A Record of Fossil-Fuel Use (image) Brown University Share Print E-Mail Caption A section of the 100m ice core taken in Greenland in summer 2006. Scientists studied nitrates -- the deposited form of nitrogen isotopes -- in the core to determine that fossil fuel burning has altered the global nitrogen cycle. Credit Meredith Hastings, Brown University Usage Restrictions None Share Print E-Mail 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.