True. If you are in a trench, you are literally sitting in a hole in the dirt for hours on end; sometimes keeping watch, sometimes in the heat of battle. If you get injured, there are tons of diseases in the dirt and from humans just sitting in that hole for large amounts of time, usually without showering for days or weeks (depending on where you are and the resources available). Injury, you could get shot in the shoulder while firing, or someone could throw an active grenade into the trench and, well, it wouldn't end well. Mud-- you're sitting in a hole, in the dirt. If it rains, you are now sitting in a wet hole in the dirt, and dedication to your country--or flying bullets--is keeping you there.
the answer here is Abyssal Pains
The correct answer is - from solar nebula.
The Earth and the other planets in the Solar System are thought to have formed from solar nebula. This solar nebula is believed to have been a left over from the Sun's formation, being consisted of gas and dust in a disc-shape. The material in this disc-shaped gas and dust started to merge gradually, thus little by little forming bigger and bigger objects, and as the objects were getting bigger they had bigger gravitational pull so more and more material was attracted toward them. Because of the very big gravitational pull of the Sun these objects were not able to wander into the space but were instead kept close to the Sun. Because of the orbiting around the Sun, they all started to take a rounded shape. Some planets as the Earth, Venus, Mars, and Mercury became terrestrial planets, while the likes of Jupiter, Saturn, Uranus, and Neptune became gas giants.
The inner core is also believed to be moving at a different rate than the outer core. These swirling convection currents result in the earth's magnetic field which keeps us properly oriented for travel, and shields earth from deadly cosmic rays
