A team of Israeli and German scientists from Ben-Gurion University of the Negev and the Max Plank Institute of Colloids and Interfaces in Potsdam, Germany have found an enamel-like layer in the mandibles of a type of freshwater crayfish that bears an astonishing resemblance to human enamel. The team recently published their findings in Nature Communications.

Enamel is by far the hardest mineralized tissue in the human body. Human bones and teeth gain their incredible strength and hardness from the use of calcium phosphate minerals. In contrast, like most invertebrates, freshwater crayfish reinforce their exoskeletons with a different calcium-based mineral: calcium carbonate (limestone). Biotechnology engineer Dr. Amir Berman and life sciences Prof.

Amir Sagi, in cooperation with Dr. Barbara Aichmayer and colleagues from Max Planck, have investigated the mandibles of the Australian freshwater crayfish Cherax quadricarinatus.

Dr. Shmuel Bentov from the BGU team discovered that this species of crayfish protect their teeth against wear in a very specific and surprising manner: they produce a highly mineralized protective coating based on calcium phosphate, strikingly similar to the enamel of vertebrates.

“Enamel is the best solution for coating chewing organs. We assume that in the course of evolution, both vertebrates and this crayfish independently developed enamel-like tissues to address similar needs. Crustaceans discard their old teeth during the molting events several times throughout their life, and grow new exoskeletons and teeth regularly and rapidly.”

The mandibles of the freshwater crayfish are part of their exoskeleton, which is regularly molted and renewed to allow growing to their next growth stage. The crayfish exoskeleton is embedded with the mineral calcium carbonate in amorphous form. This is of vital importance because the the amorphous, disordered state of the mineral facilitates its dissolution before molting.

The dissolved calcium carbonate is partly reabsorbed and used for the buildup of the new exoskeleton. However, the amorphous mineral is also less hard, hence is inappropriate material for making teeth, so there is a need for a hard coating to cover the tooth surface.

The team discovered that the solution that had evolved in the crayfish is coating the tooth surface with a layer of elongated calcium phosphate crystals that are organized perpendicular to the tooth surface, forming a dense, organized structure reminiscent of enamel, the existence of which in invertebrates was unknown until now. As a result, the crayfish tooth’s mechanical performance is remarkably similar to enamel. The crystalline structure, uniform orientation and dense packing of the crystals confer upon these layers the required hardness and strength. For these reasons, enamel is considered a “masterpiece” of biological mineralization.

NON-FLIPPING MAGNETIC POLES Were the Earth’s magnetic poles stable between 83 million and 121 million years ago? Research by Ben-Gurion University geologist Dr. Roi Granot, published recently in Nature Geoscience, has helped to answer this question. Granot and his international team trailed magnetometers across the North Atlantic to measure the magnetization of the rocks that form the ocean’s floor.

“For the past 83 million years, the northern and southern magnetic poles have been flipping back and forth up to five times every million years. But there were 38 million years without any reversals between 121 million years ago and 83 million years ago. We know that from using the magnetization of various geological records from that period,” Granot says.

The obvious question is why the geomagnetic field remained stable for so long. Based on sophisticated numerical simulations, the assumption was that the geomagnetic field was very strong and stable during this period. But until now, no firm evidence was available to confirm this prediction, since studying rocks on land means studying an incomplete record.

“Another way to approach this problem is to look at the oceans, because the oceans are like giant tape recorders. You can tow a magnetometer behind a ship and measure magnetic anomalies. These anomalies reflect the magnetization of the rocks underneath the ocean and therefore provide a continuous record of the evolution of the geomagnetic field,” he says.

“The caveat in using this method is that these magnetic anomalies also reflect other geological processes, possibly causing ambiguous results. One way to compensate for that ambiguity is to compare oceans. If you see the same pattern of magnetic anomalies at different locations around the globe, then you know it’s a geomagnetic field signature.

We compared the North Atlantic findings to different magnetic data from widespread oceans – the South Atlantic and the Indian Oceans. We saw that the signal was convincingly similar,” Granot explains.

What he and his colleagues discovered was that what has been known until now as the Quiet Zone actually contained a surprising story. “The signal was relatively stable in the beginning, then very noisy in the middle, then back to a relatively stable period toward the end,” Granot says. “What it means is that the conditions in the outer core evolved in a way that we didn’t know or expect. We can use it to better model the convection processes in the core and understand why the poles flip over and why they don’t,” he added.

“Traditionally, magnetic anomalies are used to date the oceanic basins. That’s how we date the ocean’s crust. These 38 million years, seemingly without reversals of the magnetic poles, couldn’t be precisely dated. Now we hope we can start dating the crust with these new anomalies. This area represents a quarter of the Earth’s oceans.”

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