|SCIENCE TRIBUNE||Thursday, March 7, 2002, Chandigarh, India|
Did star-blasts forge mankind?
NEW PRODUCTS & DISCOVERIES
What causes earthquakes?
LONG time ago, a large collection of material masses coalesced to form the earth. Large amount of heat was generated by this fusion, and slowly as the earth cooled down, the heavier and denser materials sank to the centre and the lighter ones rose to the top. The differentiated earth consists of the inner core (radius-1290 km), the outer core (thickness - 2200 km), the Mantle (thickness - 2900 km) and the crust (thickness - 5 to 40 km). Figure 1 shows these layers. The inner core is solid and consists of heavy metals (e.g. nickel and iron), while the crust consists of light material (e.g., basalts and granites). The outer core is liquid in form and the mantle has the ability to flow. At the core, the temperature is estimated to be - 2500°C, the pressure - 4 million atmospheres and density - 13.5 gm/cc; this is in contrast to - 25°C, 1 atmosphere and 1.5 gm/cc on the surface of the earth.
Convection currents develop in the viscous mantle, because of prevailing high temperature and pressure gradients between the crust and the core, like the convective flow of water when heated in a beaker (Figure 2). The energy for the above circulations is derived from the heat produced from the incessant decay of radioactive elements in the rocks throughout the earth’s interior. These convention currents result in a circulation of the earth’s mass; hot molten lava comes out and the cold rock mass goes into the earth. The mass absorbed eventually melts under high temperature and pressure and becomes a part of the mantle, only to come out again from another location, someday. Many such local circulations are taking place at different regions underneath the earth’s surface, leading to different portions of the earth undergoing different directions of movements along the surface.
The convective flows of mantle material cause the crust and some portion of the mantle, to slide on the hot molten outer core. This sliding of earth’s mass takes place in pieces called Tectonic Plates. The surface of the earth consists of seven major tectonic plates and many smaller ones (Figure 3). These plats move in different directions and at different speeds from those of the neighbouring ones. Sometimes, the plate in the front is slower; then, the plate behind it comes and collides (and mountains are formed). On the other hand, sometimes two plates move away from one another (and rifts are created). In another case, two plates move side-by-side, along the same direction or in opposite directions. These three types of inter-plate interactions are the convergent, divergent and transform boundaries (Figure 4), respectively. The convergent boundary has a peculiarity (like at the Himalayas) that sometimes neither of the colliding plates wants to sink. The relative movement of these plate boundaries varies across the earth; on an average, it is of the order of a couple to tens of centimetres per year.
Rocks are made of elastic material, and so elastic strain energy is stored in them during the deformations that occur due to the gigantic tectonic plate actions occur in the earth. But, the material contained in rocks is also very brittle. Thus, when the rocks along a week region in the earth’s crust reach their strength, a sudden movement takes place there (Figure 5); opposite sides of the fault ( a crack in the rocks where movement has taken place) suddenly slip and release the large elastic strain energy stored in the interface rocks. For example, the energy released during the 2001 Bhuj (India) earthquake is about 400 times (or more) that released by the 1945 atom bomb dropped on Hiroshima!!
This sudden slip causes the earthquake.... a violent shaking of the earth when large elastic strain energy released spreads out through seismic waves that travel through the body and along the surface of the earth. And, after the earthquake is over, the process of strain build-up at this modified interface between the rocks starts all over again (Figure 6). Earth scientists know this as the Elastic rebound theory.
Types and Faults
Most earthquakes in the world occur along the boundaries of the tectonic plates and are called inter-plate earthquake (e.g., 1897 Assam (India) earthquake). A number of earthquakes also occur within the plate itself away from the plate boundaries (e.g., 1993 Latur (India) earthquake); these are called inter-plate earthquakes. In both types of earthquakes, the slip generated at the fault during earthquakes is along both vertical and horizontal directions (called Dip Slip) and lateral directions (called Strike Slip) (Figure 7), with one of them dominating sometimes.
Did star-blasts forge mankind?
THEY are the most destructive events in the universe, vast eruptions that rip apart stars and blast radiation across space.
But supernovae may also play constructive roles in the cosmos — recent scientific research has revealed that these stellar annihilations could have had a crucial impact on human evolution.
Two million years ago, just as the earth’s primitive apemen were evolving into big-brained humans, a pair of supernovae explosions occurred near earth, two scientists believe. Our planet was buffeted with blasts of radiation — with devastating effects. "These supernovae would have blown away our protective ozone layer," said Dr Narciso Benitez, of Johns Hopkins University, Baltimore.
"Earth lost its protection against ultraviolet solar rays and for several hundred years the planet would have been battered by intense radiation. All sorts of mutational damage to animals’ DNA would have occurred. New species could have emerged as a result. It is possible Homo sapiens may have been one of these."
A supernova occurs when a hot, dense star burns up its fuel too quickly and suddenly implodes, generating shock waves and intense blasts of radiation across space. When a supernova explodes, it outshines all the other 200 billion stars that make up our galaxy, the Milky Way.
The likely impact of a supernova’s radiation led scientists in the past to speculate that one may have affected evolution on earth. But calculations indicated that fields of interstellar gas would have dissipated a supernova’s radiation and blunted its impact.
However, Benitez and his colleague, Dr Jesus Maiz-Apellaniz, of the Space Telescope Science Institute in Baltimore, now believe that at least two supernovae occurred near earth two million years ago. The first would have blasted space free of interstellar particles; the second would have struck earth at full force, destroying its ozone layer.
"Supernovae are very rare. So two such explosions occurring relatively close together might seem unlikely. However, we have discovered that around this time a group of hot, dense young stars — just the type that turn supernova — passed relatively close to earth," said Maiz-Apellaniz.
"Some of this group — known as the Sco-Cen group — would have got within 100 light years of us, which, astronomically, is not a great distance. Our calculations suggest that two or three of these exploded as supernovae."
In short, earth was hit by an astronomical double whammy — though the discovery that supernova-prone stars passed near earth two million years ago does not, on its own, provide complete proof, as the two scientists admit.
However, further support for the theory, to be published in Physical Review Letters next week, has been found by scientists studying samples of sediments from the Pacific ocean floor. German researchers recently uncovered an isotope of iron known as iron-60 in ocean bed samples laid down about two million years ago. "Iron-60 is made by only one thing in nature — a supernova," said Benitez.
"A supernova sprays space with many different elements. Many are rare — like iron-60. These particles hit our atmosphere and settle like a thin layer of dust over the planet."
Intriguingly, the iron-60 layer found by the German group did not come from a single supernova but appeared to come from a number of them. "Different layers seem to have fallen at different times, but all around two million years ago," said Benitez.
In addition, observations of space around our sun have revealed that unlike the rest of the galaxy, space near us has little interstellar gas in it. "Essentially it is missing much of its dust and gas — just as if a supernova had cleaned it out," added Maiz-Apellaniz.
In other words, our tiny corner of the galaxy appears to have been swept clean by a supernova brush about two million years ago. Intriguingly, at just this time, a set of extinctions — known as the Pliocene/Pleistocene extinctions — is also known to have occurred.
Geologists have found that plankton and molluscs were wiped out in vast numbers and that land animals and plants were also affected. "We now think these creatures were killed off because earth’s ozone was blasted away by two or more supernovae," said Benitez.
"There would have been no protection against the sun’s intense ultraviolet radiation. All sorts of changes could have resulted."
It was also around this time that mankind’s direct ancestor, Homo erectus, the species considered to be the first true human being, appeared in Africa and Asia after replacing more primitive ape-like creatures such as Australopithecus africanus. These beings may have been some of the lucky few who were able to advantage of conditions in these hazardous, radioactive times. This triumph only occurred thanks to this celestial intervention, however.
"It is a very interesting idea," said Prof Chris Stringer, of the Natural History Museum in London. Certainly, quite a number of extinctions around this period. At the same time, Homo erectus was beginning to make its way in the world.
"However, we would have to tie
down the datings of the supernovae eruptions and also the dates that
the layers of the iron-60 were deposited before we could be really
sure if we got a bit of evolutionary help from above or not." —
NEW PRODUCTS & DISCOVERIES
IN her hit movie "Speed", Sandra Bullock drove a bus with a mind of its own, programmed to explode if it went below 50 m.p.h. Now buses on real-life autopilot are coming to Las Vegas.
A camera mounted on the dashboard of the electric-powered Civis reads stripes painted on the road. If a bus strays even slightly from the markings, a motor on the steering wheel nudges the bus back in line. Human drivers, who control the brakes and accelerator, play only a bit part in this action flick. Availability: October, 2003
To learn more: www.irisbus.com
"Smart fluid" developed
"Smart Fluid", a liquid polymer, which gets solidified in the presence of a magnetic field and changes back into liquid within seconds after the magnet is removed, has been developed by a scientist of the National Physical Oceanography Laboratory (NPOL) in Kochi.
The "smart Fluid" has many applications, including for making automobile brakes, clutches, moulds, vibration damping, tunable elastomers and safety valves, Dr Reji John, who developed the fluid, and has exhibited it at the ongoing ‘Swadeshi Vijnana’ mela told PTI.
Dr John said the presence of the magnetic field builds up the viscosity in the fluid. The initial viscosity of the fluid is around 500 CPS (Cetri Poise). If magnetic field of one gauss is applied, viscosity becomes 1.5 lakh CPS within 0.2 sec and as soon as the magnetic field is removed, it touches its initial viscosity of 500 CPS immediately, he said.
Dr John said the fluid, called ‘Magnetorheological’ was developed by him six months ago and can have wide defence applications. The institute has applied for patenting in US, UK, France, Japan, besides India, he said. PTI
Speak to it and hear it translate
A Russian company has developed a pocket-sized gadget that can translate spoken English into French, German or Spanish.
Aimed at the frequent traveller, the user just has to say a phrase in English instead of thumbing through a dictionary and the device translates it and then repeats out loud in the foreign language in a robotic voice.
According to Arkady Davydov of Ectaco which developed the product, this is the first translator in the world that understands voice. "It is more than an electronic phrasebook because it recognises any phrase you say. "In the future we will have models for all the other languages," he was quoted by BBC saying.
The next steps are adding more languages, including English to Chinese by the end of the year. "Two speakers, English and Chinese, will be able to communicate live without having to use the phrasebook or dictionary," said Davydov. "It is going to be really amazing." Accurate 90% of the time, The Universal Translator UT-103 was developed by the Ectaco company based in St Petersburg, Russia.
The device fits in a pocket with ease. It uses AA batteries and costs $ 249.95, which could pay for a few bulky paper dictionaries.
The specially-developed speech recognition software allows it to recognise and translate 3,000 phrases commonly used in all kinds of travel. They include categories such as eating, shopping and driving.
Specialists using Ectaco say the translator will understand what you say, regardless of your accent. Developing the device, they recorded more than 700 native English and foreign speakers to create a phonetic bank of all recorded phrases. ANI
Novel plastics films
To minimise the risk of active agents that kill microorganisms from being washed out and posing a risk to human health, researchers have successfully treated plastics with chemicals which bind the agents more firmly.
Microorganisms can be extremely helpful — cleaning up effluent and contaminated soil, giving the desired flavour to foodstuffs such as cheese, yogurt and wine, producing essential vitamins in human bodies and manufacturing drugs such as insulin and antibiotics in industrial fermenters.
But most people become aware of their presence when they multiply out of proportion causing outbreaks of disease, spoiling food or causing wood to rot.
However, the active agents utilised to kill microorganisms often pose a risk to human health. The biocides also have another disadvantage that over time, they are washed out and lose their effectiveness, a report in Fraunhofer Gesellschaft said.
With the solution demanding a more
firm binding of these biocides to the material being treated,
scientists at the Fraunhofer Alliance for Polymer Surface, POLO, have
developed a new technique of using relatively innocuous polyammonium
compounds and natural agents and coupling them chemically to the
surface of plastic materials. PTI
SCIENCE & TECHNOLOGY CROSSWORD
1. A measure of purity of gold.
5. Glass-like substance produced during extraction of metals.
8. A white powder insoluble in water and used to extract alu- minium.
10. Short for coarse aggregate.
11. Warships operating under- water surface.
13. Farthest known planet.
14. Abbr. for national highway.
16. India’s famous public under taking dealing with coal.
17. International Energy Agency (abbr.)
19. Short for unit for pressure.
20. A projection from a frame for fixing purposes.
22. The control electrode in a transistor.
24. A unit of current.
27. Scientist whose theory said all elements were made of hydrogen atoms.
28. Symbol for lead.
1. An oil used in paint and varnish industry and as a laxative too.
2. Most abundant metal on earth’s crust.
3. A red form of corrundum.
4. A colourless gas having pungent smell.
5. A steel producing giant of India.
6. Acid contained in vinegar.
7. An internal combustion engine fuel.
9. Highest honour bestowed by UGC upon national scholars. (abbr.)
12. Energy needed to be used for peaceful purposes.
15. Used for different forms.
18. Abbr. for Ante Meridiem.
20. Provided in steel reinforcement.
21. Abbr. for Geraniol Pyrophosphate.
23. Moisture of a freshly quarried stone.
25. Short for engineer.
26. Symbol for a soft silvery metal lic element.
Solution to last week’s