Thread by @mike_malaska

@mikamckinnon @SiO2moyer @justinboldaji Carlsbad and Lechuguilla Caves have a really wierd and fascinating geology history. They were made by bacteria!

@mikamckinnon @SiO2moyer @justinboldaji The story goes like this. Gypsum laid down. Then...thick thick limestone laid down on top of that. Way way down deep, microbes eat gypsum, H2S bubbles up. (Microbes reduce sulfate). ((there might be other ways H2S bubbles up.)) That gets H2S percolating up into the limestone.

@mikamckinnon @SiO2moyer @justinboldaji Then, up higher in the limestone layers, there are places where oxygen in water mixes with H2S charged waters. Some bacteria love this! They can eat H2S in the water and combine with O2 in the water and get energy!!!
They pee out sulfuric acid! (H2SO4)

@mikamckinnon @SiO2moyer @justinboldaji Wanna see what those bacteria look like? A big colony looks like this!
(Cueva de Villa Luz, Mexico)
((My finger for scale))
flic.kr/p/iCNnPv

@mikamckinnon @SiO2moyer @justinboldaji So that sulfuric acid converts limestone to gypsum. Gypsum is weaker, and more soluble! It just eats away at the cave! Is quick.
Here's a pic of what that might've looked like when it happened. (Again Cueva de Villa Luz)
((For details see photo info))
flic.kr/p/iz6NPn

@mikamckinnon @SiO2moyer @justinboldaji ((OK. Is there an alien life or #Astrobiology angle here? Yeah these bacteria make cool patterns on walls. Biovermeculation patterns.)) We saw hese in Cueva de Villa Luz. Check this out:
flic.kr/p/iEFAmj))

@mikamckinnon @SiO2moyer @justinboldaji ((so we should have a way of looking for those biovermeculation patterns in caves on other worlds, like on Mars or Saturn's moon Titan.))

But..back to geology story of Carlsbad caves...

@mikamckinnon @SiO2moyer @justinboldaji So you got limestone, H2S, oxygen from surface water, and bugs peeing out sulfuric acids that chemically opens up the cave.
During this time cave is chemically eroding. Getting bigger quickly.

@mikamckinnon @SiO2moyer @justinboldaji At some point. It stops. Maybe a hole opens up and H2S escapes easily, or deep H2S production just stops. No more bacteria peeing acid, no more cave opening. It just sits there as big underground void. But not for long...

@mikamckinnon @SiO2moyer @justinboldaji Water still percolating down from above. Slowly dissolves limestone (plant roots help - biology again!) As limestone charged water gets to cave carbon dioxide releases, limestone deposits*. And you get pretty cave formations.

*chemistry, but also maybe biology too...

@mikamckinnon @SiO2moyer @justinboldaji Here's a cute little limestone deposit growing in side corner of an actively growing sulfide cave. That side corner had strangely neutral water chemistry.
flic.kr/p/iC2AsZ

(My contribution to expedition was helping map the water chemistry in that cave.)

@mikamckinnon @SiO2moyer @justinboldaji So this would have looked like the start of all those cool formations in Carlsbad and Lechuguilla. Voids. Then reprecipitation. This clear pool is slowly and beautifully precipitating minerals (mostly carbonate, but Lechuguilla has lots of fun diverse chemistry) around basin.

@mikamckinnon @SiO2moyer @justinboldaji Each pool might have its own special mix of nutrients and concentrations. Could have different types of bacteria in each one. May have been isolated for a long time, so each pool is like it's own little world.

@mikamckinnon @SiO2moyer @justinboldaji So by studying these microbes, we can understand more about underground life on Earth. And maybe also learn about life we find on other worlds. Are there places on Mars or Ceres that might have or had these same conditions? Did microbes live there? How would we detect it?

@mikamckinnon @SiO2moyer @justinboldaji If you are interested and want to see pix with some details in the caption. I have a Flickr album of a scientific expedition to a sulfide cave in southern Mexico - the snotite cave).
Link here: flic.kr/s/aHsjPoQ7Lc

(Many of those scientists also research Carlsbad)