The part of Earth's layers that is about 2300 km thick is the mantle.

Here's a breakdown of the Earth's major layers and their approximate thicknesses:

* Crust: 5-70 km thick (varies greatly depending on location)

* Mantle: 2890 km thick (this includes the upper and lower mantle)

* Outer Core: 2200 km thick (liquid iron and nickel)

* Inner Core: 1220 km thick (solid iron and nickel)

Let me know if you'd like more information about any of these layers!