Gene Yang ‘19

Billions of years ago, during the Precambrian, mudrocks were considered a rare sedimentary deposit in rivers. Then, the colonization of land by plants coincided with an increase in mudrocks, resulting in a significant change in the composition of river sedimentary deposits. While this relationship between mudrocks and plants has been well-established, less is known quantitatively, and even less about why these two events are correlated. In a paper published in Science, Dr. Neil Davies and research student William McMahon from the Department of Earth Sciences in University of Cambridge, quantify the timing of mudrock appearance over the course of Earth’s history.

In geology, stratigraphy columns are linear, one-dimensional representations that describe the rock composition at a certain layer. By compiling a large database of stratigraphy columns obtained from the Archeon eon (3.5 billion years ago) to the Carbonifeous period (0.3 billion years ago), they were able to measure the mudrock composition of each location in each stratigraphy. The results showed that the fractional abundance of mudrocks increased by 1.4 orders of magnitude after the colonization of land by plants. Specifically, mudrocks began to increase during the Late Ordovician (0.5 bilion years ago). This timing is earlier than expected because land plants did not appear until the Late Devonian (350 million years ago). It is not yet certain why this correlation between land plant evolution and mudrock abundance exists, but quantifying this phenomena may be useful in the development of future hypotheses.

References

1. W. McMahon, et al., Evolution of alluvial mudrock forced by early land plants. Science 359, 1022-1024 (2018). doi: 10.1126/science.aan4660.
2. Image retrieved from: https://en.wikipedia.org/wiki/Mudrock#/media/File:GLMsed.jpg