Was India hit by an ET object that caused mass extinction?
doi:10.1038/nindia.2019.157 Published online 27 November 2019
The Deccan Trap region in India, one of the world’s largest volcanic provinces, possibly suffered a massive extra-terrestrial impact that triggered mass extinction of species on Earth around 250 million years ago, a geological study suggests1.
The event called Permian-Triassic (or P-T) mass extinction is believed to have eliminated up to 96% of all species on Earth. Also called the “Great Dying”, it remains an interesting piece of puzzle for geologists. There are multiple theories around how it may have been triggered — from volcanic eruptions to a massive seafloor methane belch, from gradual changes in oceanic or atmospheric chemistry to a catastrophic asteroid impact.
Geologists led by Gopalakrishnarao Parthasarathy at the National Institute of Advanced Studies, Bangalore were analysing samples from the volcanic cover in the Deccan Plateau in west-central India when they found something unusual — 'microspherules' or tiny condensed droplets of molten and vapourized rock deposited on Earth as thin layers. Such structures are mostly generated during an impact or impact-induced volcanism.
These samples had been dug out from sediments 338 metre below the volcanic cover through a borehole drilled in the epicentral zone of the 1993 Killari earthquake in Maharashtra, which had killed over 10000 people. They also analysed pollen grains embedded in these samples.
“The discovery of irregular-shaped spherules and similarly composed basement rocks provides good evidence that they were generated through impact,” Parthasarathy, a former chief scientist at the National Geophysical Research Scientist in Hyderabad, told Nature India. By studying plant pollens and spores (called palynological investigations) found in the borehole samples, the researchers confirmed the age of these sediments as "Early Permian" or 298-295 million years ago (Ma).
The team investigated the microspherules through scanning electron microscope and used energy dispersive X-ray diffraction to decipher the images, morphology and elemental composition. They also studied the nature of the vapourized impacted rocks. The studies revealed that the spherules here were similar in composition to those from the continental lower Gondwana sediments of India, as well as other landmasses of the Gondwana Supercontinent. Gondwana is the name for the southern half of the supercontinent composed of South America, Africa, Arabia, Madagascar, Sri Lanka, India, Antarctica, and Australia that existed some 300 million years ago.
The iron composition of the spherule and its chlorine content were almost same as the basement rock. This, the researchers say, suggests the possibility of an extraterrestrial impact over the Indian terrain during the Gondwana sedimentation period.
The occurrence of microspherules below the Deccan volcanic cover justifies the speculation of an extraterrestrial impact, says Ramesh Singh, a geophysicist at Chapman University in the US who has studied the Killari earthquake extensively. "Unfortunately, we do not have many boreholes around Killari,” he says.
Though studying spherules in the dust particles is a new approach, some geologists are sceptical about its correlation to an impact. "We can't draw a conclusion about a large event (mass extinction) by merely studying a few particulates. Further support for the 'giant impact' theory is needed," says Naresh Ghose, retired professor of geology at Patna University.
N. V. Chalapathi Rao of the Centre of Advanced Study in Geology at Banaras Hindu University, Varanasi agrees. "First there has to be a sedimentary basin resulting from an impact – only then the sediments can be preserved.”
The researchers admit that at this stage, their inference may look far-fetched and more evidence may be needed to prove it. "But the fact is that till date, not many terrestrial impacts are documented and many of them may have gone unnoticed, especially in terrains like Deccan Traps, which are covered by a thick suite of volcanic rocks," they point out.
1. Parthasarathy, G. et al. First observation of microspherule from the infratrappean Gondwana sediments below Killari region of Deccan LIP, Maharashtra (India) and possible implications. Geosci. Frontiers 10, 2281-2285 (2019) doi: 10.1016/j.gsf.2019.04.005