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.
The authors of this latest study therefore argue that the increase in atmospheric oxygen during the Cambrian canât have been what caused the sudden explosion of life. They instead suggest that it resulted from a revolutionary change within the animalsâ own biology, rather than being driven by environmental factors.