Early History of Titan
Recall the early history of the terrestrial planets: significant heating from heavy bombardments. The internal structure of Titan at the close of the accretion phase, about 3.5-4 billion years ago is shown to the right. Energy sources in the early ocean include kinetic energy from meteorites and comets. During this time, the ocean was exposed at the surface creating a warm (»300K) aqueous environment with abundant energy sources. This is the closest Titan is ever likely to have come to the primitive terrestrial environment in which life is thought to have formed on Earth.

Titanian microbes, in the absence of free oxygen are likely to have developed as anaerobes. Given also the low sunlight levels at Saturn's distance from the Sun potential micro-organisms are unlikely to have been dependent on sunlight for energy. They would likely have been chemosynthetic autrotrophs as the ocean was soon roofed over by a layer of ice. and the crust acquiring a thickness of ~30km after approximately 70 million years.

What about Sub-Surface liquid water?
It has been shown that if an ocean was present following accretion then an ocean is almost certainly present today, deep beneath the icey crust. Based on heatflow estimates and the viscosity of the ice crust, scientists estimate there to be a contemporary ocean of liquid water and ammonia with a depth of about 200 km.

Tests for the presence of a subsurface ocean
A liquid layer in Titan's interior reduces the overall rigidity of the moon. The Cassini mission to Saturn will yield, in the course of numerous flybys, a sensitive measure of the gravitational rigidity of Titan. Also, a complex magnetic field signature, induced by a conductive liquid shell, might also be used to infer a liquid layer.