Methods

All samples were analysed using the JEOL 8900 L electron microprobe at the Department of Earth and Planetary Sciences at McGill University. Samples were mounted on glass slides using double sided carbon tape and coated with ~ 150 Å of carbon. Samples mapped for starch were stained with I before carbon coating2, with half of the sample masked to provide a blank reference (see Figure 3). Experimental conditions were 15 kV and 20 nA with 3 um pixel spacing. Dwell times per pixel were 100 ms, and where backgrounds were measured dwell time per pixel was 50 ms.


Figure 3 Mapping samples, light and dark squares indicate mapped areas.