primary issue explored here is the survival of the hydrosphere. The magnetic field acts to prevent atmospheric erosion by the solar wind. In the case of the early Earth, the magnetic field would have had to balance the greatly enhanced solar wind pressure associated with the young rapidly-rotating Sun. The interplay between the magnetic field and radiation from the young Sun controls the loss of light elements and, ultimately, water and therefore may be a fundamental stage in the development of a habitable planet.

The interaction of the solar wind and the geomagnetic field produces Earth’s magnetosphere (Figure 1), with the magnetopause ($r_{s}$) defined as the point toward the Sun (the sub-solar point) where the wind pressure is balanced by the magnetic field [@Griessmeier2004]:\
$$r_s=\left[\frac{\mu_0f_0^2M_E^2}{4\pi^2(2\mu_0n_{sw}m_{p}v_{sw}^2+B^2_{IMF})}\right]^{1/6}$$\
where $M_{E}$ is Earth’s dipole moment, $n_{sw}$ is solar wind density, $v_{sw}$ is solar wind velocity, $f_{0}$ is a magnetospheric form factor (=1.16 for Earth), $\mu_{0}$ is the permeability of free space, $m_{p}$ is a proton mass and $B_{IMF}$ is the interplanetary magnetic field.

Today, Earth’s magnetic field stands off the solar wind to a distance between 10 and 11 Earth radii. The occurrence of magnetic storms and their associated phenomena– including auroral lights seen 