Your motherboard is fine, and does support PCI-E 3.0 if you have a Core i5 or i7 3xxx CPU. Even if you have an older CPU that only supports PCI-E 2.0 it won't be a problem, the GTX 1070 isn't fast enough to fully saturate 16 lanes of PCI-E 2.0.
Your motherboard is fine, and does support PCI-E 3.0 if you have a Core i5 or i7 3xxx CPU. Even if you have an older CPU that only supports PCI-E 2.0 it won't be a problem, the GTX 1070 isn't fast enough to fully saturate 16 lanes of PCI-E 2.0.