What are tectonic plates?

Tectonic plates are best described as large movable plates that make up the Earth's lithosphere. The lithosphere is the rigid outer layer of the Earth, which includes both the crust and the upper mantle. These plates are constantly in motion, albeit very slowly, due to the convection currents in the underlying semi-fluid asthenosphere.

This movement can result in various geological phenomena, such as earthquakes, volcanic activity, and the formation of mountains. The interactions between the plates, including their boundaries where they converge, diverge, or slide past each other, are vital to understanding the dynamics of Earth's surface and its geological history.

In contrast, some of the other options do not accurately characterize tectonic plates. For instance, describing them as stationary blocks of the Earth’s crust does not reflect their dynamic nature. Saying they are small, rigid pieces implies a level of size and immobility that doesn't represent the larger scale and movement involved with tectonic plates. Likewise, stating that they are fixed layers of the Earth's atmosphere misidentifies their geological context entirely, as tectonic plates are part of the Earth's solid structure, not its atmosphere.