 Good morning. I'm standing in a quarry in Lindenhall, Pennsylvania, and behind me is a series of limestones that were deposited in the ocean about 450 million years ago. This sequence of rocks provides us with a very valuable archive with which we can study Earth's climate back in the past. Each layer was deposited in sequence. This is the oldest layer here, and the youngest layers are up there. And what we can do is we can take samples of each individual layer and look at the fossils, look at the chemistry of the rocks, and tell a lot about what was happening to Earth's climate at the time that that layer was deposited, from the older layers down here to the younger layers at the top. There are many such sequences of rocks around the world that we can study to build ourselves a beautiful textbook of Earth's climate from the present day back to billions of years ago. And within these rocks there are little fossils that tell us about life at the times that these rocks were deposited. The chemistry of these rocks, things like isotopes and trace elements, will tell us about temperature, precipitation, salinity in the oceans, and then in some places there are plants. This plant is not within the rock, but in some cases the plants are preserved in the rock. And the fossils, leaves themselves, can tell us a lot about climate as well. So we can take marine rocks, we can take terrestrial rocks, we can tell us a lot about what was happening on land and in the oceans back in the past. And one other thing that we can look at are cores of ice. Ice cores are incredible archives of Earth's climate back through the past, and you can look at individual layers, black and white, in the ice cores, and that will tell us about what was happening in terms of precipitation and temperature on the ice when that ice was formed. So there's an amazing treasure trove of information about Earth's climate back through the past, and this is really important because we've just passed an important threshold in Earth's climate, just very recently. We passed a threshold of 400 parts per million CO2 in the atmosphere, and we have to go back millions of years to find times when these levels were as high. So these are the sorts of rocks that we can look at back in Earth's past to study the climate, to study life, and to study what was going on on our planet when CO2 levels were as high as they are today. So we're going to learn a lot about ancient climate in this module, and I hope you enjoy yourself. Thank you very much.