Two atomic weights indicate the existence of pre-electronic forms of lead, with the original formation weighing slightly more than that produced through uranium disintegration. [1] Early lava flows brought up lead, copper, and iron to the surface, crumpling the earth's oldest fossil-bearing stratum. [2] Lead is found in Silurian deposits along with gas, oil, and zinc, representing the sedimentation of sluggish bodies of water. [3]