TOEFL Listening Practice: Lecture02
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MP3 – SoundCloud
Answer
- D
- A
- C
- A, C
- B
- B
Transcript
| Professor: | In this lecture, we’re going to look at the Iron Age, and, in particular, what caused it. And it wasn’t simply a chance discovery of a metal that turned out to be better than previous ones. The age that preceded the Iron Age was the Bronze age. Bronze is an alloy of copper and tin. But it’s not true to say that during the Bronze age, people didn’t have iron. Smelted iron objects go back as far as 3000 BC: they’ve been found throughout ancient Mesopotamia, Anatolia, and Egypt, including an iron sword that dates back to circa 2800 BC. It wasn’t until 1600 to 1200 BC that iron began to be used as a working metal, but even then bronze was still dominant, so we don’t consider the Iron Age to really have started until the end of that period. Of course, Iron Age is not a terribly helpful term anyway, in terms of chronology, as different places on earth began to adopt it at different times. |
| Iron, at first, was considered rare and expensive. Gifts of iron artifacts were given to other rulers, but it was probably considered inferior to bronze because, as wrought iron, it would not hold an edge. So, how did it all come about? Well, as with most discoveries, we assume that it occurred by accident. But how? There are a number of theories. One is that iron was discovered by the Egyptians when they melted gold. The Nubian gold dust from which they got their gold was rich in magnetite, which could have produced small quantities of iron during the process. However, since iron is 50% soluble in gold at gold’s melting point, very little iron would have been separated from the gold, so that theory seems unlikely, although it would account for its value. An older theory suggests that iron ore may have been used by mistake instead of copper ore when producing copper or bronze. But that theory doesn’t hold water, as iron ore was relatively abundant, and a smelter that could create a valuable material by mistake would carry on doing so. A more accepted theory is that iron ore could have been used as a flux, to encourage the copper to melt. Depending on the temperature, the amount of oxygen present, the iron content of a particular flux, and the quantity of flux, the production of iron would have seemed to be completely random event, and the smelter would not be able to reliably repeat the process. That, therefore, would account for both the value and the scarcity of iron at the time. | |
| It doesn’t, however, explain why iron eventually came to replace bronze. Iron is no better than bronze as a tool or weapon. It’s only when the metalworker dissolves carbon in the iron – a process we call carburization – and he quenches – that is, wets the resulting metal – we get steel, then we see a definite advantage of iron over bronze. The discovery of iron carburization goes back to around 1200 BC, which coincides with the time that iron took off as the preferred metal. Its discovery was almost certainly an accident, as it’s nothing like the way bronze was worked, and the discoverer probably wasn’t sure, first time around, what he had done to create the new metal. But, because we see many iron implements as well as carburized iron implements around that time, there needed to be something else, some other reason why iron started to be used instead of bronze. Some believe that the reason was a shortage of bronze. There is some evidence of this, as bronze items dating back to this era were remelted and reused. | |
| What caused the shortage? Well, as I mentioned before, bronze is made from copper and tin. Let’s consider copper first. The big producer of copper at that time was Cyprus, and there is evidence that Cyprus stopped exporting copper around 1200 BC, at least for a little while. But Cyprus still had its own supply of bronze, so it could have manufactured bronze implements, even if it wasn’t exporting them. But that doesn’t seem to be the case. Cyprus adopted iron at the same time as other countries and was also recycling bronze at home, suggesting that it was a shortage of tin, not copper, that halted production. At the time, tin was probably imported from beyond the Near East, via Iran. Political disruption in these quarters may have affected the existing tin trade routes and forced people to consider iron as an alternative, despite it being cheaper and less effective. Of course, after the discovery of carburization and quenching, steel was both cheaper and more effective than bronze, and that’s when we see the iron age really accelerate |