The Extraterrestrial Spell Of Lonar
Thousands of stellar bodies and debris called asteroids and meteoroids pass within striking distance of the Earth every day. They range from the size of dust particles to those spanning kilometres and weighing millions of tons. And each time our planet is struck by a sizable extra-terrestrial body, it leaves its mark in the form of an impact crater on the Earth’s surface. And each one makes for a great story. The most famous one being the theory that talks of a 10 km. wide asteroid that blazed through space, cut through our atmosphere and hit the ground in the Yucatán Peninsula in Mexico to form the 65-million-year old Chicxulub crater that is believed to have triggered the mass extinction of dinosaurs.
Photo: Baiju Patil
We’re are going to talk about a less famous impact crater that formed very recently in terms of the geological time scale. About 40,000 to 52,000 years ago, in what is today a small town in Buldhana district, in the state of Maharashtra, a massive meteor weighing more than a million tonnes struck the Earth with hypervelocity, creating a one of a kind impact crater, 1.8 km. wide and more than 150 m deep. For years, experts debated the origin of this special crater in the basalt rock of the Deccan Plateau. It was considered to be of volcanic origin, or a geobleme if you will, which means formed of terrestrial processes.
In the later half of the twentieth century, further studies and observation revealed its likeness to an extraterrestrial impact crater and experts realized that it was an astrobleme, a crater of an extraterrestrial source. Unmistakable signs such as the well-shaped circular circumference, ratio of the depth to diameter, and especially the characteristic raised rim about 20 m above ground level on the outside of the impact radius proved that it was indeed an impact crater. Another important clue was the presence of fallen debris from the impact of the meteor with the ground, around the site of impact, making up what is called in scientific jargon, as ejecta blanket. The Lonar crater’s ejecta blanket ranges over one kilometer, including the rim of the crater. But, what ultimately proved without doubt the meterological origins of the Lonar crater was the discovery of shatter cones, breccia and maskelynite. Maskelynite is a type of glass that forms when the hypervelocity impact of a meteor or asteroid shocks the plagioclase, a rock-forming mineral, into vitrifying.
Here is where it gets even more interesting and special. The Lonar crater is the only known impact crater in the world to have formed on basalt rock. And the presence of certain rock minerals such as microbreccias and glass spherules in the crater draws close analogies to the geology and crater formations on the moon (Fredriksson K. et al, 1973). Lonar has been able to give us insights into the lunar!(Pardon the wordplay)
Photo: Milind Shirbate
What makes this story still more exciting is what the crater basin encompasses today – a unique ecosystem that cannot be found anywhere else in the world. For starters, the Lonar Crater is now a lake – a landlocked lake about 140 m. below the rim. Small streams and freshwater springs on the shore feed this unusual lake whose water is both saline and alkaline! The alkalinity of the water increases towards the center and harbours microlife that is extremely rare. In 2011, a rare bacterium Bacillus odyssey was discovered in the Lonar Lake. This bacterium, some studies suggest, does not have its origins on Earth and was last recorded from the Mars Odyssey spacecraft in 2004 (Tambekar & Tambekar 2013). This gave a possible insight into the origin of the meteor. A Martian meteoroid perhaps?
Coming back to earth, the precincts of the crater are thrumming with biodiversity! Among the rich belt of plant life that includes acacia, teak and tamarind trees, dwell varied terrestrial wildlife including monitor lizards, deers, bats, snakes and langurs. But, it is the rich birdlife that steals the show. From waders such as shovellers, stilts, wagtails, and ducks to jungle specialists such as crow pheasants, bee-eaters, woodpeckers, parakeets, peafowl, innumerable avian species abound here. For history aficionados, the crater region had a special place in the culture and life of our ancestors who build temples and shrines on the site, which lie dilapidated and forgone here.
Photo: Milind Shirbate
The magic of Lonar is that it is a mystical remnant of a celestial episode that took place thousands of years ago and unifies beautifully with earthly treasures. Who knows what other secrets remain to be unfolded in the depths of this impact crater.
Author: Purva Variyar.