The “big five” are not the only extinctions in the history of life on earth, but they have been the most devastating. Fossils of marine animals indicate that each event wiped out at least 17 percent of families – mind you, one family could have dozens, even thousands of species. Scientists are still puzzling over what caused the big five – climate change, perhaps caused by cosmic impacts - is a leading suspect. Mass extinctions can last for millennia, and it takes millions of years for new species to make up the loss. Here is some more information on the “big five”:

1. Ordovician: 440 million years ago, 25% of families lost. Life had begun in the sea more than three billion years ago. Trilobites suffered, but survived.

2. Devonian: 370 million years ago. 19% of families lost. Life had come to land, but the sea lost many forms of fish and reef-building invertibrates.

3. Permian: 250 million years ago, 54% of families lost. In the most catastrophic loss of life, trilobites became extinct, as did many insects.

4. Triassic: 210 million years ago, 23 % of families were lost. This extinction claimed mammal like reptiles and many invertebrates. Dinosaurs and early mammals then flourished.

5. Cretaceous: 65 million years ago, 17% of families were lost. Mammals survived this extinction, but didosaurs did not.

And now we stand witness to the earth’s sixth mass extinction – called the Quarternary: Scientists. Experts agree that humankind has ignited this one, unlike in the past, and is driving it fast. Among the hardest hit so far are beetles, amphibians, birds, and large mammals. However, recent research suggests that some 50% of the world’s flora and fauna could be on the path to extinction within 100 years. Everything will be affected – fish, birds, insects, plants and mammals. 1,100 of the world’s nearly 10,000 species of birds - eleven percent – are on the edge of extinction and it is doubtful that majority of these will live beyond the end of the 21st century.