Answer:
Lithosphere
Explanation
As you know, the deeper you dig into the Earth, the hotter it gets. The lithosphere is the farthest from the core, therefore making it the coolest.
The lithosphere lies in the crust, and is the rigid layer.
Panama is an isthmus linking central and south america.
Answer:
The Economic Community Of West African States (ECOWAS) is a regional group of fifteen countries, founded in 1975.
Convection currents in the mantle still had not been discovered at the time.