Extinction

What do dinosaurs, Tasmanian Tigers and Hoopoe Starlings have in common? The answer is the subject of today's lab, extinction. Extinction occurs when a species cannot survive in its environment to reproduce and cannot move to a new one. Woolly mammoths, for example, were thought to have died as a result of climate change making its habitat and the rest of the planet too warm. Extinction has happened for as long as there has been life on earth. In fact, an estimated 99% of all species that ever existed have gone extinct.

Most of these extinctions happened over time because of environmental changes like our woolly mammoth. But other factors such as competition for resources with other species and inability to avoid predation can also drive a species to extinction. Take these fish, for example. Both species share a habitat, but the green fish is better at evading predators making its survival more likely and eventually driving the orange fish extinct. Over hunting and other human made phenomena such as pollution can also cause the extinction of a species.

Extinctions that occur on a global level are called mass extinctions and these are typically caused by major catastrophic events like impacts from space, significant volcanic activity and other phenomena that cause global climate change. During these events, high rates of extinction exceed the rates of new speciation resulting in a global loss of species.

The best known mass extinction is the Cretaceous-Paleogene or K-Pg extinction, famous for ending the reign of the dinosaurs. This extinction can even be seen in the rock layers or strata of the earth where we see an abrupt loss of species from the fossil record around 66 million years ago, which also coincides with a unique sediment layer containing iridium a metal not often found in the earth's crust. Iridium is, however, present in high amounts in asteroids, giving scientists a clue to the cause of the extinction. The impact at the Yucatan Peninsula in Mexico created the 180 kilometer wide Chicxulub Crater and triggered a string of catastrophic events that would alter the earth forever. First, fire storms would have ravaged the North American continent creating a huge cloud of smoke and dust. Debris ejected from the collision would have become trapped in the upper atmosphere causing a blanketing effect, which trapped deadly amounts of infrared radiation in the atmosphere. Volcanic eruptions and widespread geological instability following the impact fueled the smothering of the earth yet further and as the soot, smoke and volcanic ash blocked the sun, many plants were no longer able to photosynthesize and so perished. Without food, the herbivores were the next to die out, followed closely by the predators. The volcanic emissions and resulting smog caused acid rain which acidified the oceans wiping out many aquatic species. Soon, the acidic atmosphere and dense fog blocking the sun's warmth led to a deep freeze with global temperatures dropping below zero for several years. The mass extinction caused by these drastic environmental changes affected every known and three quarters of all species alive at the time went extinct in the evolutionary equivalent of the blink of an eye.

Over time, as the earth's climate slowly returned to normal, the remaining species which included small mammals rebounded and underwent adaptive radiation to fill the many newly vacated In this way, the loss of a great number of species during the mass extinction opened up room for the expansion and speciation of others.
In this lab, you will examine diversity data for several distinct taxa at different time periods around the Cretaceous-Paleogene extinction.