Final answer:
The subject of this question is Geography, specifically focusing on North America during the mid Proterozoic era. This era was part of the larger Paleozoic era, which involved the formation of supercontinents, changes in climate, and the evolution of vertebrates.
Step-by-step explanation:
The subject of this question is Geography. The question is asking about the North America in the mid Proterozoic era, specifically between 1.6 and 1 billion years ago.
During this time, the supercontinent Gondwana existed, which began to break up during the Jurassic period. The Paleozoic era, which includes this time period, was marked by the formation of supercontinents, changes in climate and sea levels, and the evolution and distribution of vertebrates.
Keywords: North America, mid Proterozoic, Gondwana, supercontinent, Paleozoic era, climate, sea levels, vertebrates.