The paper considers the two-century-old problem of how solar spots influence biological objects on the Earth. It describes the modern state of the kT-problem, which for a long time has been the most difficult obstacle in explaining solar activity effects. Based on recent advances in spin chemistry and magnetoplasticity physics, it is shown that a ‘molecular target’ sensitive to weak electromagnetic fields is spins in non-equilibrial states of the molecular system. A way of how solar spots can influence Earth's molecular, including biological, processes through a ‘transparency window’ in the Earth's atmosphere is proposed.
