Polycrystalline diamond compacts, cutting elements and earth-boring tools including such compacts, and methods of forming such compacts and earth-boring tools

A method of drilling, comprising:

• engaging at least one cutter with a formation, the at least one cutter including a diamond table comprising:
• a first region of polycrystalline diamond material comprising a first material in interstitial spaces between inter-bonded diamond crystals in the first region of polycrystalline diamond material;
• and
• a second region of polycrystalline diamond material comprising a second material in interstitial spaces between inter-bonded diamond crystals in the second region of polycrystalline diamond material, the second material inducing a higher rate of degradation of the polycrystalline diamond material than the first material under approximately equal elevated temperatures;
• and
• wearing the second region of polycrystalline diamond material faster than the first region of polycrystalline diamond material by forming a recess in the second region in a portion of a sidewall of the diamond table and spaced from a cutting face of the diamond table as friction from engagement of the at least one cutter with the formation increases the temperature of the first region and the second region.

A polycrystalline diamond compact (PDC) cutting element for use in an earth-boring tool, comprising:

• a first region of polycrystalline diamond material comprising a first material in interstitial spaces between inter-bonded diamond crystals in the first region of polycrystalline diamond material;
• and
• a second region of polycrystalline diamond material comprising:
• a region extending around at least a portion of a periphery of a sidewall of the PDC cutting element and spaced from a cutting face of the PDC cutting element;
• and
• a second material in interstitial spaces between inter-bonded diamond crystals in the second region of polycrystalline diamond material, the second material inducing a higher rate of degradation of the polycrystalline diamond material than the first material under approximately the same elevated temperature.

An earth-boring tool, comprising:

• a body;
• and
• at least one polycrystalline diamond compact (PDC) cutting element attached to the body, the at least one PDC cutting element having a diamond table on a surface of a substrate, the diamond table comprising:
• a first region of polycrystalline diamond material disposed at least adjacent a surface of the substrate, the first region comprising a first material in interstitial spaces between inter-bonded diamond crystals in the first region of polycrystalline diamond material;
• and
• a second region of polycrystalline diamond material spaced from a cutting face of the diamond table between the first region of polycrystalline diamond material and a side of the diamond table, the second region comprising a second material in interstitial spaces between inter-bonded diamond crystals in the second region of polycrystalline diamond material, the second material promoting a higher rate of degradation of the polycrystalline diamond material than the first material under substantially equivalent elevated temperatures.