Environment
The Ordovician-Silurian extinction occurred about 439 million years ago due to a drop in sea levels as glaciers formed followed by rising sea levels as glaciers melted.
The Late Devonian extinction took place somewhere around 364 million years ago. To this day its cause is unknown.
The Permian-Triassic extinction happened about 251 million years ago and was Earths worst mass extinction. 95 percent of all species, 53 percent of marine families, 84 percent of marine genera, and an estimated 70 percent of land species such as plants, insects and vertebrate animals were killed during this catastrophe. Direct evidence for this period has not been found but many scientists believe a comet or asteroid impact lead to this extinction.
The End Triassic extinction, taking place roughly 199 million to 214 million years ago, was most likely caused by massive floods of lava erupting from the central Atlantic magmatic province triggering the breakup of Pangaea and the opening of the Atlantic Ocean. The volcanism may have led to deadly global warming. Rocks from the eruptions now are found in the eastern United States, eastern Brazil, North Africa and Spain. 22 percent of marine families, 52 percent of marine genera, and an unknown percentage of vertebrate deaths were the result.
The Cretaceous-Tertiary extinction occurred about 65 million years ago and is thought to have been aggravated, if not caused, by impacts of several-mile-wide asteroid that created the Chicxulub crater now hidden on the Yucatan Peninsula
The Sixth Mass Extinction has begun!
As unbelievable as it may sound, after having read through the five mass extinctions, the sixth mass extinction is in progress, now, with animals going extinct 100 to 1,000 times (possibly even 1,000 to 10,000 times) faster than at the normal background extinction rate, which is about 10 to 25 species per year. Many researchers claim that we are in the middle of a mass extinction event faster than the Cretaceous-Tertiary extinction which wiped out the dinosaurs.
Rather than a meteorite or large volcanic eruption, the alarming decline of biodiversity (diversity of species on earth) leading to the current mass extinction is the results of five major human activities:
- Habitat destruction including human-induced climate change. Human-induced climate change is the result in high amounts of greenhouse gas emissions (primarily carbon dioxide, methane, and nitrous oxide). Acting like a greenhouse, these gases trap heat from the sun. Other human activities such as habitat destruction in combination with climate change are making the situation only worse. Increasing temperatures may force species to move toward their preferred, and generally cooler, climate range. Thus, if those habitats have already been destroyed, then the species are not be able to escape the climate change and will go extinct.
- Invasive species. Invasive/aliens species displace native species through predation, competition, and disease organisms.
- Pollution.
- Human overpopulation.
- Over-harvesting (hunting, fishing, and gathering).
The Hawai'I chaff flower, the golden coqui Puerto Rican tree frog, the Martinique Parrot, the Yuman box turtle, the Madagascan Pygmy hippo, and the Japanese sea lion are amongst the list that include the 784 species of plants and animals that have recently vanished from earth because of human activities. All continents are impacted by this ongoing biological catastrophe. The completion of species inventory on earth and saving them from becoming extinct must be a world priority.
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