She is rooted in isotope geochemistry and is determined to explore habitable planets outside the earth!

In the vast universe, various elements are constantly being generated and destroyed, forming a complex element cycle process. According to the Big Bang theory, at the time of the universe's origin, there were only light elements such as hydrogen and helium in the high temperature and high energy environment, which provided the basis for the origin and evolution of the universe. As the universe evolved, more elements were synthesized through nuclear fusion reactions inside stars, thus enriching the element spectrum in the universe. The isotopic composition and distribution of these elements are crucial to understanding the evolutionary history of the universe and the earth.

So, in the vast universe, are there any habitable planets like Earth? All this is inseparable from the theoretical basis provided by isotope geochemistry.

▲ Zhang Pu In order to explore this mystery, Zhang Pu, a researcher at the International Research Center for Planetary Sciences of Chengdu University of Technology, has rooted her research in the development of isotope geochemistry and chronology methods and their applications in earth and planetary science research, and has carried out a series of scientific research explorations. For more than ten years, she has connected her research into a complete spectrum, taking it as her responsibility to develop technologies urgently needed for global climate and environmental changes in China or to break through current technological bottlenecks, actively practicing related scientific research work, and using it to serve the research of surface geochemistry and planetary science of the Earth system.

Taking root and consolidating the scientific research foundation step by step

Geological processes reflect the laws of the earth. Since ancient times, geological research has been closely related to human survival. Zhang Pu's understanding of geology was established at Northwestern University.

The Department of Geology at Northwest University was founded in 1939 and is one of the earliest comprehensive university geology departments in my country. During her four years of undergraduate study, Zhang Pu came into contact with many outstanding scholars in related fields and laid a solid foundation in geology under their guidance. Today, Zhang Pu still feels very emotional when she recalls her time studying at Northwest University. "Many times when research reaches a certain level, you will find that you have returned to the undergraduate textbooks. And in the future, when you want to achieve a breakthrough from 0 to 1, you will find that these foundations are extremely important." She said.

Zhang Pu's undergraduate studies made her more interested in geology. At that time, she made up her mind to continue her studies in geology and uncover more scientific mysteries in this field through exploration. Driven by her interest, after graduating from undergraduate studies in 2005, Zhang Pu was successfully admitted to the Institute of Earth Environment of the Chinese Academy of Sciences to pursue a master's degree and a doctorate in Quaternary geology.

The theory of the four glacial periods in the Quaternary Period established in Europe in the late 19th and early 20th centuries had a wide-ranging impact on the study of glaciation, climate change and other aspects. Since the 1950s, the application of radiocarbon dating, potassium-argon dating, uranium series dating, fission track dating and oxygen isotope thermometry has brought Quaternary geological research to a new level. Zhang Pu's master's and doctoral studies at the Institute of Earth Environment, Chinese Academy of Sciences laid a solid foundation in the field of isotope geoenvironment. With the support of increasingly profound scientific research accumulation, she hopes to make more representative scientific research results in related fields.

Deepen cultivation and innovate isotope geochemistry research

There are no shortcuts in scientific research. We can only keep looking for new evidence and let facts speak for themselves. This is especially true in the field of isotope geochemistry.

In Zhang Pu's view, the Earth has gone through more than 4 billion years of coordinated evolution of geology, environment, climate, and biology. Looking back at the history of the Earth from today's perspective, the generation of some geological elements, the differentiation of river surface, and the changes in environmental parameters are all relevant evidence for studying Earth science, and many scientific principles of these research directions are still common in the field of planetary science research. For Zhang Pu, using these theoretical foundations to solve scientific problems in a completely unknown field is still extremely exploratory and innovative.

In the more than ten years since he graduated with a doctorate, Zhang Pu's scientific research has spread to many universities at home and abroad, and he has carried out a series of innovative scientific research explorations in the geochemical behavior of uranium and thorium in the surface weathering process of the basin, geological environment and climate change, high-precision carbonate U-Th, U-Pb chronology, and water body chronology.

From November 2014 to January 2017, Zhang Pu was engaged in postdoctoral research at the Department of Geology at the University of Minnesota in the United States, where he first came into contact with uranium-thorium geochronology. Uranium and thorium are lithophile elements that are widely present in the earth's crust. Weathering of bedrock makes them widely involved in various geochemical processes in the surface and near-surface environment. The uranium series dating method was developed by geologists and was originally used to determine the age of rock formations such as stalactites and stalagmites in caves. When water seeps out of the cave, it carries extremely low concentrations of dissolved radioactive substances such as uranium and mineral calcium carbonate. Over time, the radioactivity of uranium gradually decays and turns into another element, thorium. The related technologies of uranium-thorium geochronology have very important scientific value and application prospects for paleoclimate, paleoenvironment and the development of related resources.

After returning to China, Zhang Pu continued his research in this direction at the Institute of Global Change at Xi'an Jiaotong University. He innovatively applied the carbonate U-Pb method to the U-Pb absolute dating of stalagmites and tooth fossils, providing important technical support for promoting the study of Early Quaternary paleoclimate and paleoenvironment in my country, and making it possible to establish high-resolution paleoclimate records.

In the National Natural Science Foundation project "High-precision and High-resolution Dilution U-Pb Chronology of Carbonates in Sanbao Cave Stalagmites since the Quaternary" hosted by Zhang Pu, she established a U-Pb dilution dating method suitable for stalagmites samples after a series of conditional experiments and optimization of instrument parameters to address the technical difficulties of low-content high-precision carbonate dilution U-Pb dating. It is expected that the accuracy of stalagmites since 2.5Ma will reach 2000-2400 years, and it will be used to construct a high-resolution chronology framework for stalagmites in Hubei Sanbao Cave since the Quaternary. "The entire research process of this project is a process of gradually improving the past and the present. In the future, it can be applied to the prediction of climate change, and provide theoretical and technical support for paleokarst, environment and life evolution." Zhang Pu said.

In addition, Zhang Pu is also the advocate and practitioner of the innovative application of uranium-series isotopes to the evaluation of paleo-weathering history and lake chronology of lakes in the Qinghai-Tibet Plateau for the first time. The Qinghai-Tibet Plateau is the region with the most lakes in China. The lakes here are less disturbed by human activities and are mainly affected by glacier melting and evaporation caused by climate change. It is an intuitive and sensitive reaction area to climate change. Therefore, the study of changes in lakes on the Qinghai-Tibet Plateau has far-reaching significance for the study of regional and even global climate and environmental changes. With the development of science and technology, uranium-series dating techniques have gone through different stages of development, and these techniques have made certain contributions to the evaluation of paleo-weathering history and lake chronology of lakes in the Qinghai-Tibet Plateau at different times and stages. Through research in this direction, Zhang Pu hopes to not only better evaluate the current problems of lakes in the Qinghai-Tibet Plateau, but also lay a better foundation for studying the future evolution of climate and environment.

Practice and integrate research with new directions

Although the road is long, if you keep walking you will reach your destination; although the task is difficult, if you keep working you will succeed. Zhang Pu's scientific research results are all born out of years of scientific research practice. "I remember when we went to the salt lake to collect samples, our car had to go around a large saline-alkali land to reach the research site. Because the ground was muddy and slippery, the vehicle had to rotate 360 ​​degrees and could hardly stop." Zhang Pu said that these precious scientific research practice experiences not only honed her will and mind, but also made her more respectful of scientific research, thus giving her more courage to overcome difficulties.

In Zhang Pu's opinion, the most difficult time in scientific research may be when everyone involved has no answer, but this process from 0 to 1 is the most fascinating. In Zhang Pu's life journey, she is still meeting different challenges and creating more possibilities.

In July 2022, Zhang Pu came to work at the International Research Center for Planetary Science at Chengdu University of Technology. Here, while continuing her previous research work in the fields of isotope geochemistry and chronological method development, she is also combining related research with the application of planetary science research. Although Zhang Pu was a little uncomfortable with the initial transition from isotope geochemistry to planetary-scale research, as the research progressed, she found the perfect fit between the two studies and carried out many innovative explorations.

In the future, Zhang Pu will search for habitable planets outside the Earth from the perspective of continental weathering of habitable planets and the co-evolution of climate, environment and organisms. Zhang Pu said: "From the early formation of the Earth to the present, the phenomenon of continental weathering has always existed, and current research has found that the nutrients produced by continental weathering are inevitably related to the origin of life." In the future, she will start from this perspective and use U and Th isotopes to trace surface processes and dust fluxes, trace the redox characteristics of the Earth, trace the U migration and transformation mechanism of the freeze-thaw process, and study the planetary evolution process. In the direction of the co-evolution of climate, environment and organisms, she will reveal the evolution of water bodies on the surface of habitable planets, find new breakthroughs for related scientific issues, and provide scientific research evidence for the selection of suitable habitable planets in the future.

A journey of a thousand miles begins with a single step. Zhang Pu has been working in the field of geology for more than 20 years since she started her research in 2001. Today, she is still moving forward with the same passion to explore deeper and broader areas of isotope geochemistry and planetary science.