I work on a wide variety of projects that all have a thread in them of working out how the planet has operated over the 4.6 billion years of its history.
Much of the research I get involved in with PhD students is about mapping the ancient plate tectonics of the planet. Where were continents in the past? Where were the subduction zones, the mid ocean ridges?
This is not a straightforward question in the really ancient Earth because we have lost all the oceanic crust older than about 200 million years old. Before that, we need to use more subtle proxies for the existence of now long defunct plate margins.