Six mass extinctions: causes and consequences

Abstract

Masovna izumiranja relativno su kratki periodi geološkog vremena kada je izumro veliki dio vrsta na Zemlji. Karakteriziraju ih velika stopa i magnituda izumiranja te vrlo dug period oporavka. Istaknuto je pet masovnih izumiranja i nekoliko manjih izumiranja u geološkoj prošlosti Zemlje. Mnogim istraživanjima definirani su primarni uzroci pokretači tih izumiranja, poput vulkanizma, ali posljedični čimbenici poput anoksije i klimatskih promjena te njihov udio u izumiranju su diskutabilni. Zbog naglih promjena u oceanima, gdje većinom vladaju konstantni uvjeti, sva su masovna izumiranja imala najveći utjecaj na morske organizme. Dominantne i široko rasprostranjene skupine poput amonita, trilobita i dinosaura zauvijek su izbrisane s lica Zemlje, a drugim su organizmima otvorene nove ekološke niše i evolucijski putevi. Mnogi znanstvenici upozoravaju da je zbog velike moderne stope izumiranja šesto masovno izumiranje već započelo. Potrebna su mnoga istraživanja i mjere zaštite kako bi se te stope smanjile i osigurao daljnji tijek života na Zemlji, kakvog ga poznajemo.Mass extinctions are relatively short periods in geological time during which majority of species on Earth went extinct. They are characterised by a large magnitude and extinction rate and a very long period of recovery. Five mass extinctions and a few minor extinctions that occurred during the Earth's geological history are being defined. Main causes of these extinctions, such as volcanism are well known, but consequential factors like anoxia and climatic changes and their share in extinctions are questionable. Due to sudden changes in oceans, where life conditions are mostly constant, marine life was most severely affected by mass extinctions. Dominant and widespread groups of organisms like ammonites, trilobites and dinosaurs went extinct, thereby opening new ecological niches and giving a chance for evolution of other organisms. Many scientists warn us that because of great modern extinction rates, the sixth mass extinction has already begun. Many more researches and protection measures are required for reducing these rates and for securing the future of life on Earth as we know it