DS Michaels writes: ====== Hoffman's general approach on CO2 flows is described at http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002AGUFM.P51B0354H&; db_key=AST&high=4061e3e63a18001>>
This paper speaks of catastrophic outflows that can produce sudden torrents of supercritical CO2 that could, under just the right circumstances, produce the braided and cut channels we see on Mars. I seen nothing whatsoever that suggests pools of liquid CO2 could have existed long enough to produced layer bedrock, salt deposits et al. ====== Hoffman's general approach doesn't include all his specific thinking on White Mars. I distinctly recall seeing Hoffman sketch a scenario of a high-density (if short-lived) CO2 atmosphere with pressures strong enough to keep liquid CO2 bodies on the surface in liquid phase. Annoyingly, at the moment, his site is down, and I can't find the keywords for a Googlecache version. I can't speak to the issues of layer bedrock or salt deposits. Layer bedrock doesn't seem implausible with a liquid CO2 surface environment, if it lasts long enough. Salt deposits? My geochemistry is vestigial at best. Hoffman's main argument rests on the lack of surface carbonates, and I haven't followed the news from Mars closely enough to know whether that picture has changed. BTW, Hoffman has never said that life is so terribly unlikely even in a White Mars scenario, since subsurface environments might be hospitable enough. Nor do I see White Mars in itself being exclusive of Warm Wet Mars periods. The occasional collision might have released a lot of CO2 and particulates, warming Mars for relatively short, but formative, periods of time, keeping H2O in the atmosphere and/or precipitating long enough to make a difference. We may be looking at a planetary surface in which CO2 gas flows AND CO2 liquid flows AND H2O liquid flows have all played roles at different times. After all, it wasn't so long ago that glaciers were finally recognized as having significantly changed parts of the earth's surface. I can't remember anyone talking about glacial activity on Mars at some point, but why not? It takes all kinds (of phases and substances) to make a world. And whatever Mars is, it's a world - not just a spherical rock with some frosting on the top and bottom. Hoffman is a petro guy, he comes late to astronomy and planetary studies. It's perhaps tempting to take potshots at mainstream theory in another field, while safely ensconced in your own. On the other hand, Alvarez & Son came from halfway outside the field of evolution and extinction (Luis definitely from outside), but now the idea that a big collision killed the dinosaurs has become the accepted wisdom (even if more recently under attack again.) Sometimes the voices from outside are right, or at least helpful in breaking up theoretical logjams. -michael turner [EMAIL PROTECTED] == You are subscribed to the Europa Icepick mailing list: [EMAIL PROTECTED] Project information and list (un)subscribe info: http://klx.com/europa/
