Which of the following are the main layers of the Earth?

The correct answer identifies the primary layers of the Earth as the crust, mantle, outer core, and inner core. This classification is essential in geology as it outlines the different physical and chemical characteristics present within the Earth's structure.

The crust is the outermost layer, consisting of solid rocks and minerals, and is where we live. Beneath the crust lies the mantle, which is semi-solid and plays a key role in tectonic activities and convection currents that affect the Earth's surface. The outer core is liquid and composed mainly of iron and nickel, whereas the inner core is solid due to the immense pressure that exists at the center of the Earth. Together, these four layers form the Earth's interior and help explain geological phenomena such as volcanic activity, earthquakes, and the formation of mountain ranges.

The other options include elements that do not categorize the Earth's layers accurately. The atmosphere relates to the layer of gases surrounding the Earth, while the hydrosphere pertains to water in all forms. The lithosphere is a term that often includes the crust and the upper mantle but does not accurately represent the depth structure of the Earth. The biosphere, on the other hand, refers to the global sum of all ecosystems and does not describe a physical layer of the Earth itself.