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Photo: Coring at sea in the Antarctica, courtesy R. Rickaby
The relationship between air temperature and the amount of carbon dioxide in the atmosphere (pCO2) is a ‘hot’ topic for scientists – as it can help them understand both past and future climate change. Much of the evidence for past climate change is found in the geological record, where varying temperatures and pCO2 may be derived from a variety of isotopic and chemical signals recorded in fossils of past organisms. But how good are these records? Do they faithfully reflect past climates? Can scientists rely on empirical measurements without understanding the biological mechanisms that underpin them? This research will be highlighted during a session of the American Geophysical Union Fall Meeting on Tuesday 4th December.
These uncertainties are driving the research of Professor Rosalind Rickaby and her team at the University of Oxford in the GRACE project. With ERC funding, they are investigating the ‘living geological record’ – by deciphering the climate signals recorded in the genetic make-up of living organisms. Throughout life’s evolution, genes accumulate mutations, some of which confer advantages for organisms to out-compete others against a backdrop of environmental change. Her challenge is to read these genetic signals as a ‘ticker tape’ of climate change.
Marine micro-organisms use the ‘Rubisco’ enzyme to fix carbon as they photosynthesise. By investigating the genetic sequences in modern Rubisco, Prof Rickaby and her team can look back in time and see when changing ambient conditions, such as temperature and pCO2, caused positive selection for the Rubisco enzyme to mutate and adapt. This will help improve understanding of the implications of isotope ratios for signalling climate change, and also increase knowledge of how these phytoplankton organisms control the distribution of carbon in the oceans through geological time and into the future.
The team’s research is turning up some exciting results which will shortly be published. While the focus of the work is on the last 65 million years, Rubisco genes have revealed strong signals from the Precambrian era, 0.5 to 1 billion years ago. This was a time of major events: the atmosphere was very different and evolving; it was a time of major glaciations – culminating in the ‘snowball earth’; and at the end of this period, 540 million years ago, the number and diversity of living organisms exploded – it was the time when life on earth really got going. The results from GRACE so far demonstrate that the history written in genetic material from living organisms may reach back much further into the distant past than expected.