Resource: Deep-Sea Vents and Life's Origins

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Seafloor spreading generates new ocean crust, but it may also have created conditions necessary for the beginning of life on Earth. At mid-ocean ridges, molten lava pushes through breaks in the crust during amazing undersea volcanic eruptions. This molten rock quickly cools, and as it does, it contracts, forming long cracks and fissures. Ocean water seeps into these cracks to a depth of several kilometers, where it is heated by magma in Earth's mantle to as much as 350 degrees Celsius (660 degrees Fahrenheit). This superheated water then rises and eventually emerges from hydrothermal vents in the ocean floor as an underwater geyser. When the hot vent water meets cold ocean water, dissolved minerals in the vent water precipitate. In some places, compounds of iron and sulfides form "chimneys" on top of the vents.

Such an extreme environment seems unlikely to support life, given its high temperature, crushing pressure, and absence of light for photosynthesis. In 1977, however, Alvin, a manned submersible vessel built to withstand extreme pressure, dove to the deep ocean floor where its crew made a surprising discovery -- a vibrant ecosystem surrounding the hydrothermal vents of the mid-ocean ridges. Since that time, more than 300 new species have been identified at various vents around the world.

Bacteria called chemoautotrophs serve as the primary producers at the base of the hydrothermal vent food chain. These bacteria are functionally equivalent to plants, which serve as primary producers in terrestrial ecosystems by fixing carbon and creating sugars through the process of photosynthesis. In the absence of sunlight, these deep-sea bacteria must rely on another source of energy. As their name suggests, these chemoautotrophs break the chemical bonds of the mineral compounds found in abundance around hydrothermal vents and use this energy to fix the carbon necessary to sustain life. Other species in this unusual ecosystem, such as tube worms, clams, mussels, crabs, shrimp, and octopuses, use the energy captured by the bacteria to fuel their own activities.

The appearance of bacteria in these extremely hot, high-pressure, and dark environments has caused scientists to speculate that hydrothermal vents or places like them may have been sites of the earliest appearance of life on Earth -- fueled by water, energy from chemical reactions, and a rich supply of resources.

To learn more about how life might have originated on Earth, check out How Did Life Emerge Here?, Life Before Oxygen, and Caves: Extreme Conditions for Life.

To learn about some of the elements scientists think are essential to life, check out Ingredients for Life: Water, Life's Little Essential: Liquid Water, and Ingredients for Life: Carbon.

Classify symbiotic relationships between individual organisms of different species in this NOVA classroom activity.

Print Questions for Discussion

• What are deep-sea vents? How are they formed? Can you think of any equivalent structures or processes on land?
• What characteristics of the vent environment suggest life could have begun there?
• What is the ultimate food source in the vent community?
• What role do the organisms of deep-sea vents play in cycling certain elements?
• If similar geothermal conditions existed on other planets, do you think that life could form there? Explain.