Wednesday, 31 October 2012

Searching for the origins of Life on Land by Tim Kearsey

How our ancestors (4 limbed vertebrates) came out of the swamps and adapted to life on land some 360 million years ago is still poorly understood, despite what adverts for Irish Stout may suggest! We don’t know how lungs, ears and other adaptations for land evolved (it appears legs evolved in the water).The main reason for this is there is a gap in the fossil record covering this critical interval in our evolution, known as Romer’s Gap.

Over the last two weeks I have been doing the first bit of fieldwork as part of a large 4-year project with scientists from the Universes of Cambridge, Leicester, Southampton, and the National Museum of Scotland on a set of unique locations in the Scottish Borders which are yielding fossils which could fill in this gap.  Some tantalising glimpses have already been found but in the next 4 years we hope to shine a torch on this pivotal stage in the evolution of life.

My job over the last two weeks was, with Carys Bennett from Leicester University (see her blog at www.tetrapodworld.com), to measure and describe the sedimentary rocks in which the fossils were found.

Dr. Sarah Davies, Dr. Carys Bennet and Prof. John Marshall Sampling at sunset – a must on tidal sections.

Hang on - I thought you were looking for fossil! Why do you need to look at the rocks as well??

Yes, the fossils are being looked at (by the team from Cambridge University) but to understand the evolution of these animals the context has to be understood too.
What I was doing is very similar to what an archaeologist does; a ancient piece of jewellery may be interesting on its own, but only by understanding the buildings and layers that it was found in can you work out how old it was and what it can say about the type of people who may have owned it.
The same is true of sedimentology;   by understanding the sediments we can firstly work out fundamental things like which fossil is older than another. This will then allow us to track the evolutionary changes as these creatures adapted to life on land. Secondly, through reading the rocks we can understand the environment in which these vertebrates were living, and how it changed through time.  This may help to explain why they came on to land rather than just how.

Fossilised roots (the black lines in the white sandstone) – key to building up a picture of the environment the fossils lived in

So what were you doing?

To start off with I have been sedimentary logging. A sedimentary log is an illustrative representation of the sedimentary rocks in the sequence you are studying. It is in effect a column that is drawn from oldest rocks at the bottom to youngest at the top, with the rock units stacked on top of each other in sequence (see Cary’s blog for more details www.tetrapodworld.com). Also we have been sampling for a range for fossil plant spores (palynology) and to understand how the rocks formed better using a range of microscopic and chemical techniques which will help us understand the environment the rocks were formed in.


Me (left with a dGPS) and Sarah Finney collecting specimens (courtesy of Rob Clack)

This is only the first stage in a large programme of investigations. In 2013 we will be drilling a 500 metre borehole as well as doing many more fossil excavations to hopefully finally understand how, and why, our ancestors came on to land some 360 million years ago – Watch this space for more updates.

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