Natural processes absorb the equivalent of all natural emissions plus about 57% of man-made emissions, leaving an additional 16 billion metric tons of CO2 in the atmosphere each year. † In permafrost regions, perennial snow accumulations trap air bubbles that leave records of past airborne CO2 concentrations,   and because regional CO2 concentrations vary by less than 10 parts per million over the Earth, these local records are globally representative.  * Instruments located on satellites can measure certain properties of oxygen that vary with temperature.
However, "relative" dating or time can be an easy concept for students to learn.
The Muslims count the Prophet’s departure from Mecca, or the Hegira, as their beginning at AD 662.
The Mayan calendar used 3114 BC as their reference.
Its density fluctuates from 2.25 g/cm³ (1.30 ounces/in³) for graphite and 3.51 g/cm³ (2.03 ounces/in³) for diamond.
The melting point of graphite is 3500ºC (6332ºF) and the extrapolated boiling point is 4830ºC (8726ºF).