How does Masaccio use light and dark to model Adam and Eve in Expulsion from Paradise?

In his fresco Expulsion from Paradise, Masaccio constructs the figures of Adam and Eve using strongly differentiated areas of light and dark rather than relying on line.1

This technique creates a pronounced three-dimensional sense of relief, giving the figures a volumetric and expansive quality. By utilizing these light and shadow effects, Masaccio makes the figures appear as though they exist within the spectator's own world, illuminated by natural light. This approach was a significant departure from the artistic conventions of the Middle Ages, as it helped establish the concept of a painting as a window into a continuation of the real world, governed by consistent physical laws of light and form.12