I must first notify all members that the planned lecture on 19th May by Professor Lister on The Life and Death of the Woolly Mammoth has had to be postponed until the 20th October 2005.
Instead, the last lecture of this session on Thursday 19th May will be by Professor Mitchell Berger on Applied Topology; he is in the Department of Mathematics of University College London.
This will start with wine and cheese (£2 each).
The AGM itself will start at 8.45 and will be followed by a scientific entertainment.
The agenda will include the usual reports from Officers and Sections and the Election of Officers and five Ordinary Members of Council for the coming year. Council proposes the following::
|Membership Secretary||Elisabeth Fischer|
|Programme Secretary||Jim Brightwell|
|Ordinary Members||Simon Lang|
Council invites further nominations to the above officer posts and ordinary members; such nominees shall be duly proposed and seconded and have agreed to serve if elected.
It is with great sadness that we have to record the death of Angus McKenzie MBE at the age of 71 after an illness lasting for several months.
Angus was a well respected and long standing member of the Hampstead Scientific Society, having joined at the age of 14 in 1947. He was interested in all aspects of science, in particular, chemistry, radio and above all else, astronomy. As a youthful enthusiast, he was greatly encouraged during the 1950’s by our late astronomy secretary, Henry Wildey.
Angus was born in September 1933 and was educated at St.Paul’s School Hammersmith. He went on to study for City and Guilds in electronic engineering and acoustics, but failing eyesight caused him to abandon the course at the end of the second year. It was typical of Angus, that even the total loss of his eyesight in 1959, did not prevent him from remaining passionately interested in astronomy for the rest of his life. Having joined the British Astronomical Association in his teens, he remained a member until his death and would frequently attend meetings accompanied by his faithful guide dogs Simon and, latterly, Ward.
It is often said that the loss of a sense, such as eyesight, leads to the development of other senses to compensate. In Angus’ case this was clearly demonstrated. He built a career in audio and radio, at first running a recording studio and later becoming an audio and radio consultant. He engineered and produced numerous recordings of classical music and carried out much research into stereo, binaural and quadraphonic sound. He has written many technical papers and given many lectures on topics as diverse as: radio and hi-fi, amateur radio, classical music, astronomy and the London underground railway. He has broadcast on both radio and television and was the author of many books on the subjects of hi-fi and amateur radio.
His great passion for the London Underground, on which he travelled frequently, led him to produce an auditory guide to the system in 1994 which was available free of charge to blind persons. This innovative guide, a kind of ‘sound map’, led the user from station to station providing clues as to their location from the pitch of track noises and the different sounds emitted by tube train brakes. I well remember the lecture he gave to the Society in which he vocalised the different noises made by different makes of tube train and the sounds which they emitted when accelerating, braking and passing over points.
Angus was also a regular speaker and fund raiser for the Guide Dogs for the Blind Association and in recognition for this work he was awarded the MBE in 1997. He was the first blind member of Mensa and was a fellow of the Institution of Electrical Engineers and the Audio Engineers Society.
For many years Angus lived in Finchley in a house crowded with electronic equipment and with shelf upon shelf of records and CD’s, each labelled meticulously in Braille. I always marvelled that he could find a particular recording instantly. He had a talking computer and the house was equipped with a gigantic rotating radio aerial which could be seen from miles away and used by him to communicate with fellow radio ‘hams’ throughout the world.
Angus leaves two daughters, a son and two grand daughters and a multitude of friends who will mourn the passing of man who never let a physical disability get the better of him.
Doug Daniels (Astro. Sec.)
Science in the city. May I remind you of the guided walk to be held on Saturday 14th May, details of which were given in the Christmas Newsletter. Meet the leader, Mike Howgate, at 11am at the entrance to the Museum of London ; nearest tube Barbican. Would those planning to come please let Doug Daniels know on 8346 1056, so that he can inform Mike of the numbers.
We are currently in the grip of an ice age! This may seem a ridiculous statement when we see the mountain glaciers of the world retreating and the talk is all about Global Warming. However, the term ice age, as used by geologists, applies to a whole period during which there is a sequence of glacial and warmer interglacial periods. Our present ice age, sometimes called the Pleistocene Ice Age, has been with us for 3 million years; during this time there have been alternating cold and warmer periods with roughly a 100,000 year period. The ice started to retreat about 20,000 years ago, so we are currently in an interglacial. But, even so, 75% of all the fresh water on the planet is frozen in glaciers.
How do we know all this? Why does it occur? Has it happened before? What does it imply about the future climate? These are questions to which I will try to provide broad answers.
There is today a wealth of evidence from the shapes of valleys, moraine deposits, the grooves and scratches on bed rock, the existence of erratic boulders (rocks found distant from their place of origin), and the spread of chaotic sediments called glacial drift. These signs are not difficult to see, but they were not recognised as the result of glaciers for a long time. The first to do so was Louis Agassiz of Switzerland in the 1830s. He presented his observations and theory in a book in 1840  , including the radical claim that ice had once covered the whole of Europe. Ice ages became one of the fiercest scientific controversies of the 19th century. Eventually, with careful mapping of the deposits and attention to how they sometimes overlapped, geologists came to recognise that there had been several expansions of ice far south in Europe and N. America during the Pleistocene Age.
Fossils provided further evidence that the interglacial periods had been long enough for the recovery of flora and fauna. In particular it was shown that the sea level had been altering due to the volume of water trapped in the glaciers. At the peak of the last glacial period, 20,000 years ago, the sea level was some 120 m lower than now, as shown by fossil corals found at such depths.
Coring the Sea Floor
A problem with the geological observations was the uncertainty in the dates. Coring of the sediments on the ocean floor can answer this. It began with the exploration of the oceans by the Royal Navy’s survey ship HMS Challenger in 1872-5, which traversed all the world’s oceans and made landfall on all the continents, including Antarctica. But all they could do about sediments was to dredge samples. The technique has been developed since by the Swedish oceanographer Börje Kullenberg in the Albatross in 1947-9, using a piston-operated corer to obtain cores up to 15 m in length. One of the scientists on board was Gustav Arrhenius, a grandson of the great chemist Svante Arrhenius who was the first to suggest that the concentration of carbon dioxide in the atmosphere could affect the climate through its ability to trap the solar heat. Gustav showed that the sediment layers were alternately rich and poor in calcium carbonate (from fossil shells); this was later shown to correspond with the large changes in carbon dioxide associated with the glacial-interglacial cycles.
Since then, cores of several kilometres length have been obtained by drilling from the Glomar Challenger and the Resolution. The dating of the cores is assessed by measuring the remanent magnetism and comparing it with our current knowledge of the pattern of reversals in the magnetic field of the earth, as found from sea floor spreading. The time before the present is limited to a maximum of about 200 million years by the destruction of the sea floor at subduction zones.
Very significant measurements can be made of the isotopic composition of oxygen atoms in the fossil shells. Harold Urey, the discoverer of deuterium, had shown that the proportions were changed when the oxygen in the sea changed to carbonate in the shells and that the amount of change was affected by the water temperature; so the cores could provide a temperature record. Cores have shown that the ocean temperatures have gradually reduced over the last 55 million years, with particularly sharp drops at about 35 million years, when glaciation of Antarctica commenced, and during the last 3 million years when it began in the Northern Hemisphere.
Coring the Glaciers
Coring has also been used on the Greenland ice sheet. The cores not only provide information of climate change but contain air bubbles which record the ancient atmosphere. They have demonstrated that the content of greenhouse gases is closely correlated with temperature.
The cores do not go as far back as the ocean sediment cores. Recent ones from the Antarctic go back only 750,000 years. Drilling at the Russian Vostok base was stopped short so that a large subterranean Lake Vostok was not polluted. However it shows that over the last 400,000 years a regular oscillation in both temperature and carbon dioxide levels, with a 100,000 year period. During the cold periods there was more dust, indicative of higher winds during glacial periods.
It is characteristic of ice ages to have cold and warm phases; could this provide a clue to their existence? Agassiz himself showed little interest but in Britain, a hotbed of geological activity, there were many hypotheses. The right answer was proposed by James Croll a self-educated Scotsman. He suspected there was an astronomical cause. Obviously a major determinant of climate was the heat the earth receives from the sun, so he looked into the variations in the earth’s orbit. His definitive book was published in 1875 .
The earth’s orbit is not a circle but an ellipse and the solar distance changes annually. The eccentricity also changes due to the gravitational effects of the major planets, with a period of 100,000 years. It will reduce to nearly zero in about 30,000 years. Also important is the rotation of the earth itself around an axis inclined at present at 23½ ° but, like a top, this tilt precesses due to the combined gravitational influence of the moon and sun. Taking into account the eccentricity of the earth’s orbit, we find a ‘precession of the equinoxes’ with a slightly different period of 23,000 years.
Croll realised that the change in insolation would be rather small and sought ways in which it might nevertheless generate the glacial/interglacial cycles. He calculated the variation in eccentricity over a time from 3 million years in the past to one million in the future and argued that ice ages would only occur when the eccentricity was high; the curves showed regular peaks at about 100,000 years.
By 1912 Croll’s work had been largely dismissed by geologists because it failed to match the estimated ages of glaciation very well. His work was taken up by Milutin Milankovitch, an engineer in the Austro-Hungarian Empire (later to become a Serb), with better data on the sun’s heat and the earth’s orbital and rotational variations. His work was held up during the Great War and was not published, in French, until 1920. He collaborated with the German scientists Köppen and Wegener of continental drift fame.
Milankovitch considered that the amount of tilt of the earth’s spin axis, which actually varies between 22½° and 24½°, could be important and pointed out that cool summers rather than cold winters were what could initiate a glacial. A cool summer would leave snow on the ground to be added to over the winter. He also recognised, as had Croll, that there was a positive feedback from the greater reflectivity of snow returning more of the sun’s heat back to space. His major work  was published in German and an English translation was not available until 1969.
The astronomical theory did not go well however for many years, largely from the lack of time correspondence. It was not until the development of the coring of ocean sediments described earlier with their high quality time-scales that Milankovitch’s predictions were confirmed. Final confirmation came in 1976  from the oxygen isotopic variation of a core over 550,000 years which showed a 100,000 year cycle from the eccentricity change, a 43,000 year cycle from the axis tilt variation and a 20,000 year cycle close to the axis precession cycle.
The Earth’s Past
The development of coring with its clear time-scale has provided a good picture of the Pleistocene Ice Age of the last few million years, but this is but a fraction of our 4½ billion years history. Geologists have however been able to find evidence of consolidated glacial drift lying on top of grooved bed rock of ancient periods; such drift turned to rock is called tillite. Many of these finds are in what are now tropical areas. Geologists now believe that there were at least four major ice ages before the Pleistocene  :
|Permo-Carboniferous||300 my bp|
|Snowball Earth||600 – 800 my bp|
|Early Proterozoic||2.2 – 2.4 by bp|
|Archean||2.9 by bp|
The first of these is of particular interest because Wegener, who worked with Milankovitch, had searched the separate continents for common geological features as a part of his investigation of continental drift. He was struck by the apparently contemporaneous glacial deposits on all the southern continents and noted that a single ice sheet could account for it if the continents were all together and further south. However it was only many years later when his theory had been translated into plate tectonics that his conclusion was seen to be correct. The location of Gondwanaland near the South Pole explains how such glacial records appear in now tropical countries. An estimation of the spread and duration of the glaciation suggests that the total volume of ice exceeded that of the Pleistocene glaciation.
The next listed above occurred near the end of the Proterozoic eon and is actually called the Late Proterozoic glaciation, but is here named Snowball Earth as there is evidence of its being extremely severe, to the extent that glaciation reached low latitudes. The evidence is from remanent magnetic field of low dip angle in the sedimentary rocks. But even if all land areas were glaciated, it doesn’t prove that the sea was frozen. Joe Kirschvink, a geochemist at CalTech, pointed out in 1992 that there are banded iron deposits (BIF deposits) associated with the glaciation. These are quite well known from early in the earth’s history when the atmosphere had little oxygen, but how could they exist when the atmospheric oxygen level was high? Kirschvink argued that it was only possible if the sea was frozen. Without contact with the atmosphere the sea below the ice would become depleted in dissolved oxygen, allowing iron concentrations to increase; when the ice melted contact with the atmospheric oxygen would resume and deposit the BIFs.
Snowball Earth is still a matter of controversy; if it did occur, we have to ask how it terminated, as the global ice and snow would reflect most of the sun’s heat back to space. Kirschvink argued that carbon dioxide in the atmosphere would continue to be supplied from volcanoes but the two main mechanisms for its removal, photosynthesis in the sea and the weathering of rocks on land, would have stopped. The concentration would rise and the green-house effect would melt the glaciers.
There is now further evidence to support the snowball earth hypothesis. Studies of sedimentary rocks in Namibia using the isotopes of carbon rather than oxygen show the cessation of the fractionation by plankton during the glacial interval. Similar results elsewhere in the world suggest a global change. We do not know whether there were earlier episodes of a similar nature, but the absence such an episode later may be due to two factors: that the sun’s radiant heat has been increasing and that in the Late Proterozoic the continents were all in tropical regions. This would have meant more heat reflected from the tropical land (with no vegetation at the time) and less absorbed in the sea.
Our ability to analyse the earlier ice ages listed is much reduced in view of the time elapsed and our ignorance about the locations of the continents. Nevertheless, geologists consider that the Early Proterozoic and Archean ice ages have occurred. The long gap between the former and Snowball Earth, 1.4 billion years, seem not to have any, but we don’t know why.
Recently there have been suggestions for a possible cause of our present Pleistocene ice age. About 50 million years ago the Indian Plate began to collide with the Asian Plate and the Himalayas and the Tibetan Plateau were formed some 35 myrs ago; this is the time when glaciation began in Antarctica. It is proposed that the immense high-altitude area allowed increased weathering, reducing the carbon dioxide and causing cooling. The positive feedback from ice reflecting energy back to space led to today’s ice age.
For much of its history the earth has been very warm, but there is reliable evidence of at least five ice ages, periods of several million years with alternating cold and warmer phases; we are at present in one of the latter. Some of the ice ages may have been extreme enough to cover all the continents and freeze the seas.
It seems that a basic cause for the ice ages is the disposition of the continents on the globe and the greater reflectivity of the land compared with the sea, with its ability to store the sun’s heat. There are two important phenomena conspiring to cause rapid changes to the climate. One is the positive feedback arising from the high reflectivity of snow and ice. The other is the importance of greenhouse gases in keeping the planet warm. Without the continual discharge of carbon dioxide into the atmosphere from volcanoes, we would be a frozen planet.
The technique of coring of sea sediments and ice fields has demonstrated that astronomical effects have a major influence on the variations within each ice age. The variation of the eccentricity of the earth’s orbit is the dominant cycle, of 100,000 yrs.
The burning of fossil fuel by humanity may have a short term effect in terminating the current ice age, though this may well occur anyway as the eccentricity is now reducing. In longer geological terms, the fossil fuels will soon have gone.
I recommend Doug Macdougall’s book Frozen Earth – the once and future story of ice ages for further reading.
Peter R Wallis.
 Études sur les glaciers. Back
 Climate and Time in Their Geological Relations: A Theory of Secular Changes of the Earth’s Climate, 1875. Back
 Milankovitch, Canon of Insolation and the Ice Age Problem, 1941. Back
 Hays, Imbrie & Shackleton, “Variations in the Earth’s Orbit: Pacemaker of the Ice Ages”,Science, 1976. Back
 D Macdougall, Frozen Earth, 2004, University of California Press, London Back
Last updated 28-Jan-2018 contact