The third theme of deep biosphere research is the Limits of Life: Extremes and Norms of Carbon, Energy, Nutrient, Temperature, Pressure, and pH. There are many different ways that animal and plant life are tested to their limits. The marine realm has long been fertile ground for research into the extremes at which life can thrive and survive. A classic example was the 1977 discovery of life at hydrothermal vents where organisms were found to be thriving in water well above the conventional boiling point. That discovery changed our understanding of the limits of life, especially with regard to temperature.