Clay haloes preserve ancient fossils: an Infrared view

A UK-US collaboration has shed light on the preservation of ancient microfossils. As outlined in Interface Focus, the presence of kaolinite haloes surrounding the tiny fossils is believed to have kept destructive bacteria at bay, stopping decay. The small molecular differences of the clay around the fossils called for the Synchrotron IR microbeam.

Fossils that are over 500 million years old are extremely rare because early organisms were microscopic, only the thickness of a hair, and lacked hard parts that can resist decay. To understand how these early organisms could be preserved, IR microspectroscopy was performed using the Multimode InfraRed Imaging and Microspectroscopy (MIRIAM) beamline at Diamond Light Source. IR microanalysis allowed researchers to identify at the micron scale the minerals surrounding 800–1,000 million-year-old microfossils, and it was determined that an aluminium-rich clay known as kaolinite was responsible for their preservation. Kaolinite was previously shown to be toxic to bacteria, so its presence prevented the early organisms from being destroyed.

These observations suggest that the early fossil record might be biased to regions that are rich in kaolinite, such as the tropics. Moreover, the lack of animal fossils in these samples, despite having favourable fossilisation conditions demonstrates that animals were yet to evolve 800 million years ago.

Read more on the Diamond Light Source website

Image: Light microscopy images (left) indicating the position of the microfossils (red boxes) and Synchrotron-based IR maps (right) showing the compositional variation of the clay around the fossil (as ratio of 3694 cm^-1 band vs the M-OH region). 

Credit: Data taken at MIRIAM beamline B22 at Diamond.