Sentence:  A major adaptive radiation took place during the Cambrian Period that resulted in the evolution of most of the known phyla (broad groupings of organisms) as well as other phyla that have since become extinct. This geologically rapid appearance of diverse multicellular life is referred to as the <WSD>Cambrian explosion</WSD>, and is best documented in the fauna of the Burgess Shale (Middle Cambrian-age Stephan Formation) of British Columbia. 
Meaning of the word marked with <WSD> tags:  The relatively rapid appearance, during the Cambrian Period around 541 million years ago, of most major animal phyla, as demonstrated in the fossil record.