TPO 15 Lecture 3 Art History
Narrator:
Listen to part of a lecture in an art history class.
Professor:
Now in Europe in the Middle Ages before the invention of printing and the p r inting pres s, all books, all manual scripts were hand-made. And the material typically used for the pages was parchment, which is animal skin that stretched and dried under tension, so it bec o me s really fat and can be written on. During the 1400s, when printing was being developed, paper became the predominant material for books in Europe, but prior to t hat, it was parchment. Parchment is durable, much more so than paper, and it could be reus ed which came in handy since it was a costly material and in short supply. So it wasn ' t uncommon for the scribes or monks who produce the manual scripts. Ah, remember before printing books were made mainly in monasteries. Well, the scribes often recycled the parchment that ' d been used for earlier manual scripts. They simply erased the ink off the parchment and wrote something new in its place A manual script page that was written on, erased and then used again is called a palimpsest. Palimpsests were created, well, w e kn ow about two methods that were used for removing ink from parchment. In the late Middle Ages, it was customary to scrape away the surface of the parchment with an abrasive, which completely wiped out any writing that was there. But earlier in the Middle Ages, the original ink was usually removed by washing the used parchment with milk. That removed the ink. But with the passing of time, the original writing might reappear. In fact , it might rea pp ear to the extent that scholars could make out an even deci p her , the original text. Perhaps, the most famous example is the Archimedes' palimpsest.
Archimedes li v e d in G re ece around 200 BCE, and as you probably know, he's considered one of the greatest Mathematicians who ever lived, even though , many of his writings had been lost , includi ng what many now think to be his most important work called The Method. But in 1998, a book of prayers from the Middle Ages sold in an art auction for a lot of money, more money than anyone would pay for a damaged book from the 12th century. Beautiful or not, why? It had been discovered that the book was a palimpsest, and beneath the surface writing on the manual script laid, guess what? Mathematical theorems and diagrams from Archimedes.
Archimedes' writings were originally done on papyrus scrolls. Then in the 10 th century, a scribe made a copy on parchment of some of his texts and diagrams including, as it turns out, The Method. This was extremely fortunate, since later on, the original papyrus scrolls disappeared. About 200 years later in the 12 th century, this parchment manual script became a palimpsest when a scribe used the parchment to make a prayer book.
So the pages, the pieces of parchment themselves, had been preserved.
But the Archimedes' text was erased and written over, and no one knew it existed. It wasn't until 1906 that a scholar came across the prayer book in a library and realized it was a palimpsest, and that the underlying layer of texts could only have come from Archimedes. That was when his work The Method was discovered for the first time.
Um... the palimpsest then went through some more tough times, but eventually it ended up in an art auction where was bought and then donated to an art museum in Baltimore, for conservation and study. To avoid further damage to the manual script, the research team at the art museum has had to be extremely selective in their techniques they used to see the original writing. They've used ultraviolet light and some other techniques, and if you're interested in that sort of thing, you can learn more about it in an art conservation class. But act ually, it was a physicist who came up with a method that was a breakthrough. He realized that the iron in the ancient ink would display if exposed to a certain X-ray imaging method, and except for small portions of the text that couldn't be deciphered, this technique's been very helpful in seeing Archimedes' texts and drawings through the medieval over w riting.
TPO 15 Lecture 4 Biology
Narrator:
Listen to part of a lecture in a biology class.
Professor: OK. We've been talking till now about the two basic needs of a biological community – an energy source to produce organic materials, you know ah, food for the organism，and the waste recycling or breakdown of materials back into inorganic molecules, and abo ut how all this requires photosynthesis when green plants or microbes convert sunlight into energy and also requires microorganisms, bacteria, to secrete chemicals that break down or r ecycle the organic material to complete the cycle So, now we are done with this chapter of the textbook, we can just review for the weekly quiz and move on to the next chapter, right? Well, not so fas t. First, I ‘d like to talk about some discoveries that have challenged one of these fundamental assumptions about what you need in order to have a biological community.
And, well, there actually were quite a few surpris es. I t all began in 1977 with the exploration of hydrothermal vents on the ocean floor.
Hydrothermal vents are cracks in the Earth's surface that occur, well, the ones we are taiking about here are found deep at the bottom of the ocean. And these vents on the ocean floo r, they release this incredibly hot water, 3-4 times the temperature that you boil water at be cause this water has been heated deep within the Earth. Well about 30 years ago, researche rs sent a deep-sea vessel to explore the ocean's depth, about 3 kilometers down, way deep to ocean floor, No one had ever explored that far down before. Nobody exp ected there to be any life down there because of the conditions. First of all, sunlight doesn't rea ch that far down so it's totally dark. There couldn't be any plant or animal life since there's no sunlight, no source of energy to make food. If there was any life at all, it'd just be some bacter ia breaking down any dead materials that might have fallen to the bottom of the ocean.And?
Student 1
And what about the water pressure? D idn't we talk before about how the deeper down into the ocean you go, the greater the pressure?
Professor
Excellent point! And not only the extreme pressure, but also the extreme temperature of the water around these vents. If the lack of sunlight didn't rule out the existence of a biological community down there then these factors certainly would, or so they thought.
Student 2
So you are telling us they did find organisms that could live under those conditions?
Professor: They did indeed, something like 300 different species Student 1 But... but how could that be? I mean without sunlight, no energy, no no …
Professor:
What they discovered was that microorganisms, bacteria, had taken over both functions of the biological community - the recycling of waste materials and the production of energy. They were the energy source.
You see, it turns out that certain microorganisms are chemosynthetic - they don't need sunlight because they take their energy from chemical reactions
So, as I said, unlike green plants which are photosynthetic and their energy from sunlight, these bacteria that they found at the ocean floor, these are chemosynthetic, which means that they get their energy from chemical reactions. How does this work?
As we said, these hydrothermal vents are releasing into the ocean depth this intensely hot water and here is the thing, this hot water co ntains a chemical called hydrogen sulfide, and also a gas，carbon dioxide. Now these bacteria actually combine the hydrogen sulfide with the carbon dioxide and this chemical reaction is what produces organic material which is the food for larger organisms. The researchers had n ever seen anything like it before.
Student 2：
Wow! So just add a chemical to a gas, and bingo, you've got a food supply?
Professor
Not just t h at! W hat was even more surprising were all the large organisms that lived down there. The most distinctive of these was something called the tube worm. H ere, let me show you a picture.
The tube of the tube worm is really, really long. They can be up to one and half meters long，and these tubes are attached to the ocean floor, pretty weird looking, huh?
And another thing, the tube worm has no. mouth, or digestive organs. So you are asking how does it eat? Well, they have these special organs that collect the hydrogen sulfide and carbon dioxide and then transfer it to another organ, where billions of bacteria live. These bacteria that live inside the tube worms, the tube worms provide them with hydrogen sulfide and carbon dioxide. And the bacteria, well the bacteria kind of feed the tube worms through chemosynthesis, remember, that chemical reaction I described earlier.
