The RATE project from ICR has been examining the limits and data around C14 radioisotope dating methods, and one of the their last experiments seems to strongly, if not unequivocally, support a young earth perspective.  Simply put, since C14 has a very short half life, in many presumably old carbon and diamond samples, there should be NO C14 left at all – it should have all decayed.  However, even secular scientists admit that there are much higher than background levels in such samples.  Why? 

The data looks like this:

Ten samples from U.S. coal beds, conventionally dated at 40–320 million
years old, were found to contain carbon-14 equivalent to ages of around
48,000–50,000 years.

OK, so that undercuts the old earth position, but isn’t that about 10x the normal age that young earthers claim?  Yes, but that’s a separate discussion, one based on the actual rates of decay, which young earthers claim was FASTER in the past, so these numbers may still be inflated – but even if you assume today’s rate of decay as constant over time, the million year old numbers are outlandish.

Not only did they control for possible errors, making sure that the C14 was intrinsic (in situ) to the carbons and diamonds, but they also cite existing studies from the University of California:

Confirmation that there is in situ carbon-14 in diamonds has now been reported in the conventional literature.3 R.E. Taylor of the Department of Anthropology at the University of California–Riverside…analyzed nine natural diamonds from Brazil. All nine diamonds are
conventionally regarded as being at least of early Paleozoic age, that
is, at least several hundred million years old. So, if they really are
that old they should not have any intrinsic carbon-14 in them.

So what did the UC scientists find?

Eight of the diamonds yielded radiocarbon “ages” of 64,900 years to
80,000 years. The ninth diamond was cut into six equal fragments, which
were each analyzed. They yield essentially identical radiocarbon “ages”
ranging from 69,400 years to 70,600 years. This suggests the carbon-14
was evenly distributed through this diamond, which is consistent with
it being intrinsic carbon-14, and not contamination.

What does this mean?  The creationist explanation is clear and easy – the earth MUST be young, and possibly, the rate of decay was faster in the past.  And what explanation do the UC scientists give?  You won’t believe how weak their answer is:

The University of California scientists, of course, did not conclude
that the diamonds they analyzed are evidence that the earth is young.
Instead, they interpreted these 64,900–80,000 year “age” to represent
one component of “machine background” in the analytical instrument.

If you read the article, you’ll see why this explanation does not make sense, in light of their varied results on other samples – how did the "machine background" change while still giving relatively young ages? 

The young earth movement has some great data behind it, and this is just some.