पर्यावरण :क्या तकरीबन पचीस करोड़ बरस पहले पृथ्वी पर से ९० फीसद जीवों के सफाये की वजह एक माइक्रोब बना था जो ग्रीन हाउस गैस छोड़ता था ?

Climate-changing microbes 'made 90% of species on earth 

extinct'

सुदूर अतीत में पृथ्वी पर जीवन का बड़े पैमाने पर कई मरतबा सफाया हो चुका है कभी कयास लगाया गया के इस सफाये की एक बार अब से कोई साढ़े छः करोड़ बरस पहले धूमकेतु वजह बने थे जब डायनासोरों का बड़े पैमाने पर सफाया हो गया था। 

कई और बार  ऐसे सफाये की वजह ज्वालामुखी विस्फोटों को भी बतलाया गया है। अब साइंसदानों के मुताबिक़ अब तक के ऐसे एक सबसे बड़े सफाये की वजह चंद माइक्रोब्स (सूक्ष्म जीवाणुओं )को बतलाया जा  रहा है। 

समझा जाता है अब से कोई पचीस करोड़ बीस लाख बरस पहले सूक्ष्म जीवाणु मिथेनोसरसीना (methanosarcina )का उस समय समुन्दर में सैलाब सा आगया था। क्योंकि यह जीवाणु मीथेन छोड़ता था अत: :समुन्दरों का जल यकदम से तेज़ाबी (अम्लीय ) हो गया था। तापमानॊ में इस ग्रीनहाउस गैस से यक -बा -यक बे -शुमार बढ़ोतरी हुई जिससे जीवों का बड़े पैमाने पर सफाया हुआ। 

इस सफाये (Permian mass extinction )के कोई दो करोड़ बरस बाद पृथ्वी पर भीमकाय प्राणी डायनासोर प्रगट हुए। 

ज़ाहिर है हमारा कुदरती पर्यावरण हमारी हवा हमारा पानी हमारी मिट्टी सूक्ष्म जीवाणुओं के उद्भव के  प्रति बहुत संवेदी है। जलवायु परिवर्तन का कारण भी बने हैं ऐसे जीवाणु। आइंदा भी ऐसा हो सकता है। 

तेल कुओं ,कचरा दफ़न की जगहों जुगाली करने वाले जीवों की अंतड़ियों में  आज भी ऐसे ही मीथेन निसृत करने वाले जीवाणु मौज़ूद है। तरह तरह के कचरे का प्रबंधन और निपटान एक महती समस्या रहा आया है। सागरों में चोरी छिपे कचरा लिए जहाज घूमते रहते हैं। 

आदमी का बढ़ता कार्बन फुटप्रिंट एक मरतबा हमें  फिर ऐसे ही विनाश की और ले जा सकता है। जीवाश्म ईंधनों के विकल्प हमें  तलाशने ही होंगें वरना आज या कल ऐसा ही एक और विनाश टाला न जा सकेगा। 

पढ़िए इसी आशय की यह रपट : 

A fossil of a trilobite, a horsecrab-like creature that thrived in the seas for hundreds of millions of years before becoming one of many kinds of animals wiped out in a mass extinction that befell the planet 252 million years ago. Photo: Reuters

Climate-changing microbes may have caused the biggest mass extinction in history 252 million years ago, scientists believe.

Volcanic eruptions had previously been blamed for the sudden loss of 90 per cent of all species on earth at the end of the Permian era.

But new research suggests volcanoes played only a bit part in the catastrophe.

The chief perpetrators were a microscopic methane-producing archaea life-form called methanosarcina that bloomed explosively in the oceans.

Enormous quantities of methane, a potent greenhouse gas, generated by methanosarcina are thought to have sent temperatures soaring and acidified the seas.

Unable to adapt in time, countless species died out and vanished from the earth.

The horseshoe crab-like trilobites and the sea scorpions - denizens of the seas for hundreds of millions of years - simply vanished. Other marine groups barely avoided oblivion, including common creatures called ammonites with tentacles and a shell.

On land, most of the dominant mammal-like reptiles died, with the exception of a handful of lineages including the ones that were the ancestors of modern mammals, including people.

"Land vertebrates took as long as 30 million years to reach the same levels of biodiversity as before the extinction, and afterwards life in the oceans and on land was radically changed, dominated by very different groups of animals," said US scientist Gregory Fournier, from the Massachusetts Institute of Technology (MIT).

The first dinosaurs appeared 20 million years after the Permian mass extinction.

"One important point is that the natural environment is sensitive to the evolution of microbial life," said Daniel Rothman, an MIT geophysics< professor who led the study published in the journal Proceedings of the National Academy of Sciences.

The best example of that, Professor Rothman said, was the advent about 2.5 billion years ago of bacteria engaging in photosynthesis, which paved the way for the later appearance of animals by belching fantastic amounts of oxygen into earth's atmosphere.

Methanosarcina is still found today in places like oil wells, trash dumps and the guts of animals like cows.

Alarmingly, the same effects are starting to happen today as a result of global warming caused by man-made carbon emissions.

Analysis of geological carbon deposits reveals a significant boost in levels of carbon-containing gases - either carbon dioxide or methane - at the time of the mass extinction.

But volcanic eruptions alone could never have produced the amount of carbon laid down in rock sediments during this period, the researchers say.

"A rapid initial injection of carbon dioxide from a volcano would be followed by a gradual decrease," Dr Fournier said.

"Instead, we see the opposite: a rapid, continuing increase.

"That suggests a microbial expansion. The growth of microbial populations is among the few phenomena capable of increasing carbon production exponentially, or even faster."

It existed before the Permian crisis. But genetic evidence indicates it acquired a unique new quality at that time through a process known as "gene transfer" from another microbe, the researchers said.

It suddenly became a major producer of methane through the consumption of accumulated organic carbon in ocean sediments.

The microbe would have been unable to proliferate so wildly without proper mineral nutrients.

The researchers found that cataclysmic volcanic eruptions that occurred at that time in Siberia

drove up ocean concentrations of nickel, a metallic element that just happens to facilitate this microbe's growth.

Dr Fournier called volcanism a catalyst instead of a cause of mass extinction - "the detonator rather than the bomb itself".

"As small as an individual micro organism is, their sheer abundance and ubiquity make for a huge cumulative impact. On a geochemical level, they really do run the planet," he said.

The Permian mass extinction unfolded during tens of thousands of years and was not the sudden die-off that an asteroid impact might cause, the researchers said.

The most famous of earth's mass extinctions occurred 65 million years ago when an asteroid impact wiped out the dinosaurs that ruled the land and many marine species.

There also were huge die-offs 440 million years ago, 365 million years ago and 200 million years ago.

PA, Reuters