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 Cambrian spans from 540 million years to 485 million years ago and is the first period of the Paleozoic and of the Phanerozoic eon. The Cambrian sparks a boom in evolution in an event known as the Cambrian Explosion in which the largest number of creatures evolve in the history of Earth during one period.he Cambrian spans from 540 million years to 485 million years ago and is the first period of the Paleozoic and of the Phanerozoic eon. The Cambrian sparks a boom in evolution in an event known as the Cambrian Explosion in which the largest number of creatures evolve in the history of Earth during one period.