The geological record also doesn't show much evidence for
major changes in the intensity of the ancient
magnetic field over the past 4 billion years.
Renown solar scientist Dr. K.G. McCracken from the Institute for Physical Science and Technology, University of Maryland,
in 2007 published paper:
Changes in the cosmic ray and heliomagnetic components of space climate, 1428 — 2005, including the variable occurrence of solar energetic particle events McCracken 2007 paper
Major result of McCracken investigation based on 10Be dating is: the estimated annual average heliospheric
magnetic field strength near Earth, 1428 — 2005, based on the inter-calibrated cosmic ray record as shown
in Fig. 2 on p. 1073 (4 of 8).