After two half-lives, another half of your leftover Carbon-14 would have decayed into Nitrogen-14.
Half of 50% is 25%, so you would have 25% Carbon-14 and 75% Nitrogen-14.
In a related article on geologic ages (Ages), we presented a chart with the various geologic eras and their ages.
In a separate article (Radiometric dating), we sketched in some technical detail how these dates are calculated using radiometric dating techniques.
One way that helps scientists place fossils into the correct era on the Geologic Time Scale is by using radiometric dating.
The overall reliability of radiometric dating was addressed in some detail in a recent book by Brent Dalrymple, a premier expert in the field. 80-81]: These methods provide valid age data in most instances, although there is a small percentage of instances in which even these generally reliable methods yield incorrect results.
147] has highlighted the fact that measurements of specimens from a 1801 lava flow near a volcano in Hualalai, Hawaii gave apparent ages (using the Potassium-Argon method) ranging from 160 million to 2.96 billion years, citing a 1968 study [Funkhouser1968].
In the particular case that Morris highlighted, the lava flow was unusual because it included numerous xenoliths (typically consisting of olivine, an iron-magnesium silicate material) that are foreign to the lava, having been carried from deep within the earth but not completely melted in the lava.
You would need to have access to scientific instruments at this point that could measure the amount of radioactivity in the sample, so off to the lab we go!
After you prepare your sample and put it into the machine, your readout says you have approximately 75% Nitrogen-14 and 25% Carbon-14.