Where Grey Matter meets Dark Matter
Episode 30 - 26 March 2011
A big meteorite smashed into the earth; huge tsunamis roiling across the oceans and inundating the land; hadean conflagrations wholly obliterated any organic material within reach of their oxidizing tendrils. Overall, the dinosaurs had a pretty uncomfortable time. (They were also out of coffee.)
Source: Nasa Images.
No-one's really sure what exactly killed the dinosaurs about 65 million years ago, but it looks like it might have been a combination of all these things.
How do we know there was an asteroid impact? All around the world you can find a thin layer (a few centimetres thick) of dirt which contains a huge amount of information. Below the layer (ie, in the older rock) we have dinosaurs, and above it we have no dinosaurs (more or less). In the layer we find a large amount of iridium. There's not that much iridium in Earth's soil, but there does tend to be a lot on asteroids, so we think that this was probably caused by a huge asteroid impact. Add to that the big crater in Mexico which dates to about 65 million years ago, and it's starting to add up.
A bit of the KT boundary from Wyoming, USA.
Source: San Diego Natural History Museum.
How do we know there were huge tsunamis? If a giant asteroid slams into the earth, there's going to be tsunamis from the shockwave.
How do we know there was heaps of fires? Also in the thin layer we have a large amount of soot, and it doesn't take too much imagination to infer that there were huge fires around the world to create all that soot.
How do we know that the dinosaurs were out of coffee? Coffee (probably) hadn't evolved yet.
- Here's a bunch of academic references:
-Belcher C. M., Collinson M. E. & Scott A. C. 2005. constraints on the thermal energy released from the Chicxulub impactor: new evidence from multi-method charcoal analysis. Journal of the Geological Society, London 162, 591-602.
-Belcher C. M., Collinson M. E., Sweet A. R., Hildebrand A. R. & Scott A. C. 2003. Fireball passes and nothing burns – the role of thermal radiation in the Cretaceous-Tertiary event: evidence from the charcoal record of North America. Geology 31, 1061-1064.
-Melosh H. J. 1990. Reentry of fast ejecta: The global effects of large impacts. Transactions of the American Geophysical Union 71, 1429.
-Robertson D. S., McKenna M. C., Toon O. B., Hope S. & Lillegraven J. A. 2004. Survival in the first hours of the Cenozoic. Geological Society of America Bulletin May/June.
Tron - a story about computers (and people) gone bad. It also has lightcycles. The film required a huge amount of computing to produce, but believe it or not, computers (and their graphical displays) are even better now than they were in 1982. And, computers are no longer the province of the geeks and science fiction writers, everybody has one.
Since they're everywhere, We all know how computers work; you attach the metal rope to the spark box on the wall, and strike the button that dynamizes the electrons. But what exactly do the computers do with these electrons? To answer that we need to know what the inside of a computer is made of.
Anybody with a passing interest in avoiding electrocution has a basic understanding of conductors (like iron, silver and other metals) and insulators (like dry wood and rubber). You shouldn't stick the former in the toaster, meaning that conductors allow electricity to flow easily, while insulators don't. The difference between them is how easy it is get the electrons separated from their atoms. The standard way to think about this is in terms of energy levels.
All the lowest energy levels in a solid are filled by the electrons tightly bound to the atom (the electrons with the lowest energy, which are closest to the atom), or used for bonding the solid together; we call these bonding electrons the 'valence' electrons. The electrons with the highest energy are not so tightly bound and if they can jump up an energy level or two, then they are free of their bondage and can take part in the great enterprise of electricity conduction. The energy for the electrons to jump up comes from thermal agitation; ie. as a solid warms up the electrons become more energetic. This is a common principle among all materials; the difference between conductors and insulators is how much energy the electrons need to jump up to conducting energy levels (which we call the conduction band).
For a conductor, the conduction band begins right at the top of the valence band and so the electrons only need a tiny bit of energy to become conduction electrons.
The energy levels in the valence band and the conduction band are right next to each other in a conductor.
But for insulators, the conduction band is separated from the valence band by a much bigger gap, and so the electrons in the valence band are bound in perpetual vassalage.
In between these situations though, we have semi-conductors, where there is still a gap, but it's a small gap. This means that some of the electrons will have enough energy to jump up and conduct electricity.
But the conduction band is only slightly above the conduction band in a semi-conductor.
In order to increase the number of conduction electrons, you can add 'dopant' molecules to the semi-conductor, which bring with them extra electrons, or extra 'holes' in which to put electrons.
These semi-conductors are handy because they only conduct a small amount of electricity, and you can control the amount that is being conducted. Now this is just what you want in computers. Remember that the basis of computer information is the bit, ie. a '1' or a '0'. Now if you can build and control a device that conducts sometimes, and not at other times then you can assign the number '1' to the state when current is flowing and the number '0' to when current isn't flowing (or vice-versa). And that's where we get into the realm of transistors and actually building a computer. We'll pick up on this next time.
- Halliday, D., Resnick, R. & Walker, J. (1997), Fundamentals of physics: 5th edition, John Wiley & Sons , New York.