Understanding the history of impacts of asteroids on Earth is important, as large impacts play a critical role in the evolution of Earth’s natural systems such as its atmosphere, biosphere, and hydrosphere. Unfortunately, there is very little evidence of impacts from the beginning of Earth’s history 2.5 to 4 billion years ago, known as the Archean Age, because geological processes such as erosion and plate tectonics have erased the distinct features of the craters. In fact, the oldest confirmed impact structure on Earth, the Yarrabubba Crater in Australia, is 2.23 billion years old, roughly half of Earth’s total age. However, the impact ejecta found on Earth are between 2.6 and 3.47 billion years old. As a result, scientists have only small pieces of evidence to reconstruct the environment of a young and heavily bombed Earth and understand how impact processes have contributed to Earth’s evolution. The region of Maniitsoq in West Greenland has recently attracted interest as several studies have hypothesized that it represents an impact structure 3 billion years old, almost 750,000 years older. than the crater of Yarrabubba. A recent study, led by Chris Yakymchuk at the University of Waterloo, Canada, sought to test this hypothesis.
The study generated several new datasets, including chemical analyzes, age data, and microscopic mineral structures from more than 5,000 zircon grains collected in the Maniitsoq area. Taking a closer look at these datasets, Yakymchuk and his colleagues concluded that the evidence does not support the hypothesis that the Maniitsoq region in West Greenland is an impact structure. For example, the ages obtained for a sample originally thought to be produced by impact fusion were too young to be associated with the impact event assumed to be 3 billion years old. Additionally, minerals that typically deform at the atomic scale when subjected to an impact event did not have these unique structures in the samples studied. Finally, the study concluded that their observations could be explained by the long duration (about 80 million years), the high temperature metamorphism and the magmatic activity that would have affected the region. By rejecting the hypothesis that the Maniitsoq region in West Greenland represents a 3 billion year old impact structure, the study confirms that the 2.23 billion year old Yarrabubba impact years in Australia is the oldest known impact structure on Earth. These results highlight the elusiveness of Archean Age impact structures and serve as a motivation for future studies that seek to improve our understanding of early Earth evolution through its impact assessment. READ MORE