So the amount of carbon 14 in the atmosphere hasn't or can't be changed?

The amount of Carbon-14 (C-14) in the atmosphere has not remained constant over time. It is continuously produced in the atmosphere through the interaction of cosmic rays with nitrogen-14. However, the concentration of C-14 in the atmosphere can vary due to factors such as changes in solar activity, the Earth's magnetic field, and human activities.

1. Cosmic rays: High-energy particles from space constantly bombard the Earth's atmosphere. These particles interact with nitrogen-14 atoms, converting them into C-14.

2. Solar activity and Earth's magnetic field: The sun's activity and the Earth's magnetic field can influence the rate at which cosmic rays reach the Earth's atmosphere, and thus the rate of C-14 production.

3. Human activities: Activities such as the burning of fossil fuels and nuclear testing can also affect the amount of C-14 in the atmosphere. Fossil fuels contain almost no C-14, so burning them dilutes the atmospheric C-14 concentration. Nuclear testing, on the other hand, can increase the amount of C-14 in the atmosphere.

So, the amount of C-14 in the atmosphere can and has changed over time due to both natural and human factors.