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Bruce Yardley appointed Chief Geologist

Bruce Yardley (Leeds University) has been appointed Chief Geologist by The Radioactive Waste Management Directorate (RWMD) of the Nuclear Decommissioning Authority (NDA).

Chartership news

Chartership Officer Bill Gaskarth reports on a projected new logo for use by CGeols, advice on applications and company training schemes

Climate Change Statement Addendum

The Society has published an addendum to 'Climate Change: Evidence from the Geological Record' (November 2010) taking account of new research

Cracking up in Lincolnshire

Oliver Pritchard, Stephen Hallett, and Timothy Farewell consider the role of soil science in maintaining the British 'evolved road'

Critical metals

Kathryn Goodenough* on a Society-sponsored hunt for the rare metals that underpin new technologies

Déja vu all over again

As Nina Morgan Discovers, the debate over HS2 is nothing new...

Done proud

Ted Nield hails the new refurbished Council Room as evidence that the Society is growing up

Earth Science Week 2014

Fellows - renew, vote for Council, and volunteer for Earth Science Week 2014!  Also - who is honoured in the Society's Awards and Medals 2014.

Fookes celebrated

Peter Fookes (Imperial College, London) celebrated at Society event in honour of Engineering Group Working Parties and their reports

Geology - poor relation?

When are University Earth Science departments going to shed their outmoded obsession with maths, physics and chemistry?

Nancy Tupholme

Nancy Tupholme, Librarian of the Society and the Royal Society, has died, reports Wendy Cawthorne.

Power, splendour and high camp

Ted Nield reviews the refurbishment of the Council Room, Burlington House

The Sir Archibald Geikie Archive at Haslemere Educational Museum

You can help the Haslemere Educational Museum to identify subjects in Sir Archibald Geikie's amazing field notebook sketches, writes John Betterton.

Top bananas

Who are the top 100 UK practising scientists?  The Science Council knows...

Raindrops keep falling...


Precambrian showers constrain the density of ancient atmospheres, but pose problems for the 'faint Sun paradox'.  Ted Nield reports

Geoscientist 22.05 June 2012

If the Sun 2.7 billion years ago was only 85% as hot as it is today, how come the Earth’s surface was so equable? Most proposed answers to this question involve enhanced greenhouse effect, which would also seem to presume a much more dense atmosphere. However, a new study of fossil raindrops suggests the density of the atmosphere at 2.7Ga was much the same as it is today1.

The Sun is a ‘main sequence’ star, whose core density gradually increases with age – so raising the temperature at which its main fuel, hydrogen, fuses to form helium. A Sun with only 85% of modern radiance ought not to have been able to warm our planet to above the freezing point of water; yet, the existence of fossil raindrops – among other things – shows clearly that liquid water did then exist at surface. This problem is known to science as the ‘faint young Sun paradox’.


Proposed solutions to the paradox tend to fall into one of two types – the sort that propose increase greenhouse effect on the one hand, and the sort that suggests the Earth’s albedo may once have been lower. Equable surface temperatures at this time can be explained by invoking high CO2 concentrations, but carbon isotope work on fossil soils suggests that CO2 alone cannot do the trick, requiring nitrogen levels at twice today’s levels as well.

The big problem with these speculations about atmosphere chemistry is that no constraining data exist either on air density at ground level, nor prevailing barometric pressure. Now, a paper in Nature by Sanjay Som and colleagues has attempted to shed light on this problem by comparing fossil raindrops from tuffs of the Ventersdorp Supergroup in South Africa with rain-induced structures produced in the laboratory by water falling on volcanic ash.

The two parameters of importance are raindrop size and terminal velocity. Raindrops form when the initial blob of condensing water reaches a speed at which it flattens and then breaks up. The raindrops’ size is limited to a maximum that is independent of air density; whereas the droplet terminal velocity varies as the inverse of the square root of air density.

So, because the density controls terminal velocity, estimates of this can be converted into density, which in turn can be used to, if not define, at least place limits on likely prevailing barometric pressure. Any difference between velocities inferred from ancient raindrops and those produced in the lab may therefore be telling us about some alteration in climate density.

After comparing the geometry of raindrop impact structures ancient and modern, the authors conclude that atmospheric density at 2.7Ga was probably somewhere between 50% and 105% of today’s values. If this is true, it means that very high concentrations of carbon dioxide and nitrogen may not be invoked to explain the Faint Young Sun Paradox. It therefore seems likely that one or more highly efficient greenhouse gases, such as methane, ethane and carbonyl sulphide, may have been responsible.


  1. Air density 2.7 billion years ago limited to less than twice modern levels by fossil raindrop imprints, by Sanjay M. Som, David C. Catling, Jelte P. Harnmeijer, Peter M. Polivka & Roger Buick. Nature 484,359–362 April 19 2012 doi:10.1038/nature10890