200 km down from the Earth's surface would be within the Earth's mantle.

Here's why:

* Earth's Crust: The Earth's crust is the outermost layer and ranges from about 5 km (oceanic crust) to 70 km (continental crust) thick.

* Earth's Mantle: The mantle lies beneath the crust and extends down to about 2900 km. This layer is mostly solid rock, but it behaves like a very viscous fluid over long periods.

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

Since 200 km is well past the typical thickness of the crust, it would be firmly within the mantle.