Extinctions have occurred numerous times over the history of the planet. More recent extinctions include Yangtze River dolphin, dodo bird, and Javan tiger. However, there have only been five mass extinctions in the history of the planet. A mass extinction occurs when a larger number of species of life on earth become extinct in a shorter period of time than normal. In a quick nutshell, the five mass extinctions in chronological order are the:
Ordovician-Silurian Extinction (444 million years ago) – about 100 marine families became extinct, including families of trilobites, conodonts, and graptolites.
Late Devonian Extinction (364 million years ago)– By now, both land and sea was habitable. This extinction seemed to only affect marine life, with 19% of all families and 50% of all genera becoming extinct.
Permian-Triassic Extinction (251 million years ago) – Considered Earth’s most severe extinction event, the Permian-Triassic Extinction resulted in the extinction of 90% of all marine species and 70% percent of terrestrial vertebrate species. Afterwards, fungal species became he dominant form of terrestrial life for quite some time.
Triassic-Jurassic Extinction (200 million years ago) – Half of all species on Earth at that time went extinct, leading the way for dinosaurs to become the dominant species in the Jurassic period.
Cretaceous-Tertiary Extinction (65.5 million years ago)- This is the famous mass extinction that led to the wipeout of the dinosaurs as well as 50% of all plant and animal species.
Today, 65.6 millions after the last mass extinction, experts are warning that the next one may be fast approaching. A report created by the International Program on the State of the Oceans (IPSO) presents grim prospects for the ocean, warning that if the level of damage currently done to the ocean continues, the world’s ocean will enter “a phase of extinction of marine species unprecedented in human history.” A combination of environmental factors and human interference has led to conditions that cannot continue to sustain the current amount of life in the ocean. There are three environmental factors – warming, acidification, and anoxia – that are particularly worrying. This “deadly trio” was present in some form or another in the past five mass extinctions and are heavily involved today’s potential ocean extinction.
The effects of global warming are putting enormous stress on many species in the ocean, especially coral. The slow but steady warming of the oceans waters have threatened the survival of coral reefs, with some scientists at the IPSO estimating that a quarter to a third of coral reefs have already died while another third have a high chance of dying out as well. Aside from serving as a natural shoreline buffer that protects against erosion and property damage, coral reefs are also the most diverse ecosystems on the planet, housing a wide variety of marine organisms that use the coral for food and shelter. The damage to the reefs will have severe repercussions on these species as well as the humans who have incorporated these animals into their life.
Acidification can occur when pH levels lower due to the oceans uptake of carbon. There have been previous instances of acidification in the Earth’s history, with levels increasing during periods of mass extinction. However, we are now at levels of acidification unheard of in history. To illustrate, during the Permian-Triassic mass extinction, carbon perturbations caused the uptake of 1-2 gigatons of CO2 per year in the oceans. In comparison, there are 30 gigatons of CO2 per year entering our oceans. The oceans do not have the capacity to neutralize this much CO2 quickly enough, thus lowering the pH of the water as well as the “saturation state”. Many calcifying organisms, such as coral reefs, require a certain saturation state to function. With the pH and saturation state of the oceans deteriorating, many organisms are finding it more and more difficult to survive.
The high levels of nutrients introduced by acidification and the increased temperature of the waters brought about by global warming creates ideal conditions for the growth of organisms such as bacteria and algae that require lots of oxygen. Their high oxygen use leads to the third member of the deadly trio- anoxia. Anoxic conditions in water occur when levels of dissolved oxygen are severely depleted. These areas are referred to as dead zones, because most marine organisms cannot function or survive without oxygen. If global warming and acidification continue, anoxic conditions will perpetuate leading to more and more dead zones in the ocean.
Scientists had long predicted that the oceans would face this kind of predicament, but it was not until the IPSO gathered and made their report that scientists realized that the ocean was in such bad condition. To prevent a mass extinction, not only must emissions be severely cut (Report co-author Professor Guldberg says world must move to zero emissions within the next 40 years), but fishing and dumping of chemicals must also eventually stop. Overfishing and chemical levels in the water are adding further stress to marine organisms who’s resilience levels are already falling due to the deadly trio. Unless something drastic is done, scientists at the IPSO fear that we may experience the sixth mass extinction.
Photo Credit: noaa.gov/features/resources_0908/images/whale_tail.jpg