In a groundbreaking study published in the journal Tectonophysics, scientists have discovered what is believed to be the largest impact structure on Earth. The Deniliquin structure, located deep beneath the Earth’s surface in southern New South Wales, has a diameter of 520 kilometers, surpassing the previously thought to be the largest impact structure, Vredefort in South Africa. This discovery sheds new light on hidden traces of Earth’s early history and provides valuable insights into asteroid bombardment of the planet.
Erosion and concealment:
The history of asteroids hitting the Earth still remains largely hidden due to various factors. One such factor is erosion, where gravity, wind, and water gradually erode soil material over time. An asteroid impact produces a crater with a raised core, similar to the way a drop of water splashes upward from a transitional crater when a pebble falls into a pool. However, this central raised dome can erode over thousands or millions of years, making it difficult to identify impact structures.
Burial and subduction:
Impact structures can also be buried by sedimentary rocks or disappear as a result of subduction, a process in which tectonic plates collide and sink beneath each other into the Earth’s mantle layer. These factors make it even more difficult to identify and study these structures. Nevertheless, recent geophysical discoveries have begun to reveal evidence of impact structures formed by asteroids that could reach tens of kilometers across, revolutionizing our understanding of Earth’s evolution through time.
Implications for early Earth history:
The discovery of impact “ejecta” – material ejected from the crater during an impact – has provided crucial clues about Earth’s early history. Researchers believe that the oldest layers of these ejecta, found in deposits of early landforms around the world, may mark the end of the late heavy bombardment of Earth. Evidence suggests that the Earth and other planets in the solar system experienced intense asteroid bombardment until about 3.2 billion years ago, and that collisions have been sporadic since then. Some of these major impacts have been correlated with mass extinction events, such as the asteroid impact that led to the extinction of non-avian dinosaurs 66 million years ago, which is explained by the Alvarez hypothesis.
Asteroid impacts in Australia:
The Australian continent and its predecessor Gondwana have been subjected to numerous asteroid strikes throughout history. There are currently 38 confirmed and 43 potential impact structures in Australia, ranging from small craters to large, fully buried structures. The recently discovered Denilikin structure is the largest known impact structure and is of great scientific value.
The discovery of the Deniliquin structure as the world’s largest impact crater opens new possibilities for understanding the early history of Earth and the role of asteroid impacts in the formation of our planet. This discovery underscores the importance of ongoing research to uncover hidden traces of our past and expand our knowledge of Earth’s geologic evolution.