Many thanks to Hiu Fan for this nice FDC from Hong Kong!Biodiversity is the degree of variation of life forms within a given ecosystem, biome, or on an entire planet. Biodiversity is one measure of the health of biological systems. Life on Earth today consists of many millions of distinct biological species. The year 2010 was declared the International Year of Biodiversity.Biodiversity is not consistent across the Earth. It is consistently rich in the tropics and in specific regions such as the Cape Floristic Province; it is less rich in polar regions where conditions support much less biomass.
Rapid environmental changes typically cause extinctions. 99.9 percent of species that have existed on Earth are now extinct. Since life began on Earth, five major mass extinctions have led to large and sudden drops in Earthly biodiversity. The Phanerozoic eon (the last 540 million years) marked a rapid growth in biodiversity in the Cambrian explosion—a period during which nearly every phylum of multicellular organisms first appeared. The next 400 million years was distinguished by periodic, massive biodiversity losses classified as mass extinction events. The most recent, the Cretaceous–Tertiary extinction event, occurred 65 million years ago, and has attracted more attention than all others because it killed the nonavian dinosaurs. The period since the emergence of humans has displayed an ongoing reduction in biodiversity. Named the Holocene extinction, the reduction is caused primarily by human impacts, particularly the destruction of plant and animal habitat. In addition, human practices have caused a loss of genetic diversity. Biodiversity's impact on human health is a major international issue.
Day of the bells in Prague - special Czech postmark - *Journée des cloches à Prague - TAD spécial tchèque * La veille de la saint-Sigismond (ou Zikmund), une journée des cloches ou des sonneries ("Den zvoníků"...
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