应我校海洋学院吴怀春教授和科学研究院李海燕副研究员邀请，Paul F. Hoffman院士来我校进行学术交流，并做学术报告。

       题目：Snowball Earth: geological evidence, numerical models and biological implications of the ultimate reversible climate extremes

       时间：2026年10月19日（星期一）14:00 –18:00

       地点： 逸夫实验楼901

       报告人简介：Paul F. Hoffman是维多利亚大学兼职教授，也是哈佛大学Sturgis Hooper地质学荣休教授。他的研究聚焦于板块构造和地球历史演化。他被广泛认为是过去100年中最具影响力和创造力的地质学家之一，是加拿大皇家学会会士、美国国家科学院国际院士（1992年），以及美国艺术与科学院国际荣誉院士（1993年）。他曾荣获洛根奖章（Logan Medal，1992年）、阿尔弗雷德·魏格纳奖章（Alfred Wegener Medal，2001年）、沃拉斯顿奖章（Wollaston Medal，2009年）、沃尔特·布赫奖章（Walter Bucher Medal，2010年）、彭罗斯奖章（Penrose Medal，2011年）以及京都奖（Kyoto Prize，2024年）。

       讲座内容：There is now compelling evidence that the world ocean was completely covered by ice shelves, hundreds of meters thick, during the Cryogenian Period (717？635 million years ago). This happened twice, 20 million years apart, and the ‘Snowball’ states lasted for a combined total of 60 million years. The continents were then mostly covered by slowly spreading ice sheets, with areas of bare frozen ground, sand-seas (ergs) and dry-valley ice-covered lakes centered on the equator. Each panglacial meltdown led to extreme CO2-greenhouse warming and extensive continental flooding. The geological evidence, the physical theories of how such events came about and were reversed, how those theories were tested with new observations, and implications for the evolution of life are the subjects of these lectures. Illustrations will be drawn from the speaker’s 30 years of Snowball-related field work on six continents, and from his new textbook, Snowball Earth in 4-G: Geology, Geophysics, Geochemistry, Geobiology, Phoenix Science Press, Nanjing, Jiangsu. The short course includes four parts:

       Lecture 1:  The global distribution of Neoproterozoic glacial deposits—synchronous or diachronous?  Association with warm-water carbonates and low paleomagnetic latitudes.  Energy-balance climate models and the ice-albedo bifurcation (tipping point).  Reversibility of a panglacial state and testable predictions of CO₂-driven self-reversal.

       Lecture 2:  Testing the predictions of a self-reversing Snowball Earth. Geochonology tests of multi-million-year duration, globally synchronous onsets and terminations, and low average sediment accumulation rates, due to weak hydrologic cycling.  Lithologic and isotopic tests of extreme postglacial CO2 greenhouse warming.  Sr isotope test for evolved Snowball ocean water.

       Lecture 3:  Dynamics of the Snowball Earth atmosphere, cryosphere and subsurface oceans. Sensitivity of continental ice sheets to warming and orbital changes.  Oxygen isotope dynamics without evaporation of seawater.  Dust dynamics, ablative ice albedo, microbial feedback, and surface meltwater production and drainage. Waterbelt states: accessibility and stability. Deglaciation and its aftermath.  Why did successive Snowball Earths differ in duration and character?

       Lecture 4:  Surface and subsurface life.  Bifurcation timescale and life in Snowball oceans.  Extant polar？alpine biomes and the Darwinian ecosystem relocation (range-shift) hypothesis.  Molecular phylogenetic tests of predicted ancestral states.  How Prochlorococcus lost its Rolex.  Snowball meltdowns and the biological ‘sweepstakes’ of ocean reoccupation. Snowball Earth causation: a two-part question.  Planetary connections: icy moons, former snowball Mars, future Snowball Earth?

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