The deep sea is defined as any marine water body deeper than 200 m, and it is divided into the bathyal (200–3000 m), abyssal (3001–6000 m), and hadal (6001–10,900 m) zones. The abyssal zone is typified by the flat abyssal plains, while the hadal zone comprises the ocean trenches, down to the Challenger Deep, the deepest point in the oceans. The deep sea is usually cold (2–4°C; 36–39°F), and the weight of the overlying water exerts massive pressure, 1 atmosphere for every 10 m of water depth. Light is strongly absorbed by seawater; thus by 1000 m, no detectable sunlight is present. Since plant photosynthesis cannot occur without light, there is no primary productivity to provide food for animals. Most of the food for deep-sea animals falls from the surface (possibly after being eaten by at least one other animal), and there is little left by the time it reaches the deep seafloor.