Why do lungfish walk on land?

The new findings support the theory that walking first arose underwater, preceding the move onto land and the development of toes and limbs adapted to land perambulation.

answer is: naturally occurring solid, inorganic compound or element is mineral.

minerals usually have crystalline form, that means than crystal constituents (atoms, molecules or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions.

for example magnetite is a mineral of iron oxide (fe₂o₃).

calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (caco₃).

dolomite is an   carbonate mineral composed of calcium magnesium carbonate (camg(co₃)₂).

gasoline is a mixture. it contains several different kinds of compounds that can be present in a variety of ratios.