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.
Cambrian Explosion. âCambrian explosionâ refers to the great quantity and diversity of life found in what is called the Cambrian layer of the geologic column. The Cambrian age in the geologic time scale is dated by scientists as being about 530 million years old. What is really interesting is not just what is found in this layer, but what is found in the layers above it, and what is not found in layers under it. The Cambrian layer has virtually every phyla known to man.