And click on the Time Machine icon. Click on âSelect Diskâ. Choose your external drive and click on âUse Backup Diskâ. Time Machine will copy everything (OS, Software, Files, and Preferences) to the external hard drive.
The standard enthalpy of formation of a pure element is in its reference form its standard enthalpy formation is zero. Carbon naturally exists as graphite and diamond. The enthalpy difference between graphite and diamond is too large for both to have a standard enthalpy of formation of zero. To determine which form is zero, the more stable form of carbon is chosen. This is also the form with the lowest enthalpy, so graphite has a standard enthalpy of formation equal to zero. Table 1 provides sample values of standard enthalpies of formation of various compounds.
Upon death, Carbon 14 in the decomposing body undergoes its own decomposition or radioactive decay which is what radioactive carbon dating measures. Carbon 14 (affectionately called C14) is not a stable isotope of Carbon and has to decay into the much stabler Nitrogen 17 (which can be found in the atmosphere). Therefore, once an organism dies, the C14 it holds in its body wriggles free in a radioactive decay process. The half-life of C14 is 5, 730 years and thus makes a pretty accurate factor for dating fossils which can be billions of years old.