Wegener also noted that the continents move up and down to maintain equilibrium in a process called isostasy. As an example he cited the sinking of Northern Hemisphere lands under the weight of continental ice sheets in the last ice age, and their rise since the ice melted some 10,000 years ago.
Drill bits are cutting tools used to create cylindrical holes, almost always of circular cross-section. Drill bits come in many sizes and have many uses. Bits are usually connected to a mechanism, often simply referred to as a drill, which rotates them and provides torque and axial force to create the hole.
The use of a seed drill can improve the ratio of crop yield (seeds harvested per seed planted) by as much as nine times. Some machines for metering out seeds for planting are called planters. The concepts involved (such as mechanisms that pick up seeds from a bin and deposit them down a tube) are largely the same.