The planets formed out of a cloud of gas and dust around the nascent Sun. Within the so-called snow line, it was too hot for liquid water to exist. Since the Earth lies well within this line, why does it have water? Did it somehow manage to retain water from the outset or did it acquire its water later? In the podcast, Lindy Elkins-Tanton explains how these two scenarios might have played out but she says the evidence strongly favors one of these theories.

Elkins-Tanton has concentrated much of her research career on the formation and evolution of planets, and especially the role of water. She is a Professor in the School of Earth and Space Exploration at Arizona State University and Principal Investigator of the NASA Psyche mission.

Golden spikes are not golden, nor are they generally spikes. So what are they, and, more importantly, what exactly do they represent? In the podcast, Joeri Witteveen explains how we arrived at our present system of defining the boundaries of stages in the rock record with a single marker. Paradoxically, it turns out that the best place for a golden spike is where “nothing happens.” Listen and find out why.

Witteveen is Associate Professor of History and Philosophy of Science at the University of Copenhagen.

The late Paleozoic ice age began in the Late Devonian and ended in the Late Permian, occurring from 360 to 255 million years ago. It was similar to the present day in two key respects: rising atmospheric CO2 and recurrent major ice sheets. In the podcast, Isabel Montañez explains how we can use proxies to learn about the climate and ocean conditions that prevailed then. And with the help of a model, she says that we can also learn about sensitivities and feedbacks of Earth systems to rising CO2. Among other things, the model suggests that when the atmosphere reaches the present day level of CO2, significant parts of the ocean may become anoxic and ocean circulation patterns alter.

Montañez is a Distinguished Professor in the Department of Earth and Planetary Sciences at the University of California, Davis.