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.
During the PermianâTriassic mass extinction event 252 million years ago, most life on Earth perished. Scientists have now obtained evidence that ocean acidification played a key role in the die-off. The new research was published in the journal Science on April 10, 2015. The PermianâTriassic mass extinction event is the largest such event to ever to have occurred on Earth. About 90% of all marine species and 70% of all terrestrial species died off during this time. It was much worse than the mass extinction event that killed off the dinosaurs 65 million years ago.