Late paleozoic climate revealed by coral fossil patterns

Conclusion Our study of growth line width from fine coral fossils obtained important clues of Carbonifer- ous period paleoclimate. Based on a detailed analysis of the growth increment of coral epithe- lium during the Carboniferous period, the following conclusions are drawn: 1. The hypothesis “the measurement of the width of the growth line can reflect the changes in solar day length” is again supported with new materials in this study. 2. The bimodal phenomenon of the growth line width of warm-water individual coral fossils in the Late Carboniferous period is positively correlated with the sunshine duration. Confi- dence interval analysis shows that the credibility of this result is above 95%. 3. The climate of Shiqiantan in the Late Carboniferous period was similar to that of modern North China, and there was a rainy season. 4. The seasonal changes in Shiqiantan area in the Late Carboniferous period were evident. Thus, the obliquity of the ecliptic, which causes Earth’s seasons, has already existed for at least 300 million years. In the supporting documents, we conducted a theoretical simulation of the sunshine variation calculated based on a 38˚ obliquity of the ecliptic, and the simula- tion results did not contradict the experimental observations. After all, this is a preliminary study and should be regarded as an attempt. Further studies may either focus on dynamics or a search for new material. Although the dynamics of these materials are still being debated, they could provide an even longer time span for testing. Supporting information

S1 File. Detailed methods and measurements. (PDF) S2 File. Specimen details. (PDF) S3 File. Confidence interval analysis. (PDF) S4 File. Effects of obliquity of the ecliptic and precipitation on sunshine duration during the Late Carboniferous. (PDF) Acknowledgments We would like to thank Professor Shuhai Xiao from the Department of Geology at Virginia Tech and Professor Yuanlin Sun from the Department of Geology at Peking University for their support. We would also like to thank Miss Yuan Zheng from Shaoxing University for helping with the revision. The research samples are stored in the Institute of Paleontology, Peking University.No permits were required for the described study, which complied with all relevant regulations. Author Contributions Conceptualization: Weijia Zhang. Data curation: Jiaju Li. PLOS ONE Late paleozoic climate revealed PLOS ONE | https://doi.org/10.1371/journal.pone.0290127 August 15, 2023 11 / 13