1. a. Lithosphere
If we divide the Earth into layers by their composition, then there are three of them, the crust, mantle, and core. The crust is the thinnest layer, being on the top, and being solid. The mantle is the second layer, lying between the crust and the core. It is a layer where the temperature and pressure are higher, and the rocks are hot and slow-moving. The core is the bottom layer, in the center of the planet. It is the hottest and has the highest pressure, being the densest of the layers and is composed mostly of iron and in lesser percentage of nickel.
2. b. Crust
The Earth is divided into several layers depending on the layers being solid or liquid. There are five different physical layers, lithosphere, asthenosphere, mesosphere, outer core and inner core. The lithosphere and the inner core are the two layers that are solid, thus the layer on top and the layer in the center. The asthenosphere, mesosphere, and outer core are all liquid, though it is a different degree of liquidity, and it is these three layers where the convection currents occur and cause the magnetic field of the Earth, as well as the tectonic movements.
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The biggest and probably the most important engineering feat the Romans achieved was the construction of aqueducts. These aqueducts were used for two crucial purposes among others, water supply and water flow out.
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