earths magnetic field, also known as the geomagnetic field
They changed over time by finding the right ingredients such as iron, metal, or steel to forge different creations. They took so slowly because no one was discovered the things to make stone tools.
I believe the answer is: Primary
For example, let's say take a look at normal employees at a company.
For most of them, the main reason they spend their time to do the job correctly is to obtain money/salary even though they have to spend their time being scolded by unlikable boss.
In the scenario above, we can say that money is the primary reinforcer for the target behavior
Refuse to obey laws that are unfair and unjust to all citizens
