We use the distribution of low-Lu and low-Lu/Dy zircons, derived from the eroded roots of mountains, where trace amounts of zircon compete with abundant garnets for heavy rare earth elements, to identify periods of extensive high mountain (supermountain) formation. The data reveal that Earth has two, and they correlate with periods when the average metamorphic pressure of orogenic belts exceeded 1.2 GPa, the pressure at which metamorphic garnet becomes abundant. The first supermountains formed at 2.0-1.8 Ga, during the assembly of Nuna, and the second at 650-500 Ma, during the amalgamation of Gondwana. The 650-500 Ma event has been previously recognized and named the Transgondwanan Supermountain, but the 2.0-1.8 Ga Nuna Supermountains have not. Our data also show that mountain building was limited during the Boring Billion, between 1.8 and 0.8 Ga. Mountain building results in high rates of erosion and sedimentation, and the two periods of supermountain formation are associated with voluminous sedimentation, whereas sediment production during the Boring Billion was more limited. Enhanced erosion would have increased the supply of bio-limiting nutrients such as phosphorous to the oceans, potentially increasing primary productivity and the flow of energy through ecosystems. Enhanced carbon production and sedimentation, both driven by supermountain erosion, are also expected to lead to increases in atmospheric oxygen. During Transgondwanan Supermountain erosion, increasing oxygen and nutrient levels may be connected to the proliferation of chlorophyte algae after 650 Ma and the emergence of large, animal-like organisms 75 Myr later. Targeted research of Nuna-aged sediments is needed to evaluate whether rapid erosion of supermountains is linked to geochemical and biotic events, such as the disappearance of banded iron formations at 1.85 Ga, the emergence of the first macroscopic organisms (Grypania) at 1.9 Ga, and the radiation of early eukaryotes, which become visible in the fossil record at 1.65 Ga.