The age of the ND group and that of the SU-WU group are distinguishable from the latest age estimate of the Laschamp excursion.Overall, these age data from volcanic rocks show that at least three excursions occurred between approximately 30 and 60 ka.
Without this knowledge, he argued that, "As for the future, we may say, with equal certainty, that inhabitants of the Earth cannot continue to enjoy the light and heat essential to their life, for many million years longer, unless sources now unknown to us are prepared in the great storehouse of creation."The same is true of the basis of Kelvin's estimate of the age of the Earth.
In the present study, we have carried out further K-Ar age determinations on three other volcanoes and obtained reliable ages for two of them: 30±5 ka for the Puketutu volcano of the ND group and 50±6 ka for the Mc Lennan Hills volcano of the SU group.
The age of Puketutu agrees well with that of Wiri, and these two ages give a weighted mean age of 29±3 (1σ) ka for the ND group.
These three excursions are likely to be confined in the weak dipole interval of 20–70 ka, and all of these excursions yield particularly low virtual dipole moments (VDMs) of 2×10 or less.
Since it is suggested that the larger virtual geomagnetic pole (VGP) deviations from the geographic pole are related to the lower VDMs, the excursional fields possibly have resulted from a significantly reduced dipole field and comparable non-dipole components.© The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences.