And at least in my country people are excited about the possibility that Mars is one of these objects (fig.51), maybe not always for the best reasons. But it has excited the Press, and a number of the scientists , to ask the questions： How would we know whether life ever began on Mars? How do we test this idea? And even a more exotic object, Jupiter's moon Europa (fig.52), which seems to have an ice or ice and water layer a hundred kilometers thick that is being tidally flexed to such a degree that the ice is probably continually being heated, if not melted, to a substantial depth. So this might be another object with an ocean, although not a surface ocean. So the question is could life have begun there ? NASA is exploring this question with a series of spacecraft missions.
So Earth is indeed a living planet (fig.53), and it's living in the sense of all of us living. It's living in the sense of the incredibly dynamic atmosphere and oceans and sub-surface on which we live.
I don't know if you detected this, but through all of the processes that I've talked about - the coupled systems and the examples of research frontiers - a key thread through all these discussions is water - liquid water. Water is critical for driving the climate system, through ocean-atmosphere interactions, through evaporation and transpiration. It's a major controller of our weather. Water is critical to the plate tectonic cycle, for cooling the sea floor, for contributing to the volcanism at places like Japan. Water may in fact be critical for enabling plate tectonics. There's been some new work on mantle convection that suggests that the only way a planet (and the Earth is the only planet that shows plate tectonics) can have a convection system that involves plate tectonics is if there are very weak faults. What makes them weak? Maybe it's water, again - water carried down into the subduction zone. Water, of course, is an essential ingredient for life. Water makes up most of our bodies. So all of the topics we've been talking about hinge on water. And water - the oceans - is also the scientific frontier for Earth Science for the whole of the 21st century.
So I think it is very fitting that we are all here today to talk about OD21 as one of the very important tools in exploring that research frontier, technology that will allow us to advance our knowledge across many questions and improve our understanding of our wonderful, living planet. Thank you
