2020ApJ...904..137T

Recent knowledge of Galactic dynamics suggests that stars radially move on the disk when they encounter transient spiral arms that are naturally generated during the process of disk formation. We argue that the large movement of the solar system from the innermost disk over its lifetime is inferred from an elemental abundance pattern of the Sun to those of solar twins within the Galactic chemical evolutionary framework. The implied metal-rich environment at the Sun's birthplace and its formation time are supported by measured silicon isotopic ratios in presolar silicon carbide grains. We perform numerical simulations of the dynamical evolution of disk stars in a Milky Way-like galaxy to identify the lifetime trajectory of the solar system. We find that a solar system born in the proximity of the Galactic bulge could travel to the current locus by the effect of radial migration induced by several major encounters with spiral arms. The frequent feature we identify is the repeated passages of stars inside the same spiral arm owing to the wobble of stars traveling in and out of the spiral arms. We predict that such episodes are evidenced in the Earth's geological history as snowball Earth and that their occurrence times are within our predictions. In particular, the stellar motion that vertically oscillates during passages through spiral arms occasionally leads to a split into two discrete passage episodes with an interval of several tens of megayears, implying two relevant snowball Earth events that occurred in rapid succession (∼720 and 650 million years ago).