At a depth of 3500 km, the Earth is in the liquid state, specifically within the outer core.

Here's why:

* Earth's Structure: The Earth is composed of several layers: crust, mantle, outer core, and inner core.

* Outer Core: The outer core lies between approximately 2,900 km and 5,100 km deep. It's primarily made up of iron and nickel, in a molten state due to extreme temperatures and pressures.

* Depth and State: At 3500 km, you'd be within the outer core, where the intense heat and pressure keep the iron and nickel in a liquid form.

While the outer core is liquid, the inner core, which lies deeper, is solid due to even greater pressure.