A lot of work was being done at that time on self-organising systems. Ilya Prirogine had been studying systems far from thermal or chemical equilibrium which nevertheless showed a high degree of order, for example the Belousov-Zhabotinskii reaction which produces amazing periodic oscillations. He realised that there was a close association between self-organisation at states far from equilibrium, and the nonlinearity of the system. This tied in well with Lovelock's observation that the Earth is chemically far from equilibrium, and the nonlinearity of the feedback loops such as the carbon dioxide cycle. What is important in this definition is not so much the material structure of life as the process, organisation and set of relations between the components.
Life is a network which constantly makes itself.
The simplest autopoietic system is the living cell. While the Gaia Hypothesis attracted a lot of interest, it also received a great deal of criticism. Lovelock had attached great weight to the idea that the Earth seemed to regulate itself. Some took this to imply that the Earth was behaving with a sense of purpose, that it was a teleological being. It is part of a very old debate between mechanists who believe that nature essentially behaves like a machine, and vitalists who believe there is a non-causal life force.