How mountain ranges form

Many great mountain ranges were once sea floor. Sediment settles in a sea in flat, horizontal layers that harden into rock. When two plates push together, the layers between them are squeezed from the sides: they bend into folds, upfolds and downfolds like a pushed tablecloth, break along faults, thicken and are lifted high above the sea. That is why fossils of sea shells and corals are found near the tops of mountains. The Zagros formed this way: new sea floor in the Red Sea pushes the Arabian plate north-east into the Iran plate, which crumpled the old sea's layers into the long parallel folds you can see from a plane; the push goes on, so the Zagros still has many earthquakes. The Himalayas rose as India pushed into Asia.