons a year — a 25 percent increase from emissions between 2002 and 2012. In a subsequent 2019 Nature report, regional measurements taken by AGAGE stations in Hateruma, Japan, and Gosan, South Korea, along with three-dimensional modeling, showed that about half or more of these emissions came from eastern China, primarily from the factory-heavy Shandong and Hebei provinces.
Following these 2018 and 2019 reports, the scientists continued to track the chemical through the atmosphere, at both global and regional levels.
In the first of the two new Nature papers, they analyze both NOAA and AGAGE global data and report a dramatic turnaround: From 2018 to 2019, CFC-11 annual emissions dropped throughout the global atmosphere by about U.S. 20,000 tons, returning to levels prior to 2012, following the chemical’s 2010 global phaseout.
In the second paper, based on AGAGE measurements, the scientists observed that CFC-11 emissions specifically from eastern China hit a peak around 2017. At some point soon afterward, levels began to drop, although the researchers cannot say exactly when the regional turnaround occurred, as the South Korean station sustained typhoon-related damage that resulted in some data gaps. Despite these gaps, the group observed a decline in CFC-11 annual emissions, by about 11,000 U.S. tons from eastern China, through 2019.  
As the researchers write in the paper, “it seems that any substantial delay in ozone-layer recovery has been avoided, perhaps owing to timely reporting, and subsequent action by industry and government in China.”
“Continuous vigilance”
However, there is still work to be done. While it appears that CFC-11 emissions from eastern China have declined, indicating that significant illegal production of the chemical there has ceased, these emissions only account for roughly half of the global emissions. Where the remainder could have come from is still unknown.
In general, CFC-11 is currently emitted in large amounts through leakages during new production and during subsequent use in refrigeration and manufacture of foams. The chemicals can also leak out from “banks” of old, discarded refrigerators and foams, though at a much slower and more diffuse rate than the rapid regional increase observed in 2013.
“The challenge now is to ask, where’s the rest of it coming from?” says Prinn, the  TEPCO Professor of Atmospheric Science in MIT’s Department of Earth, Atmospheric and Planetary Sciences. “We will need to expand measurements and modeling to identify new sources, and continue to keep watch. Hopefully, emission levels will continue to drop.”
Going forward, the scientists hope to add more stations to the AGAGE network, so that they might identify and quantify other regional sources of CFC-11, particularly in rapidly industrializing parts of the world.
“Clearly this story shows that, in order to ensure that countries are adhering to international agreements like the Montreal Protocol, continuous vigilance is required,” Prinn says. “You can’t stop measuring these chemical species and assume the problem is solved.”
This research was supported, in part, by NASA and NOAA. More

George P. Shultz PhD ’49, former U.S. secretary of labor, state, and of the treasury, died peacefully at his home on Feb. 6, at the age of 100. A champion of bipartisanship who for decades urged action on climate change, he leaves a rich legacy forged during more than 70 years of leadership in government, academia, and business.
“A beloved teacher, a brilliant scholar, a visionary leader, a public servant of the highest integrity, and a relentless champion for the breakthrough energy technologies on which the future of our society depends, George Shultz represented the very best of MIT and of our nation,” says MIT President L. Rafael Reif. “We will remember Secretary Shultz for the boundless energy, piercing clarity, and innovative ideas he brought to every role and every conversation. And we are profoundly grateful for the eloquence of his example: a life lived in service to the common good.”
Born in New York City on Dec. 13, 1920, Shultz grew up in Englewood, New Jersey. He graduated from Princeton University in 1942. He was admitted to MIT for a master’s degree program and planned to enroll in 1943, but paused his academic pursuits to enlist in the U.S. Marine Corps during World War II. He served from 1942 to 1945, rising to the rank of captain.
Following his military service, Shultz began what would become more than a decade of scholarship and teaching at MIT. After earning his PhD in industrial economics, he taught economics at the Institute in the Department of Economics and at the Sloan School of Management, first as an assistant professor, then as an associate professor.
“George and I were assistant professors together. That was seventy years ago,” says Robert M. Solow, a professor emeritus of economics. “We remained friends ever after. Even once he got used to being in high office, there was always a bit of that young researcher in him. I can remember his going door-to-door in Nashua, New Hampshire, learning about the lives of the unemployed. Everyone will miss him.”
In 1955, he took a leave of absence from MIT to serve as a senior staff economist on President Dwight D. Eisenhower’s Council of Economic Advisers. From 1957 to 1968, he served at University of Chicago Graduate School of Business as a professor of industrial relations and then as the school’s dean.
He was appointed U.S. secretary of labor under President Richard Nixon in 1969; in this role, he prioritized reduction of poverty and equal employment opportunities, among other initiatives. In 1970, he became the first director of the Office of Management and Budget, a Cabinet-level office, where he worked to advance school desegregation efforts. He then served as U.S. secretary of the treasury, where he co-founded the international organization that later became known as the Group of Seven (G7) nations, formed to pursue shared economic objectives. Shultz served as chairman of the President’s Economic Policy Advisory Board from 1981 to 1982. In the private sector, he held executive roles at Bechtel Group, Inc, from 1974 to 1982.
He is perhaps best known for his tenure as U.S. secretary of state under President Ronald Reagan, from 1982 to 1989. Shultz was a key figure in facilitating de-escalation of tensions between the U.S. and the Soviet Union, helping to draft agreements that led to the end of the Cold War. In 1989, he received the Presidential Medal of Freedom, the nation’s highest civilian honor. From 1989 until his death, he was a distinguished fellow at Stanford University’s Hoover Institution.
Shultz’s affiliation with MIT remained strong over the years. When accepting the Robert A. Muh Award for noteworthy achievement in the humanities, arts, and social sciences at MIT in 2003, Shultz gave a talk on national security. He asserted that “as a country, we need to do things that are broadly beneficial to the world.”
This philosophy extended to topics including climate change and the transition to low-carbon energy. In recent decades, Shultz became an outspoken advocate for farsighted action to address climate change. He urged the U.S. to cut its dependence on oil in favor of clean energy production, championed sustained federal support for basic research, and built bipartisan support for a revenue-neutral carbon tax proposal — ideas he advocated publicly and discussed over the years with the MIT community.
In 2007, as the Institute was launching the MIT Energy Initiative (MITEI), he became the inaugural chair of its External Advisory Board, a leadership role he held until 2019, when he chose to step down as chair. He remained a member of the board until his death, working closely with his successor and longtime friend Norman Augustine.
“George inspired those of us working on clean energy and climate change. It was a pleasant surprise when he agreed to be the inaugural chair of the MIT Energy Initiative’s External Advisory Board and, because of his enthusiasm, we didn’t need a second chair for a dozen years!” says Ernest J. Moniz, professor emeritus of physics post-tenure, thirteenth U.S. secretary of energy, and the founding director of MITEI. “I am deeply saddened by the loss of this remarkable statesman and friend.”
“Secretary Shultz was generous with his time, his wisdom, and his friendships, creating critically needed communities of shared concern — which he recognized was the way to get things done, and to have lots of fun doing so,” says MIT President Emerita Susan Hockfield. “As founding chair of the External Advisory Board of MIT’s Energy Initiative, Secretary Shultz integrated the insights of industry with the ambitions of the academy, to apply lab-based discoveries to the pressing problem of climate change. He made MITEI and MIT better, and we all enjoyed every minute of the time he shared with us.”
“George taught us much about the importance of a principled vision coupled with persistence in engaging with government on the energy and climate challenge,” says MITEI Director Robert C. Armstrong. “He also reminded us to focus on the hard problems like energy in the developing world — which led to our launch of the Tata Center for Technology and Design and other initiatives since then. We will miss him and his guidance greatly here at MITEI.”
“George Shultz is the iconic example of the contributions MIT individuals make to the country. We should honor his memory by producing many more.” says John Deutch, Institute Professor Emeritus and former U.S. director of Central Intelligence who held numerous leadership positions in the U.S. Department of Defense and U.S. Department of Energy.
Christopher Knittel, the George P. Shultz Professor of Applied Economics at the Sloan School, says, “It is a tremendous honor to hold the George P. Shultz chair, and I feel privileged to have known George, whose wit, wisdom, and statesmanship were unmatched and irreplaceable. I will miss our conversations spanning climate policy to mainstream economics research. Rest in peace, Secretary Shultz.”
Shultz authored numerous books and articles, including “Turmoil and Triumph: My Years as Secretary of State” (1993), “Learning from Experience” (2016), and “Thinking about the Future” (2019). He was an editor of “Beyond Disruption: Technology’s Challenge to Governance” (2018). His most recent book, “Hinge of History: Governance in an Emerging New World,” was published in November 2020.
Shultz’s remarkable life was built on the foundation of two long marriages. He and his first wife, Lieutenant Helena “O’Bie” O’Brien, a military nurse, met while stationed in Hawaii during the war. The couple raised five children together and were married until her death in 1995. He later married Charlotte Mailliard Swig, the City of San Francisco’s chief of protocol; they were married for 23 years until his death. In addition to Swig, his survivors include his children, 11 grandchildren, and nine great-grandchildren.
He will be deeply missed by his family, colleagues, students, and friends around the world, many of whom shared warm wishes virtually for his 100th birthday celebration in December 2020. To mark the occasion, Shultz wrote in The Washington Post about 10 things he’d learned about trust in his 100 years, underscoring the importance of developing, maintaining, and rebuilding our trust in each other. “Trust is fundamental, reciprocal and, ideally, pervasive. If it is present, anything is possible. If it is absent, nothing is possible,” he wrote. More

The temperature of a planet is linked with the diversity of life that it can support. MIT geologists have now reconstructed a timeline of the Earth’s temperature during the early Paleozoic era, between 510 and 440 million years ago — a pivotal period when animals became abundant in a previously microbe-dominated world.
In a study appearing today in the Proceedings of the National Academy of Sciences, the researchers chart dips and peaks in the global temperature during the early Paleozoic. They report that these temperature variations coincide with the planet’s changing diversity of life: Warmer climates favored microbial life, whereas cooler temperatures allowed more diverse animals to flourish.
The new record, more detailed than previous timelines of this period, is based on the team’s analysis of carbonate muds — a common type of limestone that forms from carbonate-rich sediments deposited on the seafloor and compacted over hundreds of millions of years.
“Now that we have shown you can use these carbonate muds as climate records, that opens the door to looking back at this whole other part of Earth’s history where there are no fossils, when people don’t really know much about what the climate was,” says lead author Sam Goldberg, a graduate student in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS).
Goldberg’s co-authors are Kristin Bergmann, the D. Reid Weedon, Jr. Career Development Professor in EAPS, along with Theodore Present of Caltech and Seth Finnegan of the University of California at Berkeley.
Beyond fossils
To estimate Earth’s temperature many millions of years ago, scientists analyze fossils, in particular, remains of ancient shelled organisms that precipitated from seawater and either grew on or sank to the seafloor. When precipitation occurs, the temperature of the surrounding water can change the composition of the shells, altering the relative abundances of two isotopes of oxygen: oxygen-16, and oxygen-18.
“As an example, if carbonate precipitates at 4 degrees Celsius, more oxygen-18 ends up in the mineral, from the same starting composition of water, [compared to] carbonate precipitating at 30 degrees Celsius,” Bergmann explains. “So, the ratio of oxygen-18 to -16 increases as temperature cools.”
In this way, scientists have used ancient carbonate shells to backtrack the temperature of the surrounding seawater — an indicator of the Earth’s overall climate — at the time the shells first precipitated. But this approach has taken scientists only so far, up until the earliest fossils.
“There is about 4 billion years of Earth history where there were no shells, and so shells only give us the last chapter,” Goldberg says.
A clumped isotope signal
The same precipitating reaction in shells also occurs in carbonate mud. But geologists assumed the isotope balance in carbonate muds would be more vulnerable to chemical changes.
“People have often overlooked mud. They thought that if you try to use it as a temperature indicator, you might be looking at not the original ocean temperature in which it formed, but the temperature of a process that occurred later on, when the mud was buried a mile below the surface,” Goldberg says.
To see whether carbonate muds might preserve signatures of their original surrounding temperature, the team used “clumped isotope geochemistry,” a technique used in Bergmann’s lab, which analyzes sediments for clumping, or pairing, of two heavy isotopes: oxygen-18 and carbon-13. The likelihood of these isotopes pairing up in carbonate muds depends on temperature but is unaffected by the ocean chemistry in which the muds form.
Combining this analysis with traditional oxygen isotope measurements provides additional constraints on the conditions experienced by a sample between its original formation and the present. The team reasoned that this analysis could be a good indication of whether carbonate muds remained unchanged in composition since their formation. By extension, this could mean the oxygen-18 to -16 ratio in some muds accurately represents the original temperature at which the rocks formed, enabling their use as a climate record.
Ups and downs
The researchers tested their idea on samples of carbonate muds that they extracted from two sites, one in Svalbard, an archipelago in the Arctic Ocean, and the other in western Newfoundland. Both sites are known for their exposed rocks that date back to the early Paleozoic era.
In 2016 and 2017, teams traveled first to Svalbard, then Newfoundland, to collect samples of carbonate muds from layers of deposited sediment spanning a period of 70 million years, from the mid-Cambrian, when animals began to flourish on Earth, through the Ordovician periods of the Paleozoic era.
When they analyzed the samples for clumped isotopes, they found that many of the rocks had experienced little chemical change since their formation. They used this result to compile the rocks’ oxygen isotope ratios from 10 different early Paleozoic sites to calculate the temperatures at which the rocks formed. The temperatures calculated from most of these sites were similar to previously published lower-resolution fossil temperature records. In the end, they mapped a timeline of temperature during the early Paleozoic and compared this with the fossil record from that period, to show that temperature had a big effect on the diversity of life on the planet.
“We found that when it was warmer at the end of the Cambrian and early Ordovician, there was also a peak in microbial abundance,” Goldberg says. “From there it cooled off going into the middle to late Ordovician, when we see abundant animal fossils, before a substantial ice age ends the Ordovician. Previously people could only observe general trends using fossils. Because we used a material that’s very abundant, we could create a higher-resolution record and could see more clearly defined ups and downs.”
“This is the best recent isotopic study addressing the critical question of whether early animals experienced hot early temperatures,” says Ethan Grossman, a professor of geology at Texas A&M University, who was not a contributor to the study. “We should use all the tools at our disposal to explore this important time interval.”
The team is now looking to analyze older muds, dating back before the appearance of animals, to gauge the Earth’s temperature changes prior to 540 million years ago.
“To go back beyond 540 million years ago, we have to grapple with carbonate muds, because they are really one of the few records we have to constrain climate in the distant past,” Bergmann says.
This research was supported, in part, by NASA and the David and Lucile Packard Foundation. More

State and Local Innovation Initiative seeks government partners to rigorously evaluate policies and programs aiming to address critical social issues. More

Associate professor of technology and urban planning to lead LCAU with a research focus on planning, design, construction, and retrofitting of urban environments for the 21st century. More