Prof. (Dr) YP Kundal
The meteoroidal and asteroidal showers have played an important role in the evolutionary history of earth, shaping the geological landscape, affecting the evolution, migration and even extinction of some of the organisms, generation of some of the important minerals, creation of some impact crater lakes and sub-surface hydrocarbons. Apart from these, the asteroidal fragments /meteorites have also helped mankind in shaping the religious beliefs and fears in the minds of different communities all over the world.
The human interest and curiosity to know more about the meteoritic impacts grew faster in past century following the suggestion that a large impact event caused the extinction of about 50 per cent of the then living species about 65 million yrs ago, including the dinosaurs from all over the world in general and Gujarat, in particular. So, roughly after 65 million yrs (K-T episode), once again, this area had witnessed the cosmic activity in the form of meteoritic showers about 5,000-6,000 yrs ago causing a large scale havoc, destruction and migration of the survivors of Indus-Valley Civilization. The intensity of the meteoritic showers, as can be understood from the impact signatures marked on the ground, was of the type like a hail-storm and so much so that even an inch of ground surface was not left untouched.
The Google Earth Image: The triangular Ajwa Lake, Gujarat (Size limbs 5000 mt, 4500 mt, 3500 mt ) is formed by meteorite of the size of appx 200 mt diameter and the surrounding smaller black dots are the talavs are formed by the impact of smaller fragments. The size of each visible pond is more than 100 mt diameter and is thought to be formed by fragments of 5 -10 mt diameter. The gaps between the ponds in the photo were also sprayed by the smaller fragments and the resulting craters are invisible on this scale.
Like the way, we see our infancy stage or past in our kids and old stage or future in our fathers, in the same way, earth, also has three stages of life i.e. infancy, youth and mature stage. The infancy/past stage can be seen in the Venus and the future/old stage in the Mars. You see, ever since the time of our birth, our bodies have preserved the signatures of all the hitting objects in the form of wound marks on the different parts of our bodies, in the same way, mother earth is also supposed to preserve the signatures of all the impacts of cosmic origin. On the Moon, since there is no weathering or erosion, so, the entire record of impacts of extra-terrestrial bodies is fully preserved in the form of lunar craters but in the case of earth, the prolonged weathering and tectonic processes have eroded, hidden or deformed many a older record of impacts and that’s why the surface of earth does not give us the complete record of meteoritic bombardments which have happened during the different periods/eras.
Since, the nature of crustal skin of earth, gravity, polarity and even the atmosphere has undergone a constant change, hence, the nature of signature marks of the hitting objects cannot be expected to be the same throughout the evolutionary history. Therefore, many a meteoritic objects which had attacked the then baby earth could have easily penetrated the thinner and softer crustal skin causing a wide scale volcanic activity.
Also, the shape and size of the impact marks depends on the angle, speed, size, nature of object plus crust and hence, the vertically hitting objects create the rounded craters, whereas, the obliquely hitting ones form elongated and asymmetrical signature marks.
There are different types of lakes all over the world but the lakes of the Gujarat have a unique morphology which is hardly found in any other parts of the earth. For example Somnath Sarovar, Kankariya Lake, Chandola Lake, Naroda Lake, Samayalpura Lake, Vadsagar Lake etc all have circular outline and island like feature at the centre. The circular shapes and the presence of island -like structures called as central -highs are the only features which can be created by the angels i.e. extra-terrestrial objects from the space. The circularity is the result of vertical hit of the meteorites and the island like feature, the central highs are the result of bouncing and relaxation of compressed rocks. The objects hitting the earth at lower angles result in the formation of asymmetrical and shallow wetlands.
History records show that some of the Sarovars, lakes and Talavs in Guarat are thought to have been dug by the erstwhile rulers, kings and saints but the fact of the matter is that craters were pre-existing there and the rulers had/have simply beautified them by erecting parapets, laying pavements and in some cases, creating the artificial is isthmuses i.e. a narrow stretch of land to reach the central islands. Today, most of these island-like structures have been developed into parks, religious places and guest houses etc.
These crater-lakes, being of astronomical origin, are really the gifts of God in Gujarat and hence, provide us the real life time happiness, experience and feeling of pleasure in walking, talking and boating on the places of such a great cosmic incidence.
As the nature of earth`s crust, target rocks, gravity, atmospheric pressure and its composition has not always been the same throughout the evolutionary history of earth and accordingly, the nature of meteoroids, their velocity, the amount of atmospheric resistance and the angles of hitting have also not remained the same throughout the impacting history of meteoroids. Therefore, the natures of impact signatures marked on the surface of earth are always supposed to vary from time to time and place to place. It has been researched that the size of a crater is about 20 times more than the size of meteoritic body. So, measuring the diameter of many a crater lakes in Gujarat, it has been found that the meteoritic fragments ranging in size from dust particles to 200 mt diameter, had attacked this area during the times of our primitive Indus-valley and Mohenjodaro-Harrappan civilisations. Such is the vast no of these countless impact craters that we can name the state of Gujarat as The ‘State of Million craters’.
(To be continued)