The process that continually adds new crust is

The correct answer is seafloor spreading.

Key PointsSeafloor Spreading:

• Seafloor spreading is a geologic process in which tectonic plates large slabs of Earth's lithosphere split apart from each other.
• Seafloor spreading and other tectonic activity processes are the result of mantle convection.
• Mantle convection is the slow, churning motion of Earth’s mantle.
• Convection currents carry heat from the lower mantle and core to the lithosphere.
• Convection currents also “recycle” lithospheric materials back to the mantle.
• Seafloor spreading occurs at divergent plate boundaries.
• As tectonic plates slowly move away from each other, heat from the mantle’s convection currents makes the crust more plastic and less dense. The less dense material rises, often forming a mountain or elevated area of the seafloor.
• Eventually, the crust cracks. Hot magma fueled by mantle convection bubbles up to fill these fractures and spills onto the crust. This bubbled-up magma is cooled by frigid seawater to form igneous rock. This rock (basalt) becomes a new part of Earth’s crust.
• This process that continually adds new crust to the Earth's surface is called seafloor spreading.

• This geological phenomenon occurs along mid-ocean ridges, which are underwater mountain ranges that run through the world's oceans.