In a paper published in the April 23 online issue of the esteemed journal Proceedings of the National Academy of Sciences (PNAS), scientists propose that supposedly-alien geological features called black mats are, in fact, of terrestrial origin.
Before this study, these structures were regarded as evidence of prehistoric cosmic impacts. However, it would now seem that they are nothing more than clumps of dust originating right here on Earth.
One of the main implications of this study is that it will rekindle the debate as to whether these asteroid impacts actually triggered recent mass extinctions, or not, Space reports. The issue is far from settled, and so the international scientific community is bound to discuss it in detail for a long time to come.
The last major extinction in Earth's history was the Cretaceous-Paleogene (K-T) event, which occurred some 65.5 million years ago, and wiped out the dinosaurs. But it was not the last instance when this happened. A smaller extinction occurred around 12,900 years ago.
During this event, most of the large mammals that lived throughout North America went extinct, as did an ancient civilization called the Clovis people. At this point, the Younger Dryas impact hypothesis is being used to explain their disappearance.
This set of hypothesis proposes that an asteroid impacted Earth at this time, leading to increased levels of the metal iridium in atmosphere. The chemical is usually available only in small amounts in nature. Discoveries of magnetic spherules and titanomagnetite grains seemed to augment this theory.
But investigations recently conducted on impact markers in sediment layers – from southwestern United States and the Atacama Desert, in Chile – determined that signs of cosmic collisions were evenly spread throughout the geological record, and could not be found in higher concentration in layers corresponding to 12,900 years ago.
“Many of us familiar with wetlands and black mats thought that the 'impact markers' might be concentrated by natural processes,” United States Geological Survey researcher Jeff Pigati says.
“We were certainly excited, however, to see the consistency of our findings across continents and different time periods. It really shows how pervasive the markers can become in such environments,” he goes on to add.
“There is a wealth of information stored in these sediments that can be used to determine how hydrologic systems responded to abrupt climate change in recent times. This is especially critical in arid environments in which water resources are severely taxed already,” the investigator concludes.