Lost City Hydrothermal Field

Most of us have seen a black smoker before, that’s one in the picture. While it does provide resources for the web of life around it, that ecosystem is not entirely independent from sunlight. To begin with, let’s see what makes up a black smoker.

Most of them lie in a geologically active region where crusts are thinner. Water that have seeped in through faults are heated up by magma, and shoots up from the crusts at 400 degC (it doesn’t boil because of the large pressure). This water is acidic (pH < 3), which means that it can dissolve metal sulfides from¬† magma and bring it up above the seabed. Upon contact with seawater (~ 2 degC), the solutes precipitates and form the structures we see.

The schematic shows this pretty clearly, except that I don’t really have a clue where helium comes from. Looking at this cycle alone, it seems to be a one way process of depositing materials below the crust to above. REE stands for Rare Earth Element like scandium and yttrium.

Our next concern is how life functions in such an ecosystem. From ESE3301 we know that archae and extremophiles have adapted to thrive.  Some examples are methanotrophs and thermosulfobacteria. More complex lifeforms such as tube worms feed on these organisms, and when they themselves die, they re-deposit the minerals back to the system, thus closing the life cycle. While this sounds self-sustainable, some microbes that support the giant tube worms require both sulfide and oxygen; and the source of oxygen comes from photosynthetic organisms far above.

So, what so interesting about the Lost City Hydrothermal Vent? That life there seems to be completely independent of sunlight.

Calcium Carbonate Chimneys

Calcium Carbonate "Chimneys"; Without metal sulfides, there is no "black smoke"

LCHV is located near the mid-Altantic ridge, the line cutting across the Atlantic where the Eurasian plate and North American plate diverges. While water sprouts up similarly, the highest recorded temperature is only 90 degC, and it is alkaline (pH 9-11). Instead of metal sulfides, it is rich in calcium, which means the “chimneys” are mainly limestone. The chemistry here is clearly different.

Adding on, a reaction called serpentinization causes the water to become highly reduced: all the oxygen has been stripped and replaced with energy-rich gases like hydrogen, methane and sulfide. There is then little surprise one third of the microbes at Lost City methanogens that metabolizes hydrogen. The surprising thing is that Lost City methanogens operate independently of the sun.

The significance of all this (together with several other supporting evidence) suggests the possibility of life originating at a hot spring ecosystem akin to Lost City. Interesting stuff huh.

(Source: Wikipeida and Scientific American Dec 09)

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