Elemental abundances refer to the relative amounts of different chemical elements found in a specific environment, such as the Earth, the universe, or a star. These abundances are often expressed as a percentage or in parts per million (ppm). For example, in the Earth's crust, the most abundant elements include oxygen, silicon, and aluminum. In astronomy, elemental abundances help scientists understand the composition of celestial bodies and the processes that formed them. By studying the light emitted or absorbed by stars, researchers can determine the presence of elements like hydrogen, helium, and heavier elements, providing insights into the history and evolution of the universe.