There are only two chemical elements which are significantly magnetic and reasonably common and had appropriate densities, andThey concluded therefore that the Earth had to have amade of
and

Pls help me out

Iron and Nickel

core

Iron and Nickel

Explanation:

Two of the most popular magnetic chemicals in the world are iron and nickel.

We can now match these metals with the description given in the question to check if they perfectly fit in the blanks.

The densities of iron and nickel are 7874kg/m3 and 8900kg/m3 respectively. To put this into perspective, the density of aluminium is only 2700kg/m3. This means that iron and nickel are really dense solid materials.  These materials are strong enough to make the core of the earth.

Because these materials are also magnetic and strong, we can say that they are the materials that form the solid core of the earth's structure.

answer; they use longitude and latitude and   global grid system; good luck

answerthey are called the pampas;