Thomas’s ‘process’ poetry draws attention to the physical matter from which humans are formed and to which we return, and to the constant recycling of that matter into other life forms in an ongoing cycle of creation and destruction across what we now understand as deep time. It obsessively investigates the place of the human in this epochal time frame: an animal both part of and apart from this ongoing cycle. My paper will introduce this concept through a close reading of ‘The force that through the green fuse’ before turning to the manifestation of this obsession in late work informed by Thomas’s fears of nuclear holocaust. In particular, it will show how ‘In Country Sleep’ (1947), ‘Over Sir John’s hill’ (1949), and ‘Poem on his Birthday’ (1952) are haunted by landscapes of future atomic war: ‘the deep dark zero’ and ‘the cyclone of silence’ that would follow nuclear holocaust. His engagement with these imagined sites of future contamination necessitate a re-engagement with the assumptions about deep and cyclical time that govern the earlier ‘process’ poetry. I will suggest that Thomas’s late poetry offers us with new ways to situate ourselves within the complexities of the current crises of climate and apocalypse.