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Our Earth is about 70% covered in ocean, and the seafloor is a blanket of unconsolidated sediment made up of a wide range of organic matter, minerals, and chemistries. The habitable portions of ocean sediment provide living space for an estimated 3×10²⁹ microbial cells.

Scientists with the NASA Astrobiology Institute (NAI) Life Underground team based at the University of Southern California have used data on global sediment thickness, ocean depth, heat flow, and bottom water temperatures to developed a model to calculate the three-dimensional distribution of temperature in sediments.

The research, “Temperature and volume of global marine sediments,” is published in Geology. Seafloor temperature plays an important role, as it influences the thermodynamic tendency of reactions to happen, the kinetics of reactions, the diffusion of chemical species, and the physical properties of water that dictate the direction and speed of fluid flow.

The temperature model has revealed that more than 75% of the volume of Earth’s marine sediments is less than 80^oC, a range suitable for microbial activity in the subsurface. Temperature in about 25% of global sediment is less than 20°C, conditions most preferred by cold-loving psychrophiles. The results of the model in relation to microbial life is published in Microbe.

The research was supported by the Center for Dark Energy Biosphere Investigations, the NASA Astrobiology Institute, and the European Union Horizon 2020.