Tuesday, 9 November 2010
Wednesday, 11 August 2010
This is a photo of an average sized species of Foraminifera sieved from chalk at Ballard Down. A 0.01 mm grid has been superimposed on the image in order to enable measurements to be made.The thickness can be estimated from the quite globular chambers.Effectively the organism is actually somewhat wedge shaped;thicker at the top than the bottom.
Please click once on the image in order to enlarge it.
This entry is an effort to estimate the number of Foraminifera tests in a 15 cm cube of chalk from Ballard Down Dorset Uk.
I have always thought that such efforts were rather a waste of time, because there are so many variables when dealing with fossil material 95million years old. Never the less its really surprising what sort of a number one can come up with, but it is just these figures no matter how inaccurate, that engage and surprise the general public.How do we find an average when there are so many eroded tests to sample ?
I have just taken a typical surviving test mounted in a canada balsam strew that is neither too small nor too large by observation. The initial measurements were taken with a Beck eyepiece graticule graduated in parts of a mm. I shrank and expanded the image until it was exact according to my record through the microscope.
Since the chambers of the test are quite globular, I measured the radii of each chamber and calculated the volume of each, using the formula (Radius cubed times PI times 4/3) ; the formula for the volume of a single globe. The results were then added together. My selected "average" test made 0.00044107 cu mm which is pretty small .
This was then divided into the volume of the 15cm block cube which is hopefully 3,375,000 cubic mm. The result is rather nicely 7,651,846,645 which is fascinatingly enough very nearly the human population on Earth not so long ago. I think we are currently way past this figure and well over the 8 billion. This means that the calculation for the whole of Ballard Down would need a considerable amount of paper, and my old computer would certainly blow a fuse in the process.
When I consider the effect of potential inaccuracies on this figure it can more probably become greater than smaller.
I fully appreciate that numerous other and perhaps better methods can be used to arrive at a figure. I tried several alternatives but came back to the above with all its faults. BD.
Sunday, 14 February 2010
This refers to an article of mine in Micscape UK QV on a mounted needle.
Yes I knew it!!!!!!!!.............. I should have spent more time writing about the point.
that was the really the point of the aticle I suppose.!!!................
I have to write that at first I could not find a tube that was 1mm external so I used 1.5mm diam. and had to shape the point by rotating it when it just protruded from my mark one version . I used a combination of a fine triangular file and very fine sandpaper to make a blunt point of about 0.3mm diam. at the end but the very end was flat and burnished flat and then painted with Matt black.
The relatively. large forams like Elphidium I glued on the round end with water based Gum tragacanth so that any part of the periphery could be imaged. by rotation .====Then I decided that a flat platform was also a good stage for angular shots of apertures .so I filed one side flat to create a flat stage 2mm long which bit into the end of the cylinder to a width of 0.3mm. I had to buy a brass vernier measure .
When I found my 1mm external hollow brass tube in Holland the diameter of the insert was 0.3mm and that was the right size without treatment except when I wanted the inclined stage. All the measurements were based on my wanting to look at the Foraminifera tests. and in particular those of +_ 500um diam.
So briefly Gumming with Gum Tragacanth on the end of the 0.3mm insert rod is how I now do it.
Centralisation on the end so would be trial and error whilst under the microscope as the tests are drying off..
Its up to you folk to develop it. I can see that some with a large(ThicK) mechanical finger on thir stage (ie the Clip)may need another slide glued underneath but that is not a problem. Also for reflected light only then a layer of paint underneath might look neater and avoid little glares!.
Also Please read info on the supply of 1mm hollow tubes
NOTE for integration into the text or at the end.
A SUPPLY OF 1MM HOLLOW BRASS TUBES.
At first I could not find any tube less than 1.5mm in diameter in the
UK. I had to use thicker glass up to 1.5mm but it
was much more difficut to cut neatly.
Even on line scanning on US sites, I found nothing; they still seem to
be using imperial measure anyway. Then I began to look at the EU and
sure enough there was the 1mm I was looking for on a Dutch site for
The internal hole was 0.3mm which was just right. A pack of several
tubes was less than £10 with postage and took only 3 days BD.
Best wishes Brian Darnton. Swanage UK
Sunday, 7 February 2010
Recent Foraminifera of the Dorset Shores.
These delightful microscopic shells grace the tidal waters of Dorset. They are not true shells however but are more closely related to the antediluvian Amoeba of our school text books. In order to protect themselves from the multitude of hungry creatures in the sea, they have simply developed a spiral shell like structure called a test, though the smaller ones prefer the simplicity of an urn shape. In the open ocean, the more globular species float with the plankton and it is these free spirits that form deep deposits on the sea bed. Given a few million years of pressure they will become chalk, as at Ballard Down. They are mainly constructed from some form of crystalline chalk and others look externally almost like porcelain.
In the great lagoons of Poole Harbour they enjoy the muddy less-salty water by means of an adaptation. With a shortage of the minerals of the open sea, they create a bag of chitin-like material and bond silt and sand particles onto this to make their tests. This can be seen in the illustrations on the top row, these are called arenaceous tests and are often very beautiful indeed.
Each species has a preferred level of saltiness and temperature, so seen together they are useful environmental indicators. At Swanage and Weymouth the mortalities are washed up at the most westerly edge of the bays with the sea-coal fragments. This alternate black and white banding is a good clue to their location. In the harbours and lagoons like The Fleet they are to be found around the edges near the high tide marks. as well as embedded in the mud itself.
The Foraminifera of warmer waters can be larger than one millimetre but most of the Dorset ones are from a tenth to a half of a millimetre in diameter and provided they are well illuminated they can be seen with a good hand lens or a simple microscope.
This phylum of single celled members of the Protista are just a tip of the iceberg sample of what exists in the seas around our world, when examined with a microscope B.D.