Food for thought:
I assume over the past 100y measurements got very precise hence the accurate dotted line downwards.
Now what if the field gets more intense again over the next 100y.
Now let’s sa...
They derive the old data points in a number of ways. Ancient pottery contains magnetic particles that realign with earth's magnetic field after kilning for example.
Ancient tree rings do a similar thing with minerals they accumulate and deposit.
Ash from forest fires and volcanism lay down soil layers do a similar thing as they cool.
Ancient tree rings do a similar thing with minerals they accumulate and deposit.
Ash from forest fires and volcanism lay down soil layers do a similar thing as they cool.