Leukonychia (or leuconychia), also known as white nails or milk spots, is a medical term for white discoloration appearing on nails. It is derived from the Greek words leuko (white) and onux (nail). The most common cause is injury to the base of the nail (the matrix) where the nail is formed.
Extinction Events. 1  There were many small-scale, sporadic extinction events during the Cambrian Period. 2  A large-scale mass extinction event occurred approximately 500 million years ago. 3  Scientists believe was caused by a significant decrease in global temperature. A large-scale mass extinction event occurred approximately 500 million years ago. 2  Scientists believe was caused by a significant decrease in global temperature. 3  Decrease in global temperature created an ice age-further eliminated many of the oceanic species.
By Laura Klappenbach. The Cambrian Period (543 to 505 million years ago) is the first time period of the Paleozoic Era. It is preceded by the Precambrian. The Cambrian Period opened in the aftermath of a mass extinction. During the last 100 million years of the Precambrian, a unique fauna had developed.arly in the Cambrian Period the first bivalves and arthropods appeared followed by the first mollusks, brachiopods, and trilobites. During the Cambrian Period, all but one of the major groups of animals evolved during a period of 40 million years.