Brittle Vs. Ductile: Big Hunk as a Model for Earth's Crust & Mantle

So you take a big hunk of candy bar, you stick it in the freezer overnight. And keep it cold until you're going to use it. And then you can attempt to bend it. And you can show that even a slight little bend to the big hump candy bar when it's cold, will cause it to fracture. You really can't bend it hardly at all. It's very brittle. So it's very easy to fracture. Same material now, a warm big hug candy bar. And in class, I do the trick of keeping candy bar inside my shirt. Pull it out. So when the candy bar that's been on bomb's belly here for a while, up to that point in the lecture, is warm. And it's modeling the mantle material down and the esteemed sphere. 

The deeper, hotter part of earth's mantle. The warm big hump candy bar, if you're gentle with it, you can bend it. Without breaking them. In fact, if it's warm enough, if it's been on bomb's belly long enough, and it's warm enough, you can bend it right over. And you can make an omega on that thing. You can make the ends of a touch. So it's very difficult. Now, consider this is a really small difference in temperature. Cold, big hunk, candy bark, it's been in the freezer of your fridge overnight is round about 0°C. Warm, big hung candy bar if it's been on your belly is about 90°F, that's about 30°C. So that's only 30°C, temperature difference between the very cold, brittle, become candy bar and the warm ductal big hub candy bar. 

Small difference in temperature, huge difference in the mechanical properties. And so that helps people to get the idea that we take mantle material here, mantle makes up the majority of the oceanic lithosphere plate here. We call this lithospheric mantle here. It's cold enough to be brittle and fractured and give us earthquakes. Underlying status mantle, too warm, not liquid, but this going elastic it will flow its plastic-like material when you deform it over long time scales. So it's the warm