A method of forming a cutting element for an earth-boring tool, comprising: providing a first powder comprising diamond crystals adjacent a surface of a cutting element substrate; providing a layer of barrier material adjacent the first powder on a side thereof opposite the cutting element substrate; providing a second powder comprising diamond crystals adjacent the layer of barrier material on a side thereof opposite the first powder; subjecting the cutting element substrate, the first powder, the layer of barrier material, and the second powder to high temperature and high pressure conditions in order to sinter them, and forming a first layer of polycrystalline diamond material from the first powder and a second layer of polycrystalline diamond material from the second powder; catalyzing the formation of at least the first layer of polycrystalline diamond material from the first powder using catalytic material for catalyzing the formation of polycrystalline diamond material from individual diamond crystals; catalyzing the formation of the second layer of polycrystalline diamond material from the second powder using additional catalytic material for catalyzing the formation of polycrystalline diamond material from individual diamond crystals; hindering the catalytic material from migrating across the layer of barrier material; and removing catalytic material from interstitial spaces between diamond crystals in the second layer of polycrystalline diamond material after subjecting the cutting element substrate, the first powder, the layer of barrier material, and the second powder to high temperature and high pressure conditions in order to sinter them, and forming a first layer of polycrystalline diamond material from the first powder and a second layer of polycrystalline diamond material from the second powder; wherein the barrier material is selected from the group consisting of tantalum, titanium, tungsten, molybdenum, niobium, and alloys and mixtures thereof. providing a first powder comprising diamond crystals adjacent a surface of a cutting element substrate; providing a layer of barrier material adjacent the first powder on a side thereof opposite the cutting element substrate; providing a second powder comprising diamond crystals adjacent the layer of barrier material on a side thereof opposite the first powder; subjecting the cutting element substrate, the first powder, the layer of barrier material, and the second powder to high temperature and high pressure conditions in order to sinter them, and forming a first layer of polycrystalline diamond material from the first powder and a second layer of polycrystalline diamond material from the second powder; catalyzing the formation of at least the first layer of polycrystalline diamond material from the first powder using catalytic material for catalyzing the formation of polycrystalline diamond material from individual diamond crystals; catalyzing the formation of the second layer of polycrystalline diamond material from the second powder using additional catalytic material for catalyzing the formation of polycrystalline diamond material from individual diamond crystals; hindering the catalytic material from migrating across the layer of barrier material; and removing catalytic material from interstitial spaces between diamond crystals in the second layer of polycrystalline diamond material after subjecting the cutting element substrate, the first powder, the layer of barrier material, and the second powder to high temperature and high pressure conditions in order to sinter them, and forming a first layer of polycrystalline diamond material from the first powder and a second layer of polycrystalline diamond material from the second powder; wherein the barrier material is selected from the group consisting of tantalum, titanium, tungsten, molybdenum, niobium, and alloys and mixtures thereof.