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The most incomprehensible thing about the world is that it is at all comprehensible. - Albert Einstein
Not only does God play dice, but... he sometimes throws them where they cannot be seen. - Stephen Hawking
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Atoms which differ only in the number of neutrons are called isotopes. Carbon has three isotopes:
Radiocarbon dating is based on the 14C isotope. It is one of the most widely-used dating method and used to determine how long ago once-living material died. This method was developed in the 1950's by Libby who won a Nobel prize for this work. 12C and 13C are stable and nonradioactive isotopes. Whereas, 14C is unstable isotope with a half-life of 5730 years. Where half-life is the time interval required for a quantity to decay to half of its initial value. Chemistry of carbon dating 1. 146C is produced in the upper atmosphere from the bombardment of Nitrogen by neutrons (cosmic rays) 147N + neutron ---> 146C + proton 2. 146C reacts with oxygen and produce carbon dioxide and mixed in the atmosphere. 146C + 02 ---> 146C02 3. 146C02 enters the food chain through the process of photosynthesis. Now, plants are radioactive and animals that eat plants are also radioactive. It is assumed that the 146C/136C/126C ratios in tissue are the same as in the atmosphere. Note that in photosynthesis all three carbon isotopes are participating, of course, in different amount. 4. When an organism dies it stops consuming CO2 so the up-take of carbon ceases. At this stage the ratio between the three carbon isotopes 146C/136C/126C changes because the unstable isotope 146C changes. The decay of radioactive isotopes is a time-dependent negative exponential function. Thus death sets the radiometric "clock" to measure how long ago once-living material died |
Points “A”, “B”, “C” and “D” are placed on a circle such that they form a quadrilateral of maximum area for the given circle. The line “AC”, a diagonal of []ABCD, passes through the center of the circle. Find the ratio of the area of the circle to the area of the quadrilateral []ABCD. |
Everything changes. Stars are born from stellar dust. They evolve and reach peak of their adulthood. They decay and eventually die. Planets change their positions. Seasons come and go. Leaves turn their colors and so on. We study these changes. How do we study a change if everything else is also changing? How do we quantify a change with respect to a changing background? What do we quantify in a change? |
