Isotherms cannot cross because to cross would indicate two different temperature for the same location.
Isotherms are lines that connect points of equal temperature on weather maps, so at every point along a given isotherm the temperature values are the same.
An isotherm should never split, cross, or touch another isotherm, because then at the crossing point it would have two different temperature values, which is physically impossible.
Biogeochemical cycles represent the main system by which the energy of the Sun is transformed into energy of the chemical compounds by living beings and products of their activity. :)
