NCHHSTP Social Determinants of Health. Definitions. The National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention uses the words below to describe health equity and social determinants of health. These words are also used by the World Health Organization and the Department of Health and Human Service's Healthy People 2020.
Scientists have narrowed down several of the most likely causes of mass extinction. Flood basalt events (volcano eruptions), asteroid collisions, and sea level falls are the most likely causes of mass extinctions, though several other known events may also contribute. These include global warming, global cooling, methane eruptions and anoxic eventsâwhen the earth's oceans lose their oxygen.
Mass Extinction in the Fossil Record. Mass extinctions are apparent in the fossil record wherever some sort of organism virtually disappears from the geologic column above a certain layer. One of the most well-known mass extinctions is the disappearance of the dinosaurs and a number of other organisms at the K-T boundary.