I'm in the Hall Planet Earth, and I'm standing in front of a series of marble cylinders that illustrate how rocks deform. This is Carrera marble, the same white marble that Michelangelo used to create David, and it's still being mined in Italy. And all of these cylinders. started out just like this one, to which nothing has happened. But in these other cylinders, we compressed them at, under different conditions to illustrate how rocks deform. An important property of rocks is that they their, their deformation is different. The manner in which they deform. is different, depending on the conditions of deformation. In our everyday experience, we realize that rocks can break, they behave brittlely, but there are other conditions in which rocks actually flow, like putty, like plastic, and that transition from brittle. To what's known as ductile deformation are illustrated by these cylinders. So, all of these cylinders began life like this cylinder on the left and nothing has happened to this. But all of these other cylinders. Were deformed under a compressive stress at 400 degrees centigrade, so in other words, very high temperature, and at progressively higher confining pressures. These particular cylinders you can clearly see fractured, and in fact, so did these two, but the fractures in these two cylinders are much smaller and they're more difficult to see. In contrast, these cylinders did not fracture yet you can see they're both shorter. These cylinders experience what's known as ductile deformation. The deformation is accomplished by the change in the shapes of the grains that actually make up these cylinders. So this is a microscopic process. This is a macroscopic. Process. This illustrates the very important property again that rocks flow. That's a very, very important property because it really determines the nature of the planet for example. The mantle of the Earth is largely solid, but it flows. It's the reason that we have plate tectonics. So it's a consequence of the fact that rocks can behave ductily under conditions of high temperature and pressure.