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Sanjoy Som, David Catling , Jelte Harnmeijer , Peter Polivka , Roger Buick

Air density limited 2.7 billion years ago limited to twice present levels by fossilized raindrop imprints. Sanjoy Som, David Catling , Jelte Harnmeijer , Peter Polivka , Roger Buick Earth and Space Sciences and Astrobiology Program University of Washington.

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Sanjoy Som, David Catling , Jelte Harnmeijer , Peter Polivka , Roger Buick

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  1. Air density limited 2.7 billion years ago limited to twice present levels by fossilized raindrop imprints Sanjoy Som, David Catling, JelteHarnmeijer, Peter Polivka, Roger Buick Earth and Space Sciences and Astrobiology Program University of Washington

  2. Atmospheres are a window to the planet

  3. Atmospheres: a window to the planet Kasting, Sci. Am., 2004

  4. Early Earth Atmosphere: poorly constrained • Greenhouse forcing: which gases and how much? Kasting, Sci. Am., 2004

  5. Early Earth Atmosphere: poorly constrained • Greenhouse forcing: which gasses and how much? Kasting, Sci. Am., 2004 Would be nice to know the pressure…

  6. Using imprints to infer atmospheric density was first suggested by Charles Lyell in 1851 “From such data we may presume that the atmosphere of one of the remotest periods known in geology corresponded in density with that now investing the globe, …” Charles Lyell, Proceedings of the Geological Society, 1851.

  7. Thin section Scale bar: 5 mm

  8. ~sea level + semi arid environment

  9. Maximum raindrop size is independent of air density Vuillermaux and Bossa, Nature Phys. 2009 Mathews and Mason, 1964 Clift et al, 1978

  10. Raindrop imprint – air density puzzle Given that maximum raindrop size is independent of air density, Given that raindrop impact momentum controls imprint size, I. What is the relationship between impact momentum and imprint size in volcanic ash? II. How does raindrop impact momentum change with air density?

  11. Impact momentum controls imprint size Huang et al. 1983

  12. A dozen imprints per drop size Imprints in 10% moist (by mass) ash

  13. Imprints were measured with 3D laser scanner High-resolution 3D laser scanner (vertical accuracy: 0.0002”)

  14. Relationship between imprint size and impact momentum Som et al. 2012

  15. Impact momentum is obtained from first principles Lorenz, 1993 Som et al. 2012

  16. Air density depends on what raindrops size created the largest imprints Som et al. 2012

  17. Assume that semi-arid modern rainfall statistics apply to the early Earth 99% 78% Lebel et al. 1997 When the imprints were formed, rainfall fell at a rate < 100 mm hr-1 with a probability of 78%-99%

  18. Assume that largest imprints were formed by largest raindrops Binning algorithm: Scott, D. On optimal and data-based histograms, Biometrika, 1979 0.2 % of total Som et al. 2012

  19. Raindrop size distribution and rainfall rate are related by empirical relationships 0.2 % of total R4 = 100 mm hr-1 Som et al. 2012(after Willis and Tattelman, 1989) Som et al. 2012

  20. Maximum raindrop diameters were between 3.8mm and 5.3mm with 78%-99% probability Som et al. 2012

  21. Air density was between 0.6 kg m-3 and 1.3 kg m-3 with 78% - 99% probability Som et al. 2012

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