NASA-funded studies indicate that ancient variations in the Sun’s environment may have influenced Earth’s climate, including periods of ice age and the Faint Young Sun paradox. The Sun’s heliosphere, a bubble of solar wind that envelops the solar system, moves through the Milky Way galaxy; its trajectory may have altered Earth’s atmospheric conditions. Researchers at NASA’s SHIELD center used computer models to reconstruct the heliosphere’s path over billions of years and identified three intervals when it passed through dense interstellar clouds approximately 2–3 million, 6–7 million, and 13–14 million years ago, causing the heliosphere to shrink below Earth’s orbit. Geologic evidence shows that elements from interstellar dust appear in deep‑sea sediment cores, Antarctic snow, and lunar samples during those times. Simulations suggest that exposure to these cold clouds increased water vapor and shifted upper‑atmospheric dynamics, potentially contributing to cooling and ice age cycles. In a separate study, NASA scientist Vladimir Airapetian and colleagues investigated how the early Sun, which was about 70 percent as bright as today, could have warmed early Earth. Observations from the Kepler space telescope show that young Sun‑like stars emit frequent superflares that release high‑energy particles. Laboratory experiments that simulated an early Earth atmosphere bombarded with protons produced nitrous oxide, a strong greenhouse gas about 300 times more potent than carbon dioxide. Even if only about 10 percent of the nitrous oxide survived the young Sun’s ultraviolet radiation, climate models indicated that it could raise equatorial temperatures to roughly 41 degrees Fahrenheit (5 degrees Celsius), above the freezing point of water, and may have facilitated prebiotic chemical reactions. Together, the studies suggest that solar activity and heliospheric interactions have had measurable effects on Earth’s climate and habitability. Further research is needed to determine the magnitude of these influences.