Mass Extinctions

NUMBER OF GENERA was marineat thetime,86% oflife was lost. unable to survive theincreased temperature. Sincemostfauna again. Creatures that hadadapted to thecoolerclimate were reducing Later habitat. cameglobalwarming level andsea rising cooling andglacierformation. Thisledto adrop levels, insea life removed carbondioxide (CO extinction: aglaciation event andaheating event. Abundantplant Scientists theorize that there were two to mainphases this 440 1. ORDOVICIAN-SILURIAN EXTINCTION MASS EXTINCTIONS MASS 1000 2000 3000 4000 MILLION YEARSAGO (MA) Cambrian 500 of oxygen (O algae bloomsconsumedvast amounts oceans that fed ofthis, algae.Because an abundanceofnutrientsinto the plants developed deeproots, releasing period. Onetheorysuggeststhat land About 75% oflife diedoffduringthis EXTINCTION—365 MA 2. level, leadingto habitat loss. resulting inglaciation andafall insea that anotherglobalcoolingtook place, many Anothertheorysuggests species. LATE DEVONIAN Ordovician 2 ) from theair, causingglobal 2 ) in the oceans, suffocating) intheoceans, Silurian 400

Devonian

86% 86% 75% 75% LOSS LOSS GEOLOGIC TIMEIN MILLIONS OFYEARS CO the atmosphere. Bacteria that thrive on carbon dioxide, agreenhouse into gas, activity inSiberiaputmassive amountsof perished. Scientistbelieve that volcanic extinction inhistory: 96% ofalllife The Permian-Triassic was thedeadliest EXTINCTION—252 MA 3. toxic environment for life. rain creating acidic, ahighly with Earth’s water, makingtheoceanand warmedgases theplanetand combined greenhouse Large gas. quantitiesofboth 2 PERMIAN-TRIASSIC beganproducing methane,another Carboniferous the dinosaur’s ancestors. makingwaymost ofthemammals, for life was lostinthisextinction, including triggered theextinction. About80% of that anasteroid orcometimpact extinction. contend scientists Other causingthismass acidified theoceans, atmosphere, whichtrapped heat and eruptions spewed tons ofCO theorizeSome scientists that volcanic EXTINCTION—201.3 MA 4. TRIASSIC-JURASSIC than 75 percent ofanimalspecies. identify five massextinctions inEarth's history, eachofwhichledto alossofmore catastrophic event orrapid environmental change.Scientistshave beenableto A massextinction isasharpspike intherate ofextinction by ofspeciescaused a 300

Permian

96% 2 LOSS into the

Triassic

impact may have localfires, caused also earthquakes, andacidrain. tsunamis, amounts ofdebrisinto theatmosphere, causingglobaltemperatures to drop. The Peninsula inMexico andkilledthedinosaurs. Theimpactwould have ejected enormous of alllife onEarth. Awidelyaccepted theory is that anasteroid landedintheYucatán The Cretaceous-Paleogene extinction wipedoutthedinosaurs, alongwith60–76% 5. CRETACEOUS-PALEOGENE MA EXTINCTION—66

80% LOSS 200 Jurassic environment ofextinctions istheleadingcause today. record. Scientistsbelieve that humanimpactonthe time withouthumaninfluence,determined by thefossil extinction onthelongevity based ofspeciesthrough or background extinction rate istheaverage rate of greater thanthe“normal” extinction rate. A“normal” The current extinction rate isat least athousandtimes The next massextinction may already behappening. 11,700 YEARSAGO TO PRESENT 6. HOLOCENE EXTINCTION Cretaceous 100 Cenozoic

0 (PRESENT)

60-76% 60-76% LOSS LOSS