Listening. Natural selections: climate and carbon dating

NATURAL SELECTIONS: CLIMATE AND CARBON DATING

1. What do you know about application of nuclides? What isotopes are usually used and for what purposes?

2. Read the passage about carbon dating and fill in the gaps with words and expressions below:

Radiocarbon dating, or carbon dating, is a …………………. method that uses the naturally occurring …………….. carbon-14 (¹⁴C) to determine the age of carbonaceous materials up to about 60,000 years.

One of the most frequent uses of radiocarbon dating is to estimate the age of organic remains from archaeological sites. When plants fix atmospheric …………….......... into organic material during photosynthesis they incorporate a quantity of ¹⁴C that approximately matches the level of this isotope in the atmosphere (a small difference occurs because of isotope fractionation, but this is corrected after laboratory analysis). After plants die or they are consumed by other organisms (for example, by humans or other animals) the ¹⁴C fraction of this organic material declines at a fixed ………………… due to the radioactive decay of ¹⁴C. Comparing the remaining ¹⁴C fraction of a sample to that expected from atmospheric ¹⁴C allows the age of the ………………. to be estimated.

The technique of radiocarbon dating was ……………………… by Willard Libby and his colleagues at the University of Chicago in 1949. Emilio Segrè asserted in his autobiography that Enrico Fermi suggested the concept to Libby in a seminar at Chicago that year. Libby estimated that the steady state radioactivity concentration of exchangeable carbon-14 would be about 14 …………………. per minute per gram. In 1960, he was awarded the Nobel Prize in chemistry for this work. He first demonstrated the ……………………of radiocarbon dating by accurately measuring the age of wood from an ancient Egyptian royal barge whose age was known from historical documents.

3. You are going to listen to a part of a radio program ‘The Chemical Reporter’ about radiocarbon dating. You will come across the following expressions:

commonly occurring compound, carbohydrates, carbon cycle, with a great deal of accuracy, pioneer of the method, C stands for ‘carbon’, in constant and predictable proportions, a minute fraction, retain 14 nucleons forever, not to feel the tooth of time, to give off radiation,

4. Listen to the talk for the first time and make notes on the following points:

- carbon cycle

- isotopes of carbon

- basics of carbon dating method

5. When listening for the second time, fill in the gaps with missing information (a maximum of 3 words):

1. In the air the element can be found in a commonly occurring compound ………………….

2. All of these steps together make up the………………...

3. And even thousands of years later, that moment can be dated using the ……………………….

4. The nucleus in a typical carbon atom is made up of 12 particles known as ……………… and the chemical code used to describe it is ¹²C………..

5. These three ……………….. can be found on our planet in constant and predictable proportions.

6. The¹⁴C atoms have something ………………….: the do not retain 14 nucleons forever.

7. ¹²C and ¹³C are stable, they do not feel the tooth of time but carbon-14 …………… over the centuries

8. The rest have given off radiation and reverted to …………….. ¹³C and ¹²C forms of the atom.

9. In other words, carbon-14 is radioactive, hence the name …………………

10. By counting how many ¹⁴C atoms are left in a piece of ………………. you can therefore ………………..

SECTION 3