Asteroids are rocky remnants from the early Solar System, chunks of stone and metal that range in size from pebbles to mountains. Most of them orbit peacefully in the asteroid belt between Mars and Jupiter, but occasionally gravitational forces can nudge them toward Earth. The largest asteroid, Ceres, is almost 1,000 km across, while the one that likely killed the dinosaurs was roughly 10 km wide. Even relatively small asteroids can cause tremendous damage for example, the space rock that created Arizona’s famous Meteor Crater was only about 45 metres across, yet it generated a crater just over 1km wide.
This image of Meteor Crater in Arizona has a resolution of 2 meters per pixel, and illumination is from the right. Layers of exposed limestone and sandstone are visible just beneath the crater rim, as are large stone blocks excavated by the impact (Credit : National Map Seamless Server)
When asteroid sized rocks strike Earth, the tremendous pressure and heat can often melt surface rocks blasting them back up into the atmosphere. Here they cool and fall back to Earth as glassy droplets known as tektites. Australian scientists led by PhD student Anna Musolino and Professor Fred Jourdan from Curtin University have discovered some tektites which are rather unusual because of their chemistry and age. They are thought to be about 11 million years old, making them different to all other known tektite groups. Most remarkably, they have so far only been found in an area within South Australia.
To understand how rare this find is, there are only five different tektite fields known; the four ‘classic’ ones known for nearly a century, from Central Europe (14 million years old), North America (35 million years old), Ivory Coast (1 million years old), and a large area spread from China to Australia (780,000 years old) and a more recently discovered field in Central America (800,000 years old). This Australian discovery represents just the sixth such field ever identified.
What makes this discovery particularly intriguing is the missing crater. Although the impact must have been immense to generate the tektites, the team have still not yet managed to locate the crater! It’s not unusual for craters to become hidden over millions of years of weathering or geological activity. They can simply be eroded or even buried under volcanic deposits hiding them from view.
The famous Chicxulub crater in Mexico, which killed the dinosaurs 66 million years ago, was similarly hidden until the 1970’s when geologists found it buried under limestone and ocean sediments. The crater is estimated to be just under 200 km in diameter, and has since filled with ocean sediment.
Free-air gravity anomaly over the Chicxulub crater structure – coastline and state boundaries shown as black lines (Credit : J. Klokočník, J. Kostelecký, I. Pešek, P. Novák, C. A. Wagner, and J. Sebera – Klokočník, et al)
The presence of tektites provides us with crucial insights into Earth’s impact history. Each tektite field represents a significant asteroid strike, creating a timeline that helps researchers understand both the frequency and scale of these events. This data is invaluable for assessing the ongoing risk of future asteroid impacts too and, while most asteroids pose no threat to Earth, the geological record preserved in tektite fields reminds us that large impacts have occurred regularly throughout history. The discovery of this new Australian tektite field helps scientists develop better models for predicting and potentially mitigating future civilisation threatening strikes.
Source : Cosmic Glass Found Only in Australia Reveals Ancient Asteroid Impact