Gordon writes:

Hello Vincent and TWIM team

I have one question and one comment pertaining to TWIM 218.

The question relates to Michael’s comment that a dry climate might make it somewhat less likely to be exposed to SARS Cov2 because the water in exhaled aerosols would quickly evaporate. This seems to imply the virus particles in the aerosols would be inactivated by the loss of water. Is this correct? I have been wondering about the role of evaporation for a while as it seems to me that after evaporation a much smaller virus particle would be left behind and that this could easily pass through a cloth mask. If the virus was still active that would be a problem.

My comment is in relation to the discussion of fungal contamination. As an industrial hygienist I have been involved in many fungal remediation projects. You definitely want to wear a proper NIOSH approved respirator, N95 or P100, not a “mask”. While it is generally true that people do not develop fungal infections unless immunocompromised it is also true that some people become allergic to fungal fragments (mycelia) and fungal spores. This can make a contaminated environment unable for them. Proper protective equipment and procedures can prevent this.



Brendan writes:

Dear Twimers,

It’s a beautiful day here in Chengdu with temperatures at 31C and some nice high scattered clouds to keep the sun at bay. I’m writing to follow up on the Mars regolith analog methanogen paper discussion. I’m just a space and biology nerd with no formal education in either and I found it was a fascinating and accessible discussion! There were a couple of points you all brought up which drove me to go and read the paper which revealed some more interesting details I want to recount here.

1. Regarding Michael’s question about whether Mars has plate tectonics, we know Mars had a geologically active past because we can see the huge Olympus Mons and numerous other inactive volcanoes on Mars’ surface. However we also have evidence that much of Mars’ recent existence has been geologically inactive and there is no evidence for a strong magnetic field like Earth’s so the current view is that Mars does not have plate tectonics now and maybe never did. The hypothesized source of water and motive for this paper is actually not deep subsurface but instead near subsurface, specifically a feature they mention called RSL or “Recurring Slope Lineae”. These features, which are seasonally appearing dark patterns on steep hillsides, were first observed in the last decade from a probe in Mars orbit and re-sparked the “we’ve found water on Mars!” debate. Arguments continue about whether the RSL are because of water or sand grain landslides but spectroscopic analysis does support water in RSLs as the result of “deliquescence of perchlorate and chlorate salts”.

2. Michael mentioned that the authors ran a control using perchlorates to inactivate the methanogens. This really caught my attention because we know from the Mars Phoenix lander and reanalysis of the Viking landers’ data that Mars soil contains perchlorates in the range of 0.5-1%. As far as I can tell from reading the paper the perchlorate used by the authors (sodium perchlorate NaClO4) was added in 30 wt% as one of two ways in order to facilitate the deliquescence conditions. The other salt used was NaCl also at 30 % wt in a different experiment which yielded methane production. In the materials and methods section the authors mention that the negative control was no salts (neither table salt nor sodium perchlorate) or water and thus no deliquescence. Since we know perchlorates can inactivate microrganisms its not surprising that the sample with sodium perchlorate at 30 wt% would not see methane production. But putting on my “reviewer #1” hat I would like to see another experiment where they can achieve deliquescence (and observe methane production or not) with a mars regolith analog that also has a 0.5-1% perchlorate content.

3. Finally regarding Elio’s pessimism about life originating on other planets I would say that we probably don’t have enough evidence one way or the other to conclude on the chances of independent origins of life. I recently read “The Origins of Life” by John Maynard Smith and Eors Szathmary which summarized scenarios for the conditions on how self replicating molecules could form cellular life. The speculation they recount makes it seem there are many possible environments (and geometries of environments) which life could have started in and we have no concrete experimental evidence for what works or not. This is different from the evolution of eukaryotes where, as I understand, we have some evidence that the symbiosis with mitochondria only happened once. On that point I’d agree with Elio: that seems like an exceedingly rare kind of event to possibly rule it out happening in life originating independently elsewhere in the universe. I read about this in Nick Lane’s book “Oxygen” which, along with “Origins of Life”, might be a bit out of date so I’m skating on thin ice and would appreciate any reading suggestions to get more up to speed on current theories for the origins of life. So in conclusion I’m more optimistic/unsure of life originating elsewhere but, if it’s exceedingly rare to get complex life which leaves unambiguous bio-signatures, then we really may be stuck for a long time not being able to know. Let the debate continue!

Thanks again for such a great podcast, keep safe, and I look forward to the next TWIMs!