The Bimini Road is a series of large,   oblong stones half-buried along the  coast of a small island in the Bahamas.

They look like a cobblestone road for giants,  which has led some people to believe that   they’re manmade, and possibly even the  remains of the lost city of Atlantis. Sadly, we’re pretty sure that’s not the case.

But the scientific explanation for how these  manufactured-looking rocks formed is just as cool! And while they’re almost certainly  natural, they serve an important purpose. So scientists are looking into how  to recreate them all over the world. [♪ INTRO] Formed from rectangular limestone blocks,   the Bimini Road extends almost 1 kilometer into  the ocean off the coast of North Bimini island.

It does really look manmade, hence  all the speculation about its origin. People have claimed that the road  was constructed in the 1400s by a   shipwrecked Chinese general, that  it’s evidence of ancient aliens,   and perhaps most persistently, that the  Bimini Road is proof that Atlantis exists. Now, you’ve probably guessed that the Bimini Road   isn’t actually a hallmark  of Atlantean civilization.

So the real question is, what is it? As artificial as it looks, the  Bimini Road is 100% natural. The road’s stones are made up  of beachrock, which is a hard,   sedimentary rock that forms when  beach sediments get glued together.

There’s a lot of variation in beachrock sizes,   anything from tiny patches to huge  blocks, hundreds of meters wide. Beachrocks are found all over the world, although  they have a tendency to form in warmer waters,   so they’re common in places like the  Caribbean, Australia, and the Mediterranean. They also tend to form along coastlines  known as microtidal coasts, which are   areas of the world where there isn’t too much  difference between low tide and high tide.

Knowing that they like to form in warm,   still waters already gives us some  clues about how these beachrocks formed. And we get the rest of the story by  taking a look at their chemical make-up. Beachrocks are bound together  by calcium carbonate.

Calcium carbonate is a pretty common mineral. It exists naturally in two main  forms called calcite and aragonite,   which are chemically identical, but differ  slightly in their mineral structure. Both calcite and aragonite  form naturally out of seawater.

That’s because seawater contains  both positively charged calcium   ions and negatively charged carbonate ions. These ions are all floating around in water,  and when they collide and bond with each other,   they form solid calcium carbonate,  which precipitates out of solution. This is more likely to happen in warm water,   because of something interesting  about how carbonate ions work.

Carbonate ions are part of  the ocean carbonate system,   which is made up of carbonate,  bicarbonate and carbon dioxide. These three ions are all in  balance when in seawater,   and anything that affects  one will mess with them all. Carbon dioxide dissolves more easily in  cold water, and as the water warms up,   carbon dioxide leaves solution  and enters the atmosphere.

Lowering the amount of carbon dioxide in  seawater changes the concentrations of the other   ions in the system, because the whole system  needs to work to get back into equilibrium. This makes carbonate ions more  likely to want to bond with calcium,   resulting in calcium carbonate,  and rebalancing the ion levels. This is even more likely to happen in water that  isn’t being moved around a lot by the tides.

It’s kind of like when you  stir sugar into cold water,   and there’s that pile of it in the  middle where the spoon didn’t reach. So calcium carbonate crystals grow  in these warm, non-turbulent waters. And as they grow, they mix in with the sand and  grit around them, creating a kind of concrete.

Having hard objects in the sand at the coast is   going to have an effect on the way  water interacts with the shoreline. We’re still working on quantifying that effect,  because wave dynamics are really complex and   difficult to model, and beachrocks aren’t  the same as artificial concrete barricades. But it appears that on islands like North Bimini,  beachrocks prevent the shoreline from eroding.

The prevailing theory is that beachrocks  act as a sort of natural defense against erosion,   locking in the shape of the beachfront, like  a retaining wall on the edge of a steep hill. Because of this, there’s been some recent  work into making artificial beachrocks,   to protect some vulnerable  places from eroding away. And it isn’t just beaches that will benefit  from us learning how to make this material.

Like I said, beachrocks are a  naturally occurring type of concrete. And some researchers are looking into how we  can use them to change the way we make concrete. That’s because the best way we have  of making cement involves heating   the cement mixture in a kiln, reaching  temperatures of over 1400 degrees Celsius.

That process causes a lot of carbon  dioxide emissions, and with cement   being the basis of most building materials  in the world, those emissions really add up. About 8% of global carbon dioxide  emissions come from cement production,   and heating the cement is especially bad. But beachrocks, on the other hand, form at  normal, everyday temperatures, no heat required.

So that means if we could figure out how  to make our cement at low temperatures,   we could have a cement alternative  that really cuts down on emissions. Plus, creating a material that basically  grows itself could mean that we could also   create a material that repairs itself  over time, saving on maintenance costs. So while they’re not the  remnants of a lost civilization,   beachrocks could still be part  of a high-tech, greener future.

And hopefully, it’s one that keeps  us from ending up underwater, too. This video was inspired by the book Megalodons,   Mermaids, and Climate Change,  by Ellen Prager and Dave Jones. In addition to explaining The Bimini Road,   it answers dozens of other questions  about the oceans and atmosphere.

If you’d like to check it out,  head to the SciShow Bookshop page. This video was made possible by  the Alfred P. Sloan Foundation. [♪ OUTRO]