What change caused multicellular life to form?

The warming of Earth, accompanied by the seas covering the land, created the proper conditions for multicellular organisms to form.

Explanation:

There are many theories as to how multi-cellular life formed. The development of multi cellular life has occurred independently at least 46 times. It has been proposed that a minor genetic change in a molecule guanylate kinase protein-interaction domain (GKP-ID) may have allowed life to go from single to multi-cellular. It is also Possible a mutation of the DNA responsible for the mechanism of cell-division lead to the development of multi cellular life.

Explanation:

When the ice age ended and Earth warmed, the continents broke apart. This event allowed the shallow seas to cover the continents. The warming of Earth, accompanied by the seas covering the land, created the proper conditions for multicellular organisms to form.

A multicellular organism is an organism that consists of more than one cell, in contrast to a unicellular organism. All species of animals, land plants and most fungi are multicellular, as are many algae, whereas a few organisms are partially uni- and partially multicellular, like slime molds and social amoebae such as the genus Dictyostelium.