Posted in biology, physics, technology

Humans vs Neanderthals – the mammoth competition that ended in extinction

After thousands of years, the reason for the Neanderthal’s extinction has finally come to light. Using isotopic analysis, it was found that both ancient humans and the Neanderthals were in direct competition for their main food source – woolly mammoths.

The first anatomically modern humans are thought to have colonised Europe around 43,000 years ago, forcing the Neanderthals into extinction approximately 3,000 years later. So, why did Homo sapiens succeed where the Neanderthals could not? There are many hypotheses, but by far the most common is that the diet of anatomically modern humans was more varied and flexible, allowing them to consume fish. However, a new study by the Senckenberg Research Institute and the Natural History Museum has blown this out of the water.

The hypothesis that early humans had a more varied diet has been fuelled by the observation that they had a higher abundance of 15N in their bone collagen when compared with Neanderthals. This difference was chalked up to the addition of freshwater fish to the diet, a conclusion that has been refuted by  Prof. Dr. Hervé Bocherens and his colleagues at the University of Tübingen.

There are two main explanations for the presence of 15N in ancient human remains – a high concentration of 15N in the natural environment, especially concentrated in the meat of large herbivores whose meat makes up the majority of the diet, or a significant dietary contribution from a single prey with higher 15N abundance than prey usually found at archaeological sites (e.g. fish or mammoth meat).

Until recently, it has not been possible to distinguish between the dietary impact of freshwater fish and mammoth as both are known to have high 15N abundance and comparable levels of the 13C isotope. Due to the overlapping isotope abundances, accurate estimation from collagen alone was not possible. However, due to recent advances in stable nitrogen isotope analysis on individual amino acids, it is possible to identify the exact origin of the proteins consumed by the ancient humans.

In the study, the remains of three anatomically modern humans were examined. Found in the Belogorsk region of south Crimea, the remains were examined for phenylalanine (as a baseline) and glutamic acid (as an indicator of trophic position). Alongside the humans, the fossils of variety of prey animals found during the excavation were also investigated. Using the percentage ratio of the 13C to 15N isotopes present in the proteins of both the ancient humans and their prey, the scientists could establish the main components of their diet. Using this data, it was found that mammoth meat made up around 40-50% of the Homo sapiens’ diet. Isotopic studies of western European Neanderthals have also pointed to a significant consumption of mammoth meat, placing them in direct competition with the ancient humans.

This fierce interspecies competition for resources placed the Neanderthals under extreme stress. Without unrivalled access to their main food source – woolly mammoths – they were unable to forage enough food to survive. Whether due to superior hunting ability, increased brain size or other factors, Homo sapiens emerged on top. Without competition, humans thrived and have persisted until today. However, this is not the case for the poor woolly mammoths.

Tabitha Watson

Image Credit: [http://www.nhm.ac.uk/content/dam/nhmwww/our-science/news/2014/mammoth-model-753.jpg]

Posted in physics, science

How do headphones work?

With a market value set to reach $15.8 billion by 2025, chances are you own a pair of headphones. However, the odds of the average person knowing how they work are significantly worse.

At the most basic level, all speakers are made up of three main constituents: a cone (sometimes referred to as a diaphragm), a coil of wire and a permanent magnet. As shown in the main image, the cone is attached to the coil. The permanent magnet is situated within the coil.

Electricity is fundamental to the function of headphones – when it flows through the coil, it becomes an electromagnet. If the flow of the electricity is altered, the electromagnet either attracts or repels the permanent magnet. This combination of both attraction and repulsion induces motion in the coil, causing the cone to move. These movements generate vibrations (a.k.a. soundwaves) in the air – much like those produced by banging on the skin of a drum. As discussed in my previous post ‘How do we hear?’, the ear detects these vibrations and converts them into signals that can be processed by the brain.

Once the soundwaves are being produced, factors such as volume and pitch are controlled by the strength and frequency of vibration. In order to generate a louder sound, larger and more powerful vibrations are required. Pitches are determined by the frequency of the soundwave. The frequency is defined as the rate of the wave, illustrated by Figure 1. Whilst pitch is altered simply by increasing the power of vibration, frequency is governed more by the size of the speaker. Hence, huge subwoofers produce much better bass than a tiny in-ear headphone.
frequency1

Figure 1

Although humans are capable of hearing many different types of sound, headphones and other sound-systems can typically only produce two: monoaural and stereo. Monoaural is when the sound only comes from one source, such as someone speaking. This is the type of sound encountered during a phone conversation or from an old radio. Stereo sound is encountered when two speakers generate slightly different vibrations in order to emulate a 2D soundscape. Have you ever had a song begin in one headphone and move across to the other? That’s an example of stereo. Whilst it is possible to generate 3D sound artificially, it is a lot more time consuming. To be effective, speakers must be placed around the audience and each must play subtly different things. Currently, the only place that this is practical is for ‘surround-sound’ in cinemas. Though, given the passage of time, it may well become a future household staple.

Tabitha Watson

Image Creds: [http://www-cdn.sciencebuddies.org/Files/7472/6/speaker-diagram.png

images.tutorvista.com/cms/images/83/frequency1.PNG]

Posted in chemistry, physics, science

How do things glow in the dark?

It is relatively common nowadays to see a plethora of glow-in-the-dark products across a vast spectrum of items. Although most regularly found in toys and watches, there seems to be no end to the types of item that can be modified to glow. So, how does this phenomenon occur?

Firstly, it is important to pin-point what is meant by the term ‘glow-in-the-dark’. In this instance, it is used to describe luminescence. Luminescence is the emission of light from a source that has not been heated; due to the lack of heat, it is a form of spontaneous emission. If heat is involved, then the phenomena is labelled incandescence and is not considered spontaneous. There are several different ways in which luminescence can occur, including through chemical reactions, electric currents and the compression of certain types of crystal.

The type of luminescence encountered most commonly in day-to-day products is phosphorescence. Phosphorescence is a specific type of photoluminescence that involves molecules called phosphors. Usually transition metals or rare earth elements, phosphors absorb energy from electromagnetic radiation and emit it as visible light over timescales between nanoseconds and hours. Funnily enough, phosphorus is not defined as a phosphor – it is chemiluminescent as opposed to photoluminescent.

Underpinning the ability for photoluminescent materials to emit light is quantum mechanics. When a photon collides with the phosphor and is absorbed, it excites an electron to a higher transition state. When the electron drops back down to its usual state, it releases a photon whose energy exactly corresponds to the size of the gap between the levels. This is what we perceive as the emitted ‘glow’. In the majority of photoluminescent events, this excitation and relaxation of electrons occurs over extremely short timescales, often in the region of nanoseconds. This is known as fluorescence. However, when phosphors (such as zinc sulphide and strontium aluminate) are involved, phosphorescence can emit light over much longer periods of time. This is the key difference between fluorescence and phosphorescence – the time taken to re-emit the energy.

So, why is it that phosphorescence can occur over such long timescales? Again, it’s all based on quantum mechanics. As you may know, ‘allowed transition states’ and ‘forbidden transition states’ are key within quantum mechanics. These, along with a rather expansive set of rules, govern the movement of electrons in their respective shells. In normal circumstances, when a ground state electron is excited to a higher energy level, it will transition into an exited singlet state. This means that it has paired up with another electron with an opposite spin (i.e. obeying the Pauli Exclusion Principle). The Pauli Exclusion Principle states that no two particles with a half integer spin (such as electrons) can occupy the same orbital at the same time (think of people on a bus – ideally, people aim to sit on an unoccupied pair of seats before going to sit next to a stranger).

However, in some cases (as in phosphorescence), the excited electron will transition into an excited triplet state. This is where things get a little complicated. In an excited triplet state, the excited electron is spinning parallel to the ground state. This is called intersystem crossing. As having the same spin is considered ‘forbidden’ within quantum mechanics (again, due to our friend Pauli), it means that the excited triplet state electron is in a bit of a pickle. The ‘forbidden’ transitions are less kinetically favourable than the ‘allowed’ transitions, meaning that it is more difficult for the electron to relax back to its normal ground state. This prolongs the relaxation progress, ensuring that the glow of released photons lasts for longer.

So, there it is. Objects glow in the dark due to the phenomena of phosphorescence – the process by which electrons are excited to ‘forbidden’ quantum spin states. As the electrons are allowed to relax, they emit a photon of light corresponding to the distance between the energy levels, producing the subtle glow which is now associated with watch hands and plastic stars. In conclusion, the entire glow-in-the-dark industry is reliant upon a small group of rebellious electrons not doing what they should. Pretty neat, huh?

Tabitha Watson