The+Cambrian+Explosion

Many of the major phyla of animals arose during the Cambrian period, in what is called the Cambrian Explosion. Prior to the Cambrian period, simple one-celled organism had slowly evolved into primitive multi-cellular creature. Then, in a relatively rapid explosion during the period from 540 million years ago to 500 million years ago, there was a period of astonishing <range type="comment" id="564672705_9">diversification </range id="564672705_9">in which quickly developing organisms became <range type="comment" id="564672705_10">widely </range id="564672705_10"><range type="comment" id="564672705_11">distributed</range id="564672705_11"> and formed complex <range type="comment" id="564672705_12">communities</range id="564672705_12">. One theoretical explanation for the rapid diversification that occurred during the Cambrian period is known as the theory of polar <range type="comment" id="564672705_13">wander</range id="564672705_13">. According to this theory, the rapid diversification <range type="comment" id="564672705_14">occurred </range id="564672705_14">because of an unusually rapid reorganization of the Earth's <range type="comment" id="564672705_15">crust </range id="564672705_15">during the Cambrian period. This rapid change in the Earth's crust <range type="comment" id="564672705_16">initiated </range id="564672705_16">evolutionary change <range type="comment" id="564672705_17">inasmuch </range id="564672705_17">as change in the <range type="comment" id="564672705_18">environment </range id="564672705_18">serves to <range type="comment" id="564672705_19">trigger </range id="564672705_19">evolutionary change.