How Do Paleontologists Remove Fossils From Rock?

Saturday, May 15, 2021

Fossilized in-ground Stegosaurus at Houston Museum of Natural Science

Ancient bones and teeth gleam under bright lights in the Melbourne Museum, surrounded by throngs of excited children — and more than one captivated adult.

But beneath this hustle and bustle, in the building's basement, is where such fossils are broken out of their rocky tombs and cleaned up for display and scientific research.

Pieces of limestone at various stages of processing lie around the room. They're all sizes — from tiny delicate bones lodged in matchbox-sized pebbles to hefty slabs that need a hydraulic lift to move them around.

And forget what you saw on Jurassic Park, where palaeontologists gently sweep sand and stones away from perfectly preserved skeletons. In reality, it's a much noisier process.

Fossils last millions of years because, quite often, they're surrounded by hard rock.

So palaeontologists often enlist the help of special power tools, plus acid — and a whole lot of patience.

Rocking out

Many of the bones and teeth in the museum's basement are the fossilised remains of ancient whales and dolphins that swam the oceans 15 million years ago.

When they died, the animals' bodies sank to the sea floor and were covered in silt and mud. Over time, that squishy sediment solidified into limestone.

These days, that limestone forms towering wheat-coloured cliffs that trace Victoria's Surf Coast. As the wind and waves bash away at the cliffs, they expose bones and teeth embedded within, which are sometimes spotted by eagle-eyed surfers and fossil-hunters.

Palaeontologist Ben Francischelli is one such fossil-hunter. He is part of a group that regularly scouts the coast at low tide for ancient remains, which stand out black against the limestone.

And while finding a fossil takes some skill, that's the easy part compared to what's to come.

Before trying to remove a fossil they've found, they pour on and soak it in a liquid called paraloid that cures like a glue, giving strength to the ancient remains.

Then if they can, the crew uses chisels and crowbars to safely remove the fossil and surrounding chunk of limestone, which they then load into a waiting car. This can be hard yakka ... but the hardest work happens back at the museum.

The limestone and embedded fossil is taken to the Melbourne Museum basement. Here, the process begins to remove the fossil from its rocky nest where it's rested for millions of years.

Chemical help

First, palaeontologists need to remove as much of the surrounding limestone as possible without damaging the precious fossil within. Often this means sticking it in acid for a couple of days.

To do this, the fossil is taken to the museum's acid process room, where plastic tubs and sinks line the walls.

Despite being quite hard, limestone — which is made of a material called calcium carbonate — dissolves in acid.

Pop a piece of limestone in acetic acid, also known as vinegar, and bubbles of carbon dioxide start forming on the rock surface.

The paraloid, which the fossil-hunters added earlier, helps protect the fossil from the acid. Palaeontologists will often also coat the exposed fossil with lacquer too.

After a couple of days, depending on the volume of limestone, the fossil is flushed with fresh water to wash away calcium salts that build up during the chemical reaction between the acetic acid and calcium carbonate.

Then it's time to give the fossil its first clean, Dr Francischelli says.

"[The acid bath] usually turns some of the sediments into a slush, which we can then just gently wipe away with a brush," he says.

And then he brings out the power tools.

The big guns

Next door to the acid process room is the main fossil preparation workshop.

It has tall ceilings and industrial fans, a little like a standard workshop, but instead of an array of screwdrivers and drills, these tools range from delicate brushes to modified dentist drills.

Before getting stuck into the fossil, Dr Francischelli says, "you have a look at the ways in which the bone is contouring through it, because that very first bath usually strips a lot of the surrounding sediment".

"And then you've got to ask yourself the question: do I need to trim this specimen down further?

"If that is the case, then you'd get the big guns out."

The big guns aren't as big as your standard household drill, but these palaeo-tools pack a punch.

Before getting started, Dr Francischelli dons protective ear wear, goggles and mask, because this part is incredibly noisy and dusty.

The air chisel chips away at the rock while the fine-tipped drill is best used for the most delicate work. Still, the sound is not pleasant, to say the least.

And not everything always goes to plan.

"This limestone’s really hard," Dr Francischelli yells over the drill. "It dents the tools every now and again."

Sometimes, the bone can shatter — perhaps because it was accidentally hit by a tool or simply vibrated too much.

When that happens, so begins the slow job of picking up all the shards and painstakingly gluing them together again.

Once the fossil is cleaned up, Dr Francischelli says, he and his colleagues can properly identify exactly what it is they have.

"And if we know that we've got something special, which is why we take the time to actually prepare it in the first place, we can try and figure out what kind of species it is, [or] if it's a new species," he says.

"And if that is the case, or if it's something really important, we can name it in a paper, we can describe it in the scientific literature, and use it to educate the masses about palaeontology as a whole."