Deep Sea Holds Relics of the Earliest Life on Earth

March 30, 2006

The microbes that inhabit deep-sea hydrothermal vent environments may be relics of the earliest life on Earth.

Some of the most arresting images of life on our planet have come from the deep-sea world of hydrothermal vents. Massive chimneys belching superheated fluids, colonies of giant crimson-tipped tubeworms swaying in the current, swarms of tiny shrimp, albino crabs.

These ecosystems, although isolated from life on the surface, contain a virtual zoo of creatures, thriving under conditions of heat and pressure so extreme that, until the vent communities were discovered in the late 1970s, scientists did not even imagine that they existed.

Perhaps even more fascinating – at least to biologists – has been the cataloging of the microbial life that flourishes in the scalding vent fluids, the organisms at the bottom of the vent-community food chain. DNA analysis of these microbes has revealed that they represent some of the planet’s oldest forms of life. This has led some researchers to speculate that, some four billion years ago, life on Earth may have had its origin in similar vent environments.

Studying these microscopic life forms, even simply finding out what microbes are there, is a challenge. Using submersible vehicles, scientists have managed to recover samples from the vents, and to bring them to the surface for laboratory study. But while this approach has made it possible to produce a series of snapshots of microbial vent populations, it has not enabled scientists to develop a dynamic view of how these communities change over time: how they respond to seasonal changes in ocean currents, for example, or to catastrophic events such as earthquakes and sea-floor eruptions.

Physical sensors – thermometers, simple chemical detectors – enable researchers to monitor, in real time, changes in seawater temperature and chemistry. But to learn about what microbes are present in an environment, scientists must use DNA-analysis tools that are far more complex than a thermometer.

These tools, designed for use in sophisticated biomedical laboratories, have not been adapted for use in the briny deep. So, until now, marine scientists have not been able to observe how deep-sea microbial populations change over time.

Trying to understand the dynamics of the environment with the tools available, says Chris Scholin, is like “trying to predict the weather. But you get to look out your window once a month in one direction – and that’s it. It’s really hard to then come up with a comprehensive view of what’s happening and how the weather is working.”

Scholin chairs the science department at the Monterey Bay Aquarium Research Institute (MBARI), in Moss Landing, California. He has been working for many years to develop an Environmental Sample Processor (ESP), a set of diagnostic tools adapted from the biomedical industry, packed into a submersible cylinder about the size of an oil drum and operated by remote control. He recently received funding from NASA’s ASTEP(Astrobiology Science and Technology for Exploring Planets) program to further develop ESP. ASTEP promotes the development of technologies that could prove useful in the search for life on other worlds.

Scholin plans to lower an ESP unit to the ocean floor, and by remote control, direct it to collect samples, prepare them for analysis, pass them to miniaturized test units (known as a “pucks”), and report the results. Pucks are small self-contained test devices about the size of a quarter and half an inch thick. Each puck can be configured internally to perform a specific analytical test.

One of Scholin’s critical tasks will be to develop a deep-sea version of the ESP (D-ESP). Collecting samples deep in the ocean presents unique problems because pressure increases with depth. It is impractical to vary the internal pressure of the pucks to match that of the surrounding seawater, so samples collected at depth need to be de-pressurized before they are passed to the pucks to be analyzed. Injecting high-pressure samples into the low-pressure pucks would blow up the test equipment.

The first field test of the D-ESP will take place this fall in the Monterey Bay, at a depth of 1,000 meters (more than 3,000 feet), where the pressure is nearly 1,500 pounds per square inch (psi), 100 times what it is at sea level.

Ultimately, Scholin’s team will install a D-ESP unit at a depth of 4,000 meters (nearly 2.5 miles). The pressure there is close to 6,000 psi. That’s equivalent to the weight of four full-sized pickup trucks pressing down on a Jell-O cube.

The first field test is intended primarily as a proof of concept. During the second field test, Scholin will install a D-ESP at a cold methane seep in the Santa Monica Basin, where frozen methane hydrate on the sea floor furiously bubbles out gas into the surrounding ocean, much as dry ice bubbles when dropped into water.

Less well known than hydrothermal vents, cold seeps also support rich and diverse communities of organisms. Scientists will “fly” the D-ESP back and forth between background seawater and the methane-enriched water above the seep, to compare the two microenvironments.

In the third and final field season, in 2008, a D-ESP unit will be installed on the ocean floor in the Juan de Fuca Ridge and left there for a full year, to study dynamic changes in the microbial population. There are three types of microbes present in and around hydrothermal vents: background organisms, which are always present; responders, which “bloom” in the presence of a chemically enriched hydrothermal plume; and (some scientists contend) subsurface organisms, which are expelled during volcanic or seismic explosions. Scholin and his colleagues will then instruct the ESP to perform a series of tests to ascertain how these three populations respond.

“The notion was to have an instrument system that could sit in an area of geomicrobial interest for an extended period of time, and determine if we could actually resolve those different groups by taking our sampling queues from these other contextual sensors,” Scholin says.

Although ASTEP’s mission is to further the development of technology for use in interplanetary missions, Scholin says NASA “would not likely take the exact diagnostic procedures that we employ for our studies and send them to Europa” or another world. Rather, it’s the total process – remote identification, acquisition, preparation and testing of a sequence of samples – that might inspire designers of future missions. ESP technology, says Scholin, could even be adapted for use on a rover exploring the frozen wastes of Mars.

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