Some look like undersea gardens, gently blowing in the breeze.

Others look like alien brains.

But if I had to pick an analogy, I'd say this coral is like an ancient city under the waves.

Generations of tiny houses, stacked one on top of another over millennia.

The living part of the coral--the bright, beautiful parts you see--that's just what's at street level.

It's made of animals called polyps, living inside hard exoskeletons.

And when one polyp dies, another builds a new home right on top of the old one.

Go beneath the surface, and you find buried clues about the past.

Can you see in this cross-section, how coral grows in layers?

Kind of like tree rings?

Palaeoclimatologists study those rings to learn about ancient climate.

But there are some secrets you can't see with the naked eye.

So researchers at Stanford University are putting coral samples in an unlikely place.

A synchrotron.

One of the world's most powerful X-ray machines.

In fact it's 1 billion times brighter than a hospital X-ray machine.

The resolution is so high, that you can see weekly weather patterns from hundreds of years ago.

These bright spots in the X-ray have higher concentrations of the element strontium.

When the water is warmer, corals absorb less strontium.

When the water is colder, they absorb more.

So the amount of strontium in the coral can tell you a lot about ocean temperature.

Say you wanted to know when the rainy season began in a given year.

Well, to answer that, scientists look in the coral's skeleton for traces of barium.

An element found in soil.

When it rains, soil washes into the ocean, and gets absorbed by the coral.

Detailed written weather records have only been around for about 150 years.

But this coral sample from American Samoa is over 500 years old.

For the Palaeoclimatologists its like having a temperature gauge since the time of the conquistadores.

These tiny creatures, and the undersea cities they build still have a lot to tell us.

Maybe by analyzing ancient climate, we can be better prepared for the climate of the future.