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.
There was at least 1 mass extinction event during this period that covered the time between 4.6 Ga (billion years ago) to 523 Ma (million years ago), occurring near the end of the period.During this period all organisms were soft-bodied, the first hard-shelled forms didn't evolve until the the Cambrian.here was at least 1 mass extinction event during this period that covered the time between 4.6 Ga (billion years ago) to 523 Ma (million years ago), occurring near the end of the period.