If the values for both mass and volume double, the value of the density will be?

Stays the same.

Explanation:

Density = mass/volume

So if :

M/V = D

And if we were to double mass(M) and volume (V)

2M/2V = D

It will stay the same because the 2 and 2 would cancel out and we'd get the same density as the original value.

answer: land bridge theory. land bridge theory held that shifting portions of dry land explained the finding of identical species on different continents. plate tectonic theory eventually eliminated the land bridge theory.