Paleontology and geologyThe oldest rocks in Mexico are ~1.8 Ga metamorphic rocks exposed in the northern part of this region. These and other Precambrian metamorphic and igneous rocks formed near the edge of the ancient North American continent (Laurentia). From about 1.0 to 0.75 Ga, Laurentia was part of a supercontinent called Rodinia, with Mexico near the center. After the supercontinent broke up, the seas returned to cover the northern part of this region. Sandstones, mudstones, and limestones deposited in the shallow waters preserve stromatolites, as well as some of the earliest multicellular animals, like disc-shaped Cyclomedusa and Sekwia, and cone-shaped Cloudina. Some of these Precambrian rocks may have formed in what is now California and been moved to their present location in Mexico. Geologists continue to study how and when these deposits developed. The rest of the northwestern region of Mexico had not formed yet. |
