New evidence suggests the world's largest known asteroid impact structure is buried deep in southeast Australia
In recent research published by myself and my colleague Tony Yeates in the journal Tectonophysics, we investigate what we believe—based on many years of experience in asteroid impact research—is the world's largest known ...
The Deniliquin structure, yet to be further tested by drilling, spans up to 520 kilometers in diameter. This exceeds the size of the near-300km-wide Vredefort impact structure in South Africa, which to date has been considered the world's largest.
Hidden traces of Earth's early history
The history of Earth's bombardment by asteroids is largely concealed. There are a few reasons for this. The first is erosion: the process by which gravity, wind and water slowly wear away land materials through time.
When an asteroid strikes, it creates a crater with an uplifted core. This is similar to how a drop of water splashes upward from a transient crater when you drop a pebble in a pool.
This central uplifted dome is a key characteristic of large impact structures. However, it can erode over thousands to millions of years, making the structure difficult to identify.
Structures can also be buried by sediment through time. Or they might disappear as a result of subduction, wherein tectonic plates can collide and slide below one another into Earth's mantle layer.
Nonetheless, new geophysical discoveries are unearthing signatures of impact structures formed by asteroids that may have reached tens of kilometers across—heralding a paradigm shift in our understanding of how Earth evolved over eons. These include pioneering discoveries of impact "ejecta", which are the materials thrown out of a crater during an impact.
This map shows the distribution of circular structures of uncertain, possible or probable impact origin on the Australian continent and offshore. Green dots represent confirmed impact craters. Red dots represent confirmed impact structures that are more than 100km wide, whereas red dots inside white circles are more than 50km wide. Yellow dots represent likely impact structures. Credit: Andrew Glikson and Franco Pirajno