How are the chemical compositions of early galaxies compared to galaxies observed today?

Chemically primitive, lacking heavy elements

The chemical composition of galaxies is directly linked to the stellar life cycle. Stars are responsible for forging heavier elements (those beyond hydrogen and helium) through fusion and subsequently dispersing these elements into the interstellar medium when they die (through supernovae or stellar winds). Since the galaxies observed by Hubble were extremely young—existing when the universe was less than a billion years old—they had experienced far fewer generations of stars dying and enriching their material. Therefore, these early galaxies are described as chemically primitive because their gas clouds had a much lower abundance of these heavy elements compared to the complex chemical mixtures found in galaxies like the Milky Way today.