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 that is fitted with a Pipe provides effective connection to the rig surface equipment or application with the bit and the bottom hole assembly for the purpose of pumping the Drill fluid to the bit.
The bow drill is an ancient form of drilling tool. It commonly was used to make friction fire, and in this function it also was called a fire drill. However, the same principle also was used widely in drilling for purposes of woodworking and dentistry. Bow drill is used to get an ember (left), the ember makes tinder smoke (center), until a fire is lit (right). Whilst a v is most common, other methods to create a cavity to contain the dust whilst it is being ignited can be used.