Evidence that Earth was exposed to Cold Dense Interstellar Medium 2 Myrs Ago as a result of the Encounter with Local Lynx Cold Clouds

Abstract The relationship between the location of the Sun in the interstellar medium (ISM) and terrestrial effects has been explored in connection with the filtration of Galactic Cosmic Rays (GCR) as the heliosphere, the solar system’s protective bubble formed by the solar wind, shrinks or expands as a result of different ISM environments. The connection between GCR and terrestrial climate, however, is still uncertain. So far, the impact of the compact cold clouds that are 4-5 order of magnitude denser than the ISM along the direct path of the Sun, was neglected. There is geological evidence from 60Fe and 244Pu isotopes that Earth was in direct contact with the ISM, about 2-3 million years ago. It is known that the local ISM is home to several nearby cold clouds. Using new modeling of 21-cm data from the HI4PI survey, we derive the velocity field of the Local Ribbon of Cold Clouds (LRCC). We show that the solar system may have passed through the Local Ribbon of Cold Clouds in the constellation Lynx(LxCC). The likelihood of a random encounter with a dense cloud is 1.3%. Using a state-of-the-art simulation of the heliosphere, we show that during the passage the heliosphere had shrunk to a scale of 0.22AU, smaller than the Earth’s orbit around the Sun. As a result, Earth was exposed to a neutral hydrogen density above 3000cm-3. This could have had drastic effects on Earth’s climate, as suggested by records of oxygen isotopes derived from forminifera in the sea floor and potentially on human evolution at that time where Australopithecus afarensis (“Lucy”) went extinct, leading to the emergence of the Homo lineage.