Originally this was going to be one of those corny 1 of April spoofs, hence the title, for all those devotees who revel in such matters but then I decided this was not a subject for such brevity. Robert Hooke is one of two founding fathers of microscopy and should be respected for not only being such but as probably one of the most learned and accomplished scientists of his time. During January 1665 Hooke published, through the Royal Society of which he became Curator by Office, his book entitled Micrographia. Throughout he makes detailed accounts and observations of common objects viewed through one of his microscopes in addition to superbly drawn illustrations which must have amazed everyone who thumbed its pages. He had presented to the world a view of a microscopic world never seen by anyone before.

 

 

 

Above is a representation of Hooke's microscope, modelled in Blender 3D, from the line drawing (Schem:1, Fig:5 and Fig:6) depicted in Micrographia. For all its inaccuracies and artistic licence, visualising a 3D representation helps put the individual components into context.

 

 

 

 

The loneliness of the long-distance beachcomber. A bleak, deserted, windswept beach along the west Wales coastline.

 

Whilst we are all aware of sea shells on the sea shore and probably without exception have taken home the odd one or two as mementoes of a particular holiday, how many of us appreciate that more often than not we are tramping over myriads of shells we didn't even know were there. Above is a photograph of a delightful sandy beach along the Ceredigion coastline; at low tide miles of flat sand with occasional patches of ripple marks. At some time or another throughout the year most flat, shallow-gradient beaches exhibit white streaks running parallel to the sea. Sometimes these streaks can be very extensive, as seen in the photograph above, which is a perfect example of the natural grading of sand by wave action where light material is 'panned' or sedimented above heavier particles of the sand itself. When examined with a hand lens, the content of these streaks will be seen to comprise largely of a miscellany of broken shell fragments and sea urchin spines. When examined more closely though with a microscope, a multitude of sub-millimetre shells comes into view. 

 

 

Mixed foraminifera tests (shells) collected from the beach above.
Width of image represents 4.4mm

 

These shells are the remains of microscopic organisms known as foraminifera which belong to the phylum of Protozoa that includes paramecia and amoebae. These organisms are an important component of marine plankton and upon their death the shells (more correctly known as tests) sink to the sea floor forming vast deposits. The word foraminifera means hole-bearing as the tests of most species are perforated with holes through which the amoeboid organism extrudes pseudopodia used for trapping food particles in the water column.  

 

 

     

Detail of tests showing foramina (perforations).

 

 

 

 

When we use a magnifying glass to look at an insect or a piece of a flower we like to say its been magnified 10 times, or if we look at a fly’s foot with a microscope we might say it’s 200x larger; it’s been magnified 200 times. It’s the way we make sense of what we are looking at and how we might describe it to an interested someone looking over our shoulder.

When it comes to looking at a micrograph, be it printed in a book or viewed on a computer monitor, we really need to know how much larger the subject is in the micrograph as compared with that in real life. Stating magnification is often meaningless as it changes whenever the image is viewed at a size other than at the original capture dimensions and is why a Field of View dimension is more meaningful as suggested in the previous blog.

The human eye is a biological form of a simple camera with a single biconvex lens and a variable aperture at the front but with a light sensitive screen, the retina, at the back rather than film. Light striking the retina creates electrical impulses that flow to the brain for interpretation into a recognisable image.

If two small objects, such as a couple of grains of sand, are placed on a plain background almost touching each other and viewed from a distance of around 25cm, providing the distance between them is not less than about 0.25mm, with average eyesight they should be just visible as two separate entities. If the objects were a little closer together or being viewed from a little further away they would be seen as a single object and be described as being unresolved. It is upon this principle that a photograph printed in a book or newspaper is based. When examined with a hand lens, such a photograph is exposed simply as an array of dots and is seen as such because it has been resolved into individual points by the increase in magnification. However, to the unaided eye the individual dots are too close together to be resolved and consequently merge into one another to produce a pattern of light and dark, the photograph.

If all a hand lens could do was to magnify what the eye could see then there would be very little point in using one as it would not show anything more than was already visible to the eye but within physical limits of the instrumentation in use, magnification does more than this. It increases resolution; in our example, it not only enlarges the two grains of sand but also the space between them allowing the grains to be more easily observed as separate entities. However, if the primary magnification, i.e. the original magnification used on the microscope, is too low to resolve the space between two points they will still be seen as one. No matter how large an image is printed it will not show any more detail as the initial magnification was too low to capture the relevant information. Magnification beyond a point where additional detail is revealed is called empty magnification.

As an example, the pair of micrographs below show the identical region of the gullet and associated cilia of a paramecium, a uni-cellular organism found in ponds. Both have the same field of view (FoV = 0.043mm) but there is considerable difference in quality between the two. Image ‘A’ has a primary magnification of x20,000 whilst image ‘B’ was extracted from an image with a primary magnification of x2,000 (original micrograph at end of this blog).

 

 

At its original primary magnification, the micrograph below shows the entire organism and resolves all detail necessary for its intended purpose, specifically to illustrate the wave motion of cilia.

An area of the low magnification image was selected and enlarged to give the same field of view as image ‘A’ with a magnification of x20k. Since the field of view for both images is the same, the magnification for each image as they appear on the page must also be the same. However, the primary magnification of image ‘B’ is insufficient to resolve the detail revealed in image ‘A’ which has a primary magnification an order of magnitude greater.

 

 

However, everything in life comes at a cost. Whilst image 'A' provides a lot of data regarding fine detail, the low magnification micrograph of the entire organism gives us a contextual view that might otherwise be difficult to interpret from high magnification alone.

 

 

 

 

 

The magnification often accompanying an image in a book, usually expressed in the form as (say) x1,500 is included purely as a guide to give the reader an indication of the degree of primary enlargement used to reveal the given amount of detail. However, in a sense it is both meaningless and misleading. Consider the two micrographs below.

 

 

Scent scale or androchonium of male Large White butterfly (Pieris brassicae).

 

The upper micrograph is twice the size of the lower and the original greyscale image, directly from the microscope, is considerably larger than either. The original magnification is x9,820 but neither image on this page has a magnification this high. Many publications, hard copies or digital, will have the original magnification quoted but unless the image has been reproduced at exactly the same size at which it was originally captured the figure will be incorrect. Scientific papers usually have a bar mark on the image representing a given length (e.g 250um) and no matter at what size the image is reproduced the bar mark will always represent that stated length.

A very convenient way of determining magnification is to state the width of the horizontal field of view (FOV) of the micrograph. In the examples above both micrographs have the same FOV of 61.4um (0.061mm) and providing the image does not get cropped during subsequent publication this always remains true. It makes no difference if they are being viewed on a laptop, tablet, mobile phone or have printed them out, both images still have the same FOV.  It is clear however the magnification of the larger image must be greater than the smaller one. The field of view gives the width of the image as it was in real life before being magnified.

As an example, FOV of 100um (0.1mm) means the full width of the image being viewed was in real life 0.1mm. The image on your laptop might be 7.5cm or, more conveniently, 75mm wide but this still represents the original FOV of 0.1mm and is therefore 75mm / 0.1mm times larger than life size, a magnification of x750. If the same image was being viewed on a wide-screen television at one metre wide the magnification would equate to x10,000 (1000mm / 0.1mm) whilst the FOV remains the same.

 

 


Microplastic (polyethylene) particles extracted from Garnier PureActive anti-blackhead deep pore wash.

 

 

Microplastic particles extracted from Johnson & Johnson Blackhead clearing daily scrub (left) and Tesco cucumber face scrub (right).

 

Microplastics are currently defined as "plastic particles smaller than 5mm in their longest dimension" (1) but those used in cosmetics preparations are considerably smaller than this and in the photomicrographs above are at least tenfold smaller.  This definition is likely to be modified in the future as 5mm is hardly 'micro' but was chosen as an upper limit to include small but easily visible fragments found in the environment, in particular on beaches and in beach sand. No lower limited has yet been set.

It is an immutable fact that no matter where one is standing on the Earth water always flows downhill. This ultimately means that just about all the water flowing in the world's rivers ends up in the world's seas and oceans and by extension, most of what is in the water whether dissolved or suspended also ends up in the oceans. We are all aware of the pollution problems caused by plastic bags, bottles and other plastic packaging but how many of us over the past few decades have considered that by merely going through our morning ritual of washing with exfoliating preparations and brushing our teeth we may have become unwitting contributors to global marine plastic pollution?

Thanks to the cosmetics and personal care industry that is exactly what has happened(2). Not necessarily out of malevolence but simply through ignorance, ill thought out or thoughtless product design and the desire for greater profits. 

 

 

Many cosmetic and personal care products include in their list of ingredients polyethylene which is in the form of micro plastic particulates and is incorporated into body scrubs, facial cleansers and some toothpastes as a mild abrasive. The particles are not biodegradable, are easily flushed into the waste water system but due to their extremely small size are not trapped and removed by the standard filtration systems at waste water treatment plants(3). As a consequence thousands of tonnes of micro- or nanoplastic particles, directly from personal care products, find their way into the seas and oceans annually adding to the hundreds of millions of tonnes of microplastics already in existence.

A major disadvantage with plastic is it's not biodegradable and is also very resistant to degradability under natural conditions. Just about all we produce ends up as waste that has to be dealt with. In 2013, 300 million tonnes of plastic was manufactured globally, 57 of which were manufactured in the EU. "Studies showed that 40% of plastic waste goes to landfills, 14% is recycled but 32% ends in the marine environment as litter. The Earth‘s oceans were found by selective surveys of waste to contain millions of tonnes of plastic pieces, mostly in the form of microplastics".(4)

Polyethylene ((IUPAC name: polyethene or poly(methylene))) has a specific gravity of between 0.91 to 0.96 meaning it floats in water. In the marine environment the result of this is that it circulates in the water column with zoo plankton. It is a hydrophobic material and behaving like a sponge it "is liable to concentrate hydrophobic persistant organic pollutants (POPs), which have a greater affinity for the hydrophobic surface of plastic compared to seawater".(5) POPs are known to bioaccumulate through the food web. The smaller the microplastic particle the greater the surface area-to-volume ratio and the greater the contamination with POPs. At sub millimetre sizes, micro-particles are being ingested by the co-existing zooplankton which in turn are being preyed upon by larger organisms. Plastic particles with a toxic payload are entering the food chain and the higher up the chain an organism is the greater the concentration.

 

Scanning electron micrographs of microplastic particles isolated from exfoliating personal care products.
Boots Skin Clear daily face scrub Tesco cucumber face scrub

 

 

Garnier PureActive anti-blackhead deep pore wash Johnson&Johnson Clean & Clear blackhead clearing daily scrub

 

 

 

If you want to be thoroughly depressed by marine plastic pollution in general have a look at the 3-part YouTube video "Garbage Island: An Ocean Full of Plastic

 

 

References.


1.  Proceedings of the International Research Workshop on the Occurrence, Effects, and Fate of Microplastic Marine Debris.

NOAA Marine Debris Program, National Oceanic and Atmospheric Administration, U.S. Department of Commerce, Technical Memorandum NOS-OR&R-30

January 2009.


2. Contributing to marine pollution by washing your face: Microplastics in facial cleansers.

Lisa S. Fendall, Mary A. Sewell.  Marine Pollution Bulletin 58 (2009) 1225–1228

 

3. Transport and fate of microplastic particles in wastewater treatment plants. Steve A. Carr, Jin Liu, Arnold G. Tesoro.

Water Research 91 (2016) 174-182

 

4. Global Plastic Waste and Oceans’ Pollution. Million tons of plastic waste have gone missing in the world oceans?

Athanasios Valavanidis. Department of Chemistry, University of Athens, University Campus Zografou, 15784 Athens, Greece.

Scientific Report, 26 May, 2016

 

5. The physical impacts of microplastics on marine organisms: A review

Stephanie L. Wright a, Richard C. Thompson, Tamara S. Galloway

Environmental Pollution 178 (2013) 483-492

 

 

 

Imagine a time and a place when calculators, computers, digital cameras and horror of horrors, mobile phones didn’t exist. Indeed, if you had a telephone it came attached to a house by a long black cable and the only thing you could do with it was make a telephone call. Imagine also there being only 3 television channels to watch, in black and white of course, with no chance of recording a programme in the unlikely event of a clash as even an affordable, commercially available video tape recorder was a futuristic dream by some years. CD and DVD were just letters of the alphabet, digital and binary were terms used solely by academic mathematicians who could only cope with two numbers and the nearest thing to software was hardware, a shop down the road that sold coal shovels. Nor would you have a computer or tablet on which to read this. A place of nightmares for most early 21st century youngsters who find it impossible to live without their mobile phones, iPads and Xboxes. No, this was not millions of years ago when dinosaurs ruled the world, it was how life was in 1965 on planet Earth.

 

However, during those dark mediaeval times, the Telegraph newspaper published a colour supplement magazine with photographs the likes of which had never been seen before by the general public. A dentist’s drill looking like something a car mechanic might use; a length of double-coiled cable that might have once adorned a hair drier, in reality a filament from a light bulb; a shaft of beard hair resembling the trunk from a New Zealand tree fern and a piece of trawlerman’s net that turned out to be the knitted fibres of a nylon stocking. The images astounded many and certainly fired the imagination of a youngster I once knew to try and follow some form of scientific career. All the micrographs had been produced using a new type of microscope, the first commercially available scanning electron microscope (SEM), manufactured by Cambridge Instruments and marketed as the Cambridge Stereoscan. 

Double-coiled tungsten wire filament from a domestic electric light bulb.
 

The micrographs were stunning and certainly hard won though by modern standards now appear dated. These days the use of scanning electron micrographs to illustrate or enhance many a literary work is commonplace and almost obligatory but the age of digital photography has to a considerable extent and much regret, devalued their status. With so many of the population owning a digital camera (or perhaps more accurately, an image capturing device) in one form or another ready to ’snap’ the most trivial of subjects, the average person now attributes little if any value to most images. The work and expertise required to produce any high-quality image is lost or ignored. A consequence of this is that many images are being stolen and freely distributed over the worldwide web without any consideration of copyright, the work or even the cost having gone into producing them.

 

 

Human chromosomes cultured, extracted and isolated from leucocytes (white blood cells). Costing over £1,000 in consumable supplies and many hours of complex work, these images are a far cry from a simple 'snap' taken with a point-'n'-shot mobile phone camera or something similar.

 

 


One of our electron micrographs on the BBKA stand.

 

Glorious sunshine over four days of the Royal Horticulture Society (RHS) Spring Festival at Malvern brought out a record 100,000 visitors to the showground with 19,000 visiting on the first day alone. The surrounding roads were brought to a standstill for miles around taking hours to drive just a few miles, no doubt much to the annoyance of local residents unable to get out of their own drives.

We had a number of micrographs displayed at the 'beekeeping experience' on the British BeeKeepers Association stand which were appreciated by the many visitors to the show. There was a lot of interest in them and were something of a talking point. It is always gratifying to have our images appreciated especially when used for educational purposes making the hard work producing them, however satisfying personally, worthwhile.

 

 

 

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Getting close-up and personal with a grain weevil, Sitophilus granarius

 

Consider yourself standing in a large, unlit room. There is no light coming in from anywhere, it’s pitch black and you cannot even see your hand in front of your face. You have no idea of the room’s size or what else is in there. You've left your torch at home and having jumped on the e-cigarette bandwagon you don't even have a box of matches to help you light your way. However, after a bit of Columboesque-style pocket rummaging you find that laser pointer pen you got for Christmas but never really had a use for. It pierces the darkness very effectively and probes the unknown space before you but its narrow beam does nothing to illuminate the room, just a very small, tight spot directly in front. Fortunately your memory remains intact and by systematically sweeping the pen from left to right, top to bottom you are able to build a mental picture in your mind of the room and its contents. Broadly, this is how a scanning electron microscope works but instead of using photons, or packets of light from a laser pen, a scanning electron microscope (SEM) uses electrons; negatively charged sub-atomic particles. As the beam of electrons scans across the field of view the image is built up on either an old style cathode ray tube or, more usually these days, a computer monitor with hard copies being saved as photographs or digital files.

Electrons are produced by an electron gun. Typically this is a V-shaped tungsten wire filament positioned at the top of a column where, under vacuum, it is heated to a temperature at which it glows white hot (about 2,700 deg.C) by having an electrical current passed through it. Negatively charged excited electrons escape from the surface from where they are drawn to a positively charged anode plate by a voltage difference between the two known as the accelerating voltage. The potential difference may be varied considerably by the microscope operator depending upon the nature and sensitivity of the specimen but is frequently in the range of 15,000 to 25,000 volts.

Carrying a negative electrical charge, electrons are affected by electromagnetic fields. By employing a combination of electromagnetic lenses to accurately control magnetic fields along the length of the column, the original cloud of electrons created at the electron gun is focussed into a fine coherent beam. Two deflection coils control the X and Y position, (the left to right, top to bottom sweeping motion in the laser pen analogy) which when used simultaneously scan a specimen line by line, from top left to bottom right. On striking the specimen, relatively low energy electrons (<50eV) known as secondary electrons (SE), escape from the surface of the sample and are scattered in all directions. These are subsequently attracted to a detector that has a small positive electrical charge applied to it.

The collector comprises a scintillator disc, a light guide and photomultiplier tube. Electrons striking the scintillator disc generate a flash of light that is amplified by the photomultiplier. This is then converted into an electronic signal which is displayed on some form of display screen, e.g computer monitor or cathode ray tube. The number of secondary electrons leaving any part of the specimen and striking the detector determines the brightness and contrast of the final image. Fewer electrons are captured from shadow areas, so appearing dark, than from well ‘illuminated’, open areas that appear bright.

Contrary to what one might think, magnification is not actually achieved using lenses but instead by dictating the size of rectangle over which the electron beam is allowed to scan. Since the size of output remains constant, (i.e the computer screen), the smaller the rectangle being scanned on the sample the greater the magnification on the monitor. If the monitor is (say) 400mm wide, at a magnification of x1,000 the actual width of sample being scanned is 400µm (0.400mm) but at a magnification of x10,000 the width of the sample being scanned is only 40µm (0.040mm).

Very low and medium magnification micrographs of Asiatic lily (Lilium asiatic) stigma revealing germinating pollen grains.

 

Perhaps one of the most appreciated advantages of a scanning electron micrograph is the relative ease with which it can be interpreted. They have a familiar realism which makes them easy to relate to even if one doesn’t know exactly what an image represents. Most, if not all of the image appears to be in focus, due to the considerable depth of field associated with the microscope and the subject has a solid, 3-dimensional appearance as clearly demonstrated by the images on this page.

 

 

 

 

These things did - coccolithophores, by the bucket load.

 

Coccolithophores are very small to minute spheroidal, biflagellate, unicellular marine phytoplankton with yellow-brown chloroplasts and characterised by an exoskeleton comprising intricate calcite (calcium carbonate, CaCO3) scales called coccoliths. However, what they lack in size they more than make up for in design beauty. They may also be present in such massive numbers that present-day blooms of the algae, covering vast areas of the sea, are easily visible to low Earth orbit (438miles, 708km) satellites and even make news headlines.

A massive bloom of coccolithophore Emiliania huxleyi in the Barents Sea
off the coast of Norway, August 2011.

The variations in bloom brightness and colour is partly due to its depth.
Emiliania huxleyi can grow luxuriantly to a depth of 50 metres. NASA image courtesy of Jeff Schmaltz

 

 

These modern-day algae have an ancestry dating back millions of years to the Cretaceous period when they too were present in vast numbers throughout that time. As they lived and died their remains fell as marine 'snow' at sedimentation rates often exceeding 10cm per thousand years(1) settling to form a thick mud. Over millions of years these sediments built-up forming deposits tens of metres (hundreds of feet) thick that subsequently became compacted and hardened into a soft, friable rock. This material in turn was uplifted by plate tectonics and together with changes in sea level became exposed then eroded to form the chalk cliffs and landscape synonymous of central-southern and south-east England.


Looking good for ~85.5 million years old.
Scanning electron micrographs of fossil coccolithophores, possibly Coccolithus sp. or Watznaueria sp.
isolated from chalk samples collected at Birling Gap, East Sussex, UK. Though millions upon millions of the organisms lived and died over tens of millions of years, in relative terms, very few intact specimens have survived through to modernity. However, with such huge numbers involved even the survival of a small fraction of a percent means many millions still made it through to present day in one piece. They are extremely abundant despite their miniscule size and perceived fragility which is just that - perceived.

 

Further examples of intact coccolithophores. Left and centre images: scanning electron micrographs.
Right image: high magnification photomicrograph (Oil immersion x100, N.A. 1.35) of isolated coccolithophore. 

 

Two relatively low magnification electron micrographs clearly showing the fossil remains of foraminifera embedded in (left image) and protruding from (right image) the matrix of coccoliths and individual calcite crystals that were once part of coccolithophore exoskeletons. The chalk samples were fractured to expose a fresh surface then freed from loose material with a jet of compressed air.

 

Scanning electron micrographs of detached coccoliths and calcite crystals that once formed structural components of coccoliths.
Sample prepared as above.

 

Surviving intact, coccolithophores poking out from the remains of the relatives that didn't. 

 

It has been reported(2) that population densities of contemporary coccolithophores can reach in excess of 100,000 cells per litre but data vary widely, this figure being somewhere in the middle. Apparently (original source remains elusive) scientists also suggest that coccolithophores are the leading producers of marine calcite estimating that more than 1.4 billion kilogrammes are deposited by them each year as a result of their activity.(3) Towards the end of the 1990s, detached (free-floating) coccoliths reached concentrations of nearly 6 million per millilitre during Summer blooms of the algae in the Bering Sea.(4)

Even if population density and marine biomass alone are taken into consideration, these algae must have played an important role in the past in both carbon and calcium turnover. With climate change (anthropogenic or otherwise) and ocean neutralisation (real of not) the hot topics of the moment, these algae are going to come under ever-increasing scrutiny. They are obviously survivors, they weathered the Cretaceous–Paleogene (K–Pg) extinction event a few years ago and no doubt will see us out, humans, their distant relatives(5) that is. 

 

Calcite crystals and fossil coccoliths frequently contaminate the tests of fossil foraminifera both within the walls and on the surface. This probably suggests that their incorporation into tests is more than simple contamination but that recycling or reuse has taken place.  

 

 

A mind boggling thought to ponder.

Out of curiosity, I attempted one of those pointless calculations to reckon how many intact coccolithophores might be contained within a cubic centimetre. The average diametre of the coccolithophores found to date is about 10µm. Applying the formula (v=4/3.Pi.r3) for the volume of a sphere, we get 524µm3. Since there are 1x1012 cubic microns (i.e. 1,000,000,000,000) in 1cm3, by calculation we get 1.9 billion coccoliths per cubic centimetre. For those who prefer imperial units, 1 cubic inch is equivalent to 1.64x1013 (i.e. 16,400,000,000,000) cubic microns which, dividing by 524, equates to 3.1x1010 (31,000,000,000) coccoliths per cubic inch.

Current guesstimates by the United Nations for human world population stands at around 7.4 billion. This implies there are more than 4 times the number of coccolithophores in a cubic inch of chalk than there are humans currently living on the planet. With deposits hundreds of feet thick and covering an area of hundreds of square miles, consider the volume of chalk in Southern England alone and imagine the number of coccoliths that created the deposits.

 

 

References.

1. Sedimentary Basins: Evolution, Facies, and Sediment Budget. Chapter 5, p.192.  G. Einsele. Springer-Verlag Berlin Heidelberg New York

2. Coccolithophore dynamics off Bermuda (N.Atlentic). Ali T. Haidar, Hans R. Thierstein. Deep-Sea Research II 48 (2001) 1925-1956

3. What is a Coccolithophore? John Weier. NASA Earth Observatory, 26 April, 1999.

4. Changing Currents Colour the Bering Sea a New Shade of Blue. John Weier. NASA Earth Observatory, 30 March, 1999.

5. Will Ion Channels Help Coccolithophores Adapt to Ocean Acidification? Mejia R (2011). PLoS Biol 9(6): e1001087.

Chalk cliffs at Birling Gap near Beachy Head, East Sussex

 

A few years ago, during the Cretaceous period about 145 to 66 million give or take a year or two, Britain was allegedly mooching around at a Mediterranean latitude with much of southern England bathed in a warm, relatively shallow sea that teemed with life. The chalk that forms the cliffs along the south coast, known as the Severn Sisters and Birling Gap, is of the late Cretaceous period about 87 to 84 million years old(1); it is soft, friable and easily eroded by weather and sea action. It is also very rich in fossils. Whilst the macro-fossil remains of life at that time abound throughout the chalk deposits, their numbers pale into insignificance when compared to the mind-boggling numbers of the micro- and especially nano- flora & fauna of the time. Indeed, the deposition of their remains, i.e. the (now) chalk deposits of central-southern and south-east England is in effect just a mega-huge pile of fossils. A pile over 410 metres in places.(2)

 

Chalk from Birling Gap cliffs magnified to show remains of foraminifera, a coccolithophore (red circle),
coccoliths (green circles) and infinite broken fragments of each.

 

To the chemist, calcium carbonate (better known to the rest of as chalk) is an inorganic compound but there can be little doubt that this soft, off-white rock is a very organic material. Ever since receiving a copy of The Observer's Book of Geology as a birthday present when my age was in single digits, I have had an obsession with chalk after leafing through the book and finding a couple of line drawings of microscopic fossils (foraminifera). I was rubbish at finding them at that age and my little plastic 'Merit' toy microscope would never have stood up to the job of showing them well anyway. Living (then) in the south of England though, chalk was never very far away and I would seldom pass up an oportunity to pick up yet another piece of the delightful stuff. Now, with many more years behind me than there are ahead and the 'toys' have become bigger and more expensive, the appeal of chalk has never diminished and with very little excuse and at the slightest opportunity I will still grab a chunk when the chance arises, especially as I no longer live in chalk country.

Armed with a microscope and a lump of the South Downs, fossil hunting can be done easily in the comfort of your home. A piece the size of a walnut will provide rich foraminiferal pickings for many months. Just soak in water for a few days with ocassional shaking, allow to settle then examine the resultant sediment with a microscope. Directly below is a pair of photomicrographs showing a few of the treasures resulting from half an hours worth of manually picking through such simply obtained material. All the micrographs on this page are of fossil foraminifera, an ameoboid organism that secretes a shell (or test) around it as it grows. These are the microfossils of chalk and although less than half a millimetre in size, are however relatively large and considerably more so than the nanofossils (in coloured circles on the above micrograph) that comprise the bulk of the remaining sediment. Almost everything in that micrograph is the fossil remains of microscopic organisms. 

The nanofossils of chalk will be considered in the next blog but are too small to be easily seen with a light microscope and unlikely to be of particular interest to the amateur or casual micropaleontologist.

 

Transmission photomicrographs of fossil foraminifera.
The field of view of each image is 1.34mm 

 

Below are four detailed examples of individually selected fossil foraminifera manually picked from the sediment of a chalk sample collected from Birling Gap, East Sussex, UK. In each group, the micrograph on the left was obtained with a light microscope, the centre image is a scanning electron micrograph of the same specimen orientated as closely as possible to how it was viewed with the light microscope. The right-hand image is a scanning electron micrograph of the same specimen tilted and rotated to show its form more clearly. These sequences emphasise the value of both microscope techniques when examining such specimens.

Fossil remains of Nonion sp.(?)

 

Fossil remains of Nonion sp.(?)

 

Fossil remains of Textularia sp.(?) - a ubiquitous species appearing everywhere in chalk deposits of south-east England.


Fossil remains of Siphotextularia sp.(?). The scanning electron micrographs clearly show contaminant, or possibly re-used, coccoliths.

 

 

 

References

1. http://www.discoveringfossils.co.uk/sevensisters_fossils.htm

2. The Stratigraphy of the British Isles. Rayner, Dorothy H. 1967. Cambridge University Press. London.