Spherule Sample (IMAGE) Southwest Research Institute Caption An SwRI-led study updated bombardment models based on small glassy particles, known as impact spherules, that populate multiple thin, discrete layers in the Earth’s crust, ranging in age from about 2.4 to 3.5 billion years old. Spherule layers — such as the one shown in this 5-centimeter, 2.6-billion-year-old sample from Australia — are markers of ancient collisions. Credit Courtesy of UCLA/Scott Hassler and Oberlin/Bruce Simonson Usage Restrictions Images/videos may be used by the media and the public for educational and informational purposes only License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.