Figure 3A.
The eon of the Proterozoic was once called "Precambrian" but is now just a portion of what we now call the entire time before the Cambrian boundary. This period was itself divided into three eras, called the Neo-, Meso-, and Paleo-proterozoic eras. These correspond to the Precambrian Z, Y, and X rock strata in North America, respectively.
THE EARTH'S SPHERES You have probably heard of the spheres of our atmosphere – like the stratosphere, etcetera. The earth itself is part of that sphere system; this means that the ground itself and parts beneath it are included in these spheres. Honestly, you need all the spheres around earth to work together for Earth's sustainability as a planet. The lithosphere is the "rock" part of the earth. This includes both the interior rocky parts and the rocky surface of earth. The sphere outside of that is the biosphere, which 24
