There is a long list of naturally occurring processes in the earth which can serve as time clocks.  Consider the rate of erosion of Niagara Falls.  At about 6 feet per year it is reasonable to calculate that it took about 6000 years to form the 35,000 foot gorge we see today.

Another river based natural time clock is the Mississippi River delta.  Considering its size and rate of sedimentation, its age is determined to be about 4000 years.

The level of concentration of various elements in the earth's oceans is still another example of a natural time clock.  Even with generous allowances for processes that remove these elements from the ocean waters (sink rates), calculations do not yield an earth anywhere near old enough to make evolution a possibility.  These calculations are even so gracious as to assume that the oceans began with none of these elements present.  Depending on the element, calculated earth ages can range as high as 260 million years, but some are lower by several orders of magnitude.  Of course much lower numbers are required if the oceans did not begin as pure water or if the gracious sink rates are too generous.

The earth's magnetic field is steadily decaying.  Measurements recorded over the last 160 years demonstrate that the rate of decay is steady over that period, having a half life of about 1400 years.  Calculating back 10,000 years yields a magnetic field 32 times stronger than today.  Such a field would have rendered life on earth a practical impossibility.  Also, no one has yet been able to postulate a  process that might have produced a field of such intensity.

Of course we all know that the earth is cooling as it ages.  Just as a heated rock eventually assumes the surrounding temperature, so the heat in the earth's core is slowly being lost into space.  Where the old earth theory runs into trouble is when this rate of cooling is extrapolated back about 20,000 years.  At that point the earth's temperature would have been high enough to keep everything in a molten state.

These are just 5 examples out of scores of natural time clocks that contradict claims of an earth that is over 4 billion years old.  Each time clock is a process that is observable and measurable, and those processes may be repeated over and over by any one who wishes to do so.  This is good science.  Only a closed mind will cast aside such data.