The part of the Earth that is about 1802 miles thick is the Earth's mantle.

Here's why:

* Earth's Crust: The Earth's crust is the outermost layer and is only about 3-45 miles thick.

* Earth's Mantle: The mantle lies beneath the crust and extends down to about 1800 miles.

* Earth's Core: The core is the Earth's innermost layer, divided into a liquid outer core and a solid inner core.

While the exact thickness of the mantle varies slightly, it's generally considered to be around 1800 miles.