The earth sits in space and interacts with it. This isn’t a controversial statement, but we shouldn’t forget quite how recently geologists on earth started to find abundant evidence for interactions with space.
It is fascinating and mind-expanding science, which is why I’ve blogged about it quite a lot.
Meteorite impacts can create great big holds in the ground, but on earth these structures may be quickly eroded. To find more, some believe that we should be looking in the sedimentary record and that many more impact craters remain to be found, hidden away in oil company seismic data.
For large impacts, the energy turns into heat that melts and vaporises rocks. If a big enough hole is made, there will be extensive metamorphic changes to deep rocks due to the pressure release of removing kilometres of rock.
Another way to identify past impacts is to find material thrown out beyond the crater area. This can include thick layers of fragments and glass, called suevite. Molten glass may be thrown up into space, falling again as spheres of glass over a wide area of the earth. These may be quite thin layers in sedimentary sequences. These surely represent the most extensive record of past impacts but not many have been recognised to date, so keep your eyes peeled. For recent impacts, the glass lumps may still lie on the surface, where they are known as tektites. The largest set of tektites is found in a vast ‘strewn field’ stretching from south-east Asia into Antarctica and yet no-one has yet the crater that was surely formed at the same time.
The most inventive method of finding evidence of past impacts is to study ancient myths. Some link myths about ‘fire from the sky’ to impacts that occurred in human history and seek to explain flood myths by a cometary impact.
I recently attended a conference studying the interactions of the earth and space. One big theme was the lovely idea that pieces of the early earth will be found on the moon.Image Courtesy of Nasa