Why does Earth have fewer hydrogen and helium gases than Jupiter and Saturn?

Earth has significantly fewer hydrogen and helium gases than Jupiter and Saturn primarily due to differences in mass, temperature, and gravitational retention during the formation of the solar system.1

A planet's ability to retain an atmosphere depends on its escape velocity—the speed required for gas molecules to overcome the planet's gravitational pull—relative to the average velocity of those gas molecules. Because hydrogen and helium are very light, they move at high speeds.12

Earth’s relatively low mass results in an escape velocity of 11.3 km per second. Early in its history, Earth's atmosphere was likely hot, causing light gases like hydrogen and helium to move faster than this escape velocity, allowing them to escape into space. In contrast, Jupiter and Saturn are much more massive and colder, which allowed them to gravitationally capture and retain large amounts of these primordial gases from the original solar nebula. Consequently, while the giant planets remain rich in hydrogen and helium, Earth’s atmosphere evolved to be composed of heavier volatile compounds.132