Using light to describe the ancient world

Archive for the ‘General’ Category

Online resources

SpectroscopyNOW

SpectroscopyNOW is a site devoted to all aspects of spectroscopy, from Atomic to X-ray. It highlights all of the new developments in spectroscopy, and includes a chemometrics section. If you search “fossil” you will find an article about the work of William Schopf.

 

RRUFF

The RRUFF project is a database of mineral spectra, including apatite, aragonite and calcite, and other minerals that grow on or in fossils. From the website, “The RRUFF™ Project is creating a complete set of high quality spectral data from well characterized minerals and is developing the technology to share this information with the world”. RRUFF is a very useful resource for comparative Raman and XRD data.

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The List

I have just started a new feature – The List. On this page, linked right at the top, will be an evolving list of all the papers I encounter that have applied spectroscopy to fossils. This will be a reference guide, and the means for tracing trends and developments.

Spectroscopy of fossil bone Part 1: Phosphate

Vibrational modes (dance moves) of phosphate.

Bone is a matrix of organic matter supported on a mineral scaffold. Bone mineral (biological apatite) contains an abundance of calcium, as we all know, but is mostly phosphate by weight. Phosphate is an anion formed from one phosphorus atom bound to four oxygen atoms – the oxygens try to keep as far away from each other as possible, and give phosphate a tetrahedral arrangement. Although the oxygens are tethered to the central phosphorus atom, they are free to move, and move they do. Oxygen dance moves are well choreographed and can be prompted under the right conditions. For example, all of the oxygens can stretch away from the phosphorus at the same time (ν1), or they can all bend in the same direction (ν2), or two can stretch while the other two contract (ν3), or two can bend one way while they other two bend the opposite way (ν4). Each of these dance moves is called a vibrational mode, and may be induced when phosphate is irradiated with a laser. Over the next few posts I will explore how these vibrational modes report important information about the preservation of fossils.

Recommended reading

Smith, E. and Dent, G. 2005. Modern Raman Spectroscopy, a practical approach. John Wiley and Sons (Chichester). Find it on Google Books

The Light Fantastic

Light from the setting sun is reflected from the glass and absorbed by the wine. The sun would soon set, but scattered light from beyond the horizon would allow us to see the wine glass for a while longer.

Spectroscopy is a science built on three key interactions between light and matter. Light is interacting with all of the matter you can see through the process of Reflection. Light from a source, possibly the sun, reflects from your shirt, and is detected by your eye. Not all of the light survives the encounter though – your shirt greedily traps some of the light in the process of Absorption. Sunlight is made up of a mixture of photons with different energies. Different photons have different wavelengths, which we see as different colours when they are separated apart, but appear as white light when all mixed together. White light adopts colour when it interacts with a pigment; some light is absorbed by the pigment and removed from the white light mixture. When you look at your shirt, the colour you see is the result of absorbed photons and reflected light. What you may not notice while looking at your shirt, but you can test, is the process of Scattering. Try this: sit in a room without the lights on, on an overcast day, with the curtains or blinds pulled. The first thing you will notice is all of the little points of light coming into the room – the corners of the curtains, light from under the door. The second thing you will notice is that you can see the objects in the room, even though they are not being directly lit. This is because light coming into the room is being scattered off all of the surfaces. Consider scattering a sort of recycled reflection (scattering is also known as diffuse reflection).

So there you have it – three interactions between matter and light that form a basis for studying the ancient world. I would highly recommend the Wikipedia pages on Reflection, Absorption and Scattering for more details.

 

Shining light

A 514nm laser used to irradiate samples for Raman Spectroscopy

A spectroscopic laser (514 nm)

Welcome to Illuminating Fossils, a new blog  showcasing the incredible world of spectroscopy as applied to the remnants of ancient life. Spectroscopy uses energy – including visible light – to provide chemical and structural details of samples. The light that spectroscopists shine on samples tells them what they are made of, and how they were put together. Studying ancient life with energy is an infant science, and we will begin our family album by looking at the steps taken so far.

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