What is the layer of Earth that comprises 70% of its volume?

The layer of Earth that comprises 70% of its volume is the Earth's mantle. This thick layer lies between the Earth's crust and its outer core. The mantle is primarily composed of silicate minerals that are rich in iron and magnesium, and it plays a critical role in geological processes such as plate tectonics and volcanic activity.

The mantle's significant volume is due in part to its extensive thickness; it extends about 2,900 kilometers (approximately 1,800 miles) down to the outer core. The properties of the mantle change with depth, where temperatures increase and materials can behave as both solid and semi-fluid, allowing for convection currents that drive much of the dynamic activity of the Earth's surface.

In contrast, the Earth's crust is much thinner and accounts for only a small percentage of the total volume. The outer core, primarily made of liquid iron and nickel, and the inner core, which is solid and composed of iron and nickel, also make up smaller portions of the Earth’s overall composition. Thus, the mantle's dominant volume is a key aspect of the Earth's structure and function.