December 20, 2024 — In a groundbreaking study published in Science today, an international paleontological research team led by Dr. Qing Tang and Professor Shuzhong Shen from the School of Earth Sciences and Engineering at Nanjing University has made significant advances in understandings early life evolution. By establishing the biggest paleobiology database of early Earth to date and employing cutting-edge analytical tools, including supercomputer and artificial intelligence, the research team, for the first time, constructed a high-resolution biodiversity curve spanning from 2 to 0.5 billion years ago. This study reveals that early life on Earth underwent a prolonged evolutionary journey, marked by multiple major radiations and mass extinctions before the formation of complex ecosystems around 0.5 billion years ago. This study fills a critical gap in our understanding of the macroevolution of life on early Earth, providing a theoretical basis for elucidating the origins and early evolution of life, exploring the potential for extraterrestrial life, and assessing the sustainable development of a habitable Earth.
Fossils are the most direct evidence of life’s evolution. However, when did life, particularly eukaryotes with a membrane-enveloped nucleus, originate and leave its first fossil record more than 500 million years ago? As the ancestors of all modern complex organisms, how did early life cope with environmental challenges and evolve into the diverse biosphere we see today? These fundamental scientific questions, which are crucial for understanding our origins and future, have remain largely unaddressed for a long time due to methodological limitations.
To tackle these questions, the research team spent six years developing a comprehensive paleobiology database of early Earth. By integrating big data analytical tools, such as supercomputing and artificial intelligence, Dr. Tang and his colleagues have established the first high-resolution biodiversity curve of early life.
The results indicate that the diversity of eukaryotes maintained a low but stable growth pattern since their earliest unambiguous fossil records in around 1.7 billion years ago. However, this pattern was disrupted by the emergence of a global glaciation event around 720 million years ago. Following the end of the glaciation event, life diversity began to increase rapidly and fluctuate frequently, leading to multiple episodes of major biological radiation and extinction. These include a significant biological radiation event between approximately 635 and 580 million years ago, followed by the first mass extinction event in life history, which results in the sharp disappearance of the dominant organism--spiny microorganisms. Following this mass extinction, more complex macroscopic organisms, including animals, underwent rapid radiation. However, these complex macroscopic organisms encountered two significant declines in diversity at the end of the Ediacaran Period (approximately 551 to 539 Ma), marking the earliest two mass extinction events in the evolutionary history of animals.
This study, by using big data analyses, quantitatively illustrate for the first time the first 1.5-billion-year evolutionary journey of fossilizable eukaryotes on Earth. It delineates the early history of complex life, including its origins, radiation, extinction, re-radiation, and the eventual formation of modern-like ecosystems. The findings suggest that extreme climate events, such as global glaciations, severely disrupted the evolutionary trajectory of Earth's early biosphere, leading to mass extinction events. Following the end of glaciation events, the subsequent warming of surface temperatures and rise in atmospheric oxygen levels facilitated new radiations of increasingly complex organisms. This further confirms that the evolutionary pattern of life from simple to complex is not a straightforward linear process, but rather an alternating pattern of prolonged stagnation and relatively rapid radiation. This study also highlights the profound impact of abrupt environmental changes, such as fluctuations in surface temperature and oxygen levels, on the evolution of early complex life systems, providing valuable insights for scientists exploring extraterrestrial life in extreme environments and assessing the future habitability of Earth.
Reviewers for Science commented that “this is, in many respects, a long overdue paper to examine the fossil record of the Proterozoic; This is a huge achievement; there will be a plethora of papers following publication of this paper doing just that.”
This study was supported by the National Key Research and Development Program of China, the National Natural Science Foundation of China, and the IUGS Big Science Project—Deep-time Digital Earth (DDE).
High-resolution biodiversity curve on early Earth
Link to the paper:
https://doi.org/10.1126/science.adm9137
