projects. A good example is the Cenozoic climate curve of Zachos et al. (2001a), showing climate change over the last 70 million years using the proxy of 18O in marine microfossils.
One of the most significant, yet least understood, aspects of the deep-time climate record is the observation that Earth has moved between two major climate states—greenhouse and icehouse. Since the last transition between these two states occurred 34 million years ago at the end of the Eocene epoch, and the last time the Earth saw a transition from icehouse to greenhouse was nearly 300 million years ago, this is clearly a story told only by the deep-time record. This paleoclimate record contains facts that are startling to most people—there have been times when the poles were forested rather than being icebound; there were times when the polar seas were warm; there were times when tropical forests grew at midlatitudes; more of Earth history has been greenhouse than icehouse. Such relatively simple but relevant messages provide a straightforward mechanism for an improved understanding in the broader community of the importance of paleoclimate studies.
This message can be tailored to different audiences. For children, the simple comparison that dinosaurs lived in greenhouse conditions and mammoths lived in ice-house conditions can be an effective way to link a subject in which they are already interested to a phenomenon that should also interest them. With the first-order concept that the Earth’s climate alternates between these two major climate states, it is then possible to find ways to discuss and explain shorter-wavelength variations in climate, such as the orbital parameters that drove the glacial and interglacial shifts of the Pleistocene or the oceanic changes that drive the El Niño cycles. From the perspective of deep time, it is possible to start with the big patterns and work toward the small ones, and this is exactly what does not happen when the story starts from the perspective of daily weather.
The deep-time record also includes examples of extreme climate events and transitions. These examples are very useful as tools to help explain the range of possibilities in the Earth’s climate and to show how certain types of climate events can be abrupt, even when viewed from a human perspective. Examples such as the subdecadal warmings documented in the Greenland ice cores are useful to help people understand that just because something happened a long time ago, does not mean it took a long time to happen. With this realization, the deep-time record becomes a storehouse of useful and relevant examples. Ultimately, the goal of education and outreach from the deep-time perspective should be to help various audiences understand that the Earth has archived its climate