Rahul WishardImpact craters are geologic structures formed when a large meteoroid, asteroid or comet smashes into a planet. The surfaces of the Moon, Mars and Mercury, where other geologic processes stopped millions of years ago, record this bombardment clearly. On the Earth, however, which has been even more heavily impacted than the Moon, craters are continually erased by erosion and redeposition as well as by volcanic resurfacing and tectonic activity. Thus only about 120 terrestrial impact craters have been recognized, the majority in geologically stable cratons of North America, Europe and Australia where most exploration has taken place.
Meteor Crater (also know as Barringer Crater, 1.2 km in diameter and 170 m deep) in Arizona was the first-recognized terrestrial impact crater. It was identified in the 1920s by workers who discovered fragments of the meteorite impactor within the crater itself.
Image: Shane Torgerson, 2010
There are about 191 confirmed impact craters around the world.
Large terrestrial impacts are of greater importance for the geologic history, for example, a large asteroid or comet hit the Earth at the end of the Cretaceous Period 66 million years ago resulting in environmental crisis triggered by the gigantic collision and the abrupt demise of a large number of biological species including dinosaurs. Some scientists suggest that large meteorite impacts might be the metronome that sets the cadence of biological evolution on Earth – an unproven but intriguing hypotheses.
There are 5 confirmed impact craters in India:
1. Dhala crater (Formed by an asteroid impact 2,500 million years ago, located near Dhala village, Shivpuri district, Madhya Pradesh.The diameter of the crater is estimated at 11 km, extending upto 25 km, and is considered as the largest in India as well as between the Mediterranean and Southeast Asia)
2. Lonar crater and lake (Formed by a meteorite impact that occurred between 35,000 and 50,000 years ago, located at Lonar in Buldhana district, Maharashtra. Although a study published in 2010 gives an age of 0.57 million ± 47,000 years. Lonar Lake has a mean diameter of 1.2 km and is about 137 m below the crater rim. The meteor crater rim is about 1.8 km in diameter. It was identified in 1823 AD by a British officer named C.J.E. Although a study published in 2010 gives an age of 0.57 million ± 47,000 years. This greater age is in line with the degree of erosion of the crater rim.
The crater has an oval shape. The meteorite impact came from the east, at an angle of 35 to 40 degrees.
There is a small circular depression at a distance of around 700 m from the main lake, believed to be caused by a splinter of the meteor that hit the ground to also make a crater)
3. Luna crater (Formed by meteorite impact occurred around 2000 BC, located near Luna village, Rann of Kutch, Gujarat. The relatively smaller crater is circular and has a diameter of 1.2 km and its lowest point is only about 2 m. The site is located just a kilometre from the remains of an ancient Harappan-era settlement. The event finds mention the tenth book of the Rig Veda has a reference to ‘heavenly charcoal’ falling in a place called ‘Irina’.
4. Ramgarh crater (Formed by an meteorite impact 750,000 million years ago, located near Ramgarh village, Baran district, Rajasthan. The crater is 3.5 km in diameter and is visible from a distance of 40 to 50 km, as it is located on a circular hill about 400 m high.
The crater was first visited in 1869 AD by Mallet of Geological Survey of India. The Bhand Deva Temple, a 10th-century Shiva temple in the style of the Khajuraho Group of Monuments, is located near the centre of the crater)
5. Shiva crater (The geologic structure consisting of the Bombay High and Surat Depression is hypothesized to be a 500 km impact structure. The structure lies beneath the Indian continental shelf and the Arabian Sea west of Mumbai. It is argued that the Shiva Crater was formed around 65 million years ago, about the same time as a number of other impact craters and the Cretaceous–Paleogene extinction event leading to extinction of the dinosaurs. It is estimated that this proposed crater would have been made by an asteroid or comet approximately 40 km in diameter.
At the time of the Cretaceous–Paleogene extinction, India was located over the Réunion hotspot of the Indian Ocean. Hot material rising from the mantle flooded portions of India with a vast amount of lava, creating a plateau known as the Deccan Traps. It has been hypothesized that either the crater or the Deccan Traps associated with the area are the reason for the high level of oil and natural gas reserves in the region.
Earth scientists in general remain unconvinced that the “Shiva Crater” is indeed an impact crater.
The proposed Shiva Crater and other possible impact craters along with the Chicxulub have led to the hypothesis that multiple impacts caused the massive extinction. Other theories have argued that since the Chicxulub impact is believed by some researchers to have occurred earlier than the extinction of the dinosaurs and 75% of plant and animal species on Earth, Shiva’s impact was enough to cause the mass extinction by itself)
Chicxulub crater, Yucatán Peninsula, Mexico
The following are the speculated impact craters in India:
1. Dal Lake Crater (It is hypothesized that Dal lake in Srinagar is infact an impact crater turned lake, further research is pending)
