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The importance and role of hydrothermal vents and underwater volcano

Hydrothermal vents and the origins of life By Rachel Brazil16 April 2017 No comments Debate rages between biologists and chemists over whether life began on land or under the sea. But there is still no consensus as to the environment that could have fostered this event. With several hypotheses in play, the race is on to replicate the conditions that allowed life to emerge. In 1977, the first deep sea hydrothermal vent was discovered in the East Pacific Rise mid-oceanic ridge.

This was followed in 2000 by the discovery of a new type of alkaline deep sea hydrothermal vent found a little off axis from mid-ocean ridges. The first field, known as the Lost City, was discovered on the sea floor Atlantis Massif mountain in the mid-Atlantic. The vents are formed by a process known as serpentinization. Seabed rock, in particular olivine magnesium iron silicate reacts with water and produces large volumes of hydrogen.

This mirrors the way that cells harness energy. Cells maintain a proton gradient by pumping protons across a membrane to create a charge differential from inside to outside.

Discovering Hydrothermal Vents

Known as the proton-motive force, this can be equated to a difference of about 3 pH units. This energy, along with catalytic iron nickel sulfide minerals, allowed the reduction of carbon dioxide and production of organic molecules, then self-replicating molecules, and eventually true cells with their own membranes.

Chemical gardens Chemist Laura Barge, also a research scientist at JPL, is testing this theory using chemical gardens — an experiment you might have carried out at school.

The classical chemical garden is formed by adding metal salts to a reactive sodium silicate solution. The metal and silicate anions precipitate to form a gelatinous colloidal semi-permeable membrane enclosing the metal salt. This sets up a concentration gradient which provides the impetus for the growth of hollow plant-like columns. To mimic the early ocean she has injected alkaline solutions into iron-rich acidic solutions, making iron hydroxide and iron sulfide chimneys.

From these experiments her team have illustrated that they can generate electricity: Nick Lane, a biochemist at University College London in the UK, has also been trying to recreate prebiotic geo-electrochemical systems with his origins of life reactor.

What is a hydrothermal vent?

For example, minerals such as greigite Fe3S4 are found inside vents and they show some relationships to the iron—sulfur clusters found in microbial enzymes.

They could have acted as primitive enzymes for the reduction of carbon dioxide with hydrogen and the formation of organic molecules. On one side of a semiconducting iron—nickel—sulfur catalytic barrier, an alkaline fluid is pumped through to simulate vent fluids and on the other side, an acidic solution that simulates sea water.

As well as flow rates, the temperatures can be varied on both sides. They are working on replicating their results and proving that the formaldehyde seen is not coming from another source such as degradation of tubing.

From the same conditions, Lane says they have also been able to synthesise low yields of sugars, including 0. Digging deeper Investigating hydrothermal vents, geochemist Frieder Klein from Woods Hole Oceanographic Institution in the US has discovered a variation on the deep sea origin story. He has found evidence of life in rock below the sea floor which might have provided the right environment for life to start.

  • Fortunately, the challenges of extreme deep-sea exploration have led to tight collaboration between marine scientists and engineers and the emergence of a variety of enabling technologies driving these new discoveries;
  • Exploration enablers Finding vent systems in diverse oceanic environments takes curiosity, determination, and, well, guts;
  • But the deep sea hydrothermal vent camp is not ready to throw in the towel just yet.

The samples came from rock 760m below the current sea floor, which would have been 65m below the early unsedimented ocean floor. He saw some unusual looking veins in the samples, composed of minerals also found at the Lost City hydrothermal system. This suggests similar chemistry could be going on below the sea floor. He suggests the desiccating properties of the mineral brucite Mg OH 2 might explain the preservation of organic molecules from the microbes.

These included amino acids, proteins and lipids which were identified by confocal Raman spectroscopy. Klein says he was initially sceptical, but analysis of extracted samples confirmed unique lipid biomarkers for sulfate-reducing bacteria and archaea, which are also found in the Lost City hydrothermal vents system. Armen Mulkidjanian at the University of Osnabruck in Germany says there are several big problems with the idea, one being the relative sodium and potassium ion concentrations found in seawater compared to cells.

Mulkidjanian invokes what he calls the chemistry conservation principle — once established in any environment, organisms will retain and evolve mechanisms to protect their fundamental biochemical architecture. He says therefore it makes no sense for cells that contain 10 times more potassium than sodium to have their origins in seawater, which has 40 times more sodium than potassium.

His assumption is that protocells must have evolved in an environment with more potassium than sodium, only developing ion pumps to remove unwanted sodium when their environment changed.

  • The first field, known as the Lost City, was discovered on the sea floor Atlantis Massif mountain in the mid-Atlantic;
  • The seafloor is dynamic, and an eruption had paved it over sometime in the ensuing 25 years;
  • Underwater volcanoes at spreading ridges and convergent plate boundaries produce hot springs known as hydrothermal vents;
  • Hydrothermal vents form at locations where seawater meets magma;
  • Since then, hundreds of vents have been discovered across the global ocean , from Antarctica to the Arctic , along with an estimated eight hundred vent animal species and countless microbial species.

Mulkidjanian thinks life could have sprung from geothermal systems, such as the Siberian Kamchatka geothermal fields in the Russian Far East. It is only pools created from vapour vents that have more potassium than sodium; those formed from geothermal liquid vents still have more sodium than potassium.

A handful of such system exist today, in Italy, the US and Japan, but Mulkidjanian suggests that on the hotter early earth you would expect many more. David Deamer of the University of California Santa Cruz in the US has been studying macromolecules and lipid membranes for over 50 years.

The Discovery of Hydrothermal Vents

One of the biggest arguments against a deep sea origin is the fact that so many macromolecules are found in biology. Wet and dry cycling occurs every day on continental hydrothermal fields. This allows for concentration of reactants as well as polymerisation. The assumption that natural selection is incapable over 4 billion years of coming up with an improvement I think is mad Deamer has been trying to create his own protocells in the lab — by mixing lipids and RNA components adenosine monophosphate and uridine monophosphate.

When dried, the lipids self-assemble into membrane-like structures, and if nucleotides are trapped between lipid layers they will undergo esterification to produce RNA-like polymers. But the deep sea hydrothermal vent camp is not ready to throw in the towel just yet. Barge says the vent environment could allow for concentration of reactants and condensation reactions. Seeing the light One other point of contention is the presence or absence of ultraviolet UV light.

This could be a strong influence in a terrestrial origin scenario with no protective ozone layer on the early earth, but completely absent in the deep sea theory.

Synthetic chemists generally favour a continental origin and geologists and biologist mostly deep-sea hydrothermal vents. So is there a way to unite the disciplines? Further evidence to support the origins of life in deep sea hydrothermal vents centres on showing a plausible set of metabolic steps leading to complex molecules. At JPL, they are looking at how amino acid behave in their chemical gardens, according to Barge.

But says Lane the big problem of the thermodynamic driving force is solved by hydrothermal vents. Panspermia — the theory that life was seeded from space, seems eccentric, but not everybody counts it out.

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Whether this is the case or not, life elsewhere is certainly feasible. In the next five years, Nasa is planning to send a spaceprobe to both these moons to look for signs of life. Understanding our own origin story could help us work out where to look.