From the 1995 lecture programme:
Water is an essential ingredient of the Earth, and without it we would not be here. Water reshapes our planet's surface through erosion and chemical weathering and, although we take it for granted, the position of the shoreline is one of the most changeable of all geological features.
Although it may not feel like it, we are living in an ice age now. At the moment we are in a warm period, and sea level is high, but just 20,000 years ago much of northern Europe was covered in ice and we could walk to France. Such fluctuations in climate have caused sea level to vary by as much as 120 metres over the last two million years.
One of the most astonishing recent discoveries is that the history of global sea level over this period is contained in the composition of tiny organisms preserved as fossils on the sea floor, and, furthermore, that the growth and decline of the ice sheets are related to the nature of the Earth' s orbit round the Sun. When we look at our neighbours, the Moon, Venus and Mars, we can imagine what the Earth would be like if we had no water, or if we lost it, or if the Earth's surface was not in the temperature range for water to be liquid. We are no longer restricted to the study of just our own planet. Space exploration has made us much more conscious of variations on our own theme: how small changes to the conditions on Earth can produce quite different geological environments, even though the processes that are operating are often recognisable. We are becoming much more aware of how special the Earth is