There are three standard creationist responses: First, creationists assert that current rates (Y) are different than past rates.
Carbon dating can only be used to date objects that were once living or even apart of a living organism. It cannot be used to directly date inorganic objects, such as rocks (other radioactive dating methods are used to date radioactive rocks).
Radioactive atoms are inherently unstable; over time, radioactive "parent atoms" decay into stable "daughter atoms." When molten rock cools, forming what are called igneous rocks, radioactive atoms are trapped inside. By measuring the quantity of unstable atoms left in a rock and comparing it to the quantity of stable daughter atoms in the rock, scientists can estimate the amount of time that has passed since that rock formed.
Fossils are generally found in sedimentary rock not igneous rock.
The fact is, carbon dating can only be used to date things up to approximately 50,000 years old.
In fact, if an object contains (radioactive) carbon, this should be a clue that the object may not be any older than 50,000 years.
Scientists date igneous rock using elements that are slow to decay, such as uranium and potassium.