Why is hydrogen relatively scarce in Earth’s crust by weight?

Although hydrogen is the most abundant element in the universe, it makes up only about 0.14 percent of Earth’s crust by weight. Its relative scarcity in the crust is primarily due to the nature of Earth's formation and the physical properties of the element itself.1

Earth formed through the accretion of small solid objects, or planetesimals, which were composed largely of heavier elements. Because hydrogen is a very light gas, it was not effectively retained by the planet during its early, hot stages of formation. While hydrogen is present on Earth in vast quantities—primarily combined with oxygen to form water—it is not a major constituent of the solid rock that makes up the crust. Furthermore, hydrogen can be lost to space through the process of photodissociation, where ultraviolet light breaks down water vapor in the upper atmosphere into hydrogen and oxygen; the light hydrogen gas then escapes the planet's gravitational pull.231