The sad fate of the old, well-armed sailors
In the Cambrian period, 500 million years ago, the armored set ruled the seas. Soft-bodied animals secreted a mineral paste that hardened into protective shells of immense strength and decorative beauty, some in the shape of ram’s heads or eagle’s wings, others like champagne flutes studded with dagger-sharp spines.
But by the Devonian some 70 million years later, most of these brachiopods, briopods, and related well-shelled sailors were extinct, victims of theft and their own extravagant ways.
as researchers recently introduced in the journal Trends in Ecology and Evolution, the collapse of the brachiopod kingdom exemplifies a struggle that defined life from the beginning: the search for phosphorus. Scientists have long known that the element phosphorus is essential on many fronts, here it holds the DNA molecule together, there it drives every movement of the cell. The new report highlights yet another way in which phosphate — the biochemically useful form of phosphorus — has shaped the course of evolution as an arbiter of nature’s hard parts, its shells and teeth and bones.
“Phosphorus was stolen by the vertebrates, the bony fishes,” said Petr Kraft, a paleontologist at Charles University in the Czech Republic and an author of the new report. “And once this happened, they quickly diversified and took over.” dr. Kraft collaborated with Michal Mergl from the University of West Bohemia.
The research is part of a renaissance of phosphate studies, a venture that spans disciplines and time spans. Chemists investigate how phosphates managed to spice up the prebiotic broth that gave birth to life in the first place, while materials scientists manipulate the element into surprising new colors and shapes.
“If you heat phosphorus under different conditions, different temperatures, different pressures, strange things happen,” said Andrea Sella, a professor of inorganic chemistry at University College London. “You get red fibrous shapes, metallic black shapes, purple shapes.” You can also stack layers of phosphorus atoms on top of each other and then pull them apart into ultra-thin and flexible sheets called phosphorenes, all for the purpose of controlling the flow of electrons and light particles on which the technology relies. “We’ve only scratched the surface of what this element can do,” said Dr. sella.
Phosphorus was discovered in the late 1600s by a Hamburg alchemist, Hennig Brand, who accidentally isolated it while searching for the legendary “philosophers’ stone” that would turn ordinary metals into gold. Fluently experimenting with large amounts of the golden liquid he knew best – human urine – Brandt emerged with an eerie substance that had no Midas touch, but did glow in the dark, prompting Brandt to baptize the phosphorus, Greek for ‘bringer of light’.
This pure form of the element, called white phosphorus, was found to be poisonous and flammable, so it has been used in warfare, to make rail bullets, smoke screens, and the Allied incendiary bombs that devastated Brandt’s hometown during World War II.
White phosphorus also shot to stark Dickensian fame in the 1800s, when it was added to the tops of matchsticks to produce “strike everywhere” matches. The girls and women who toiled in poorly ventilated factories producing the hugely popular product were sometimes exposed to so much phosphorus vapor that they contracted “phossy jaw,” a horrific condition in which their gums receded, their teeth fell out and their jawbones dissolved. According to historian Louise Raw, matchmakers’ fight for safer working conditions has fueled the modern union movement.
Pure phosphorus does not exist in nature, but is instead linked with oxygen, like phosphate, and this molecular union, the phosphorus-oxygen bond, “is at the heart of why biology works,” Matthew Powner, an organic chemist at University College London, said. The body stores and burns energy by constantly making and breaking the phosphate bonds found in the cell’s tiny ATMs, the adenosine triphosphate molecules, more commonly known as ATP. The phosphate recycling operation is so brutal, said Dr. Powner, “You actually turn your body weight into ATP every day.”
Phosphate bonds with sugar to form the backbone of DNA, holding the letters of genetic information in a meaningful order that would otherwise collapse into alphabet soup. Phosphate works in tandem with lipid molecules to envelop each cell in an ever-vigilant membrane that dictates what comes in and what should be kept out. Proteins send messages to each other by exchanging phosphate packets.
Behind the spectacular jack-of-all-trades phosphate utility is a negative charge that prevents unwanted leakage. “You can put energy in and take it out only if you want to,” said Dr. Powner. “It won’t leach into the environment.” By contrast, he said, the equivalent carbon-based molecule, called carbonate, dissolves easily in water: “If you attached DNA together with carbonate instead of phosphate, it would all fall apart.” dr. Powner has joked that we should consider life phosphate rather than carbon.
But unlike the other important ingredients of life – carbon, nitrogen, oxygen, hydrogen – phosphate molecules do not have a gas phase. “They’re too big to fly,” Dr. Sella said. Phosphates jump into the game of life through the erosion of rocks, the breakdown of living organisms, or waste products such as urine or guano. Understanding the impact of phosphate fluxes over time is an important research effort.
A lingering mystery is how early life got its hands on phosphate in the first place. Given how essential phosphate is to every aspect of biology, the original aqueous environment in which the first cells arose must have been rich in phosphate. “Yet most of the natural waters on Earth today are quite poor in terms of phosphate,” said Nicholas Tosca, a geochemist at the University of Cambridge. “We expected the same to be true for early Earth.” Iron, he explained, was thought to lock up the phosphates.
dr. Tosca and his colleagues in Cambridge tackled the riddle of the origin of life in a study recently published in Nature Communications. The researchers decided to reconsider the assumption and asked: What was it like in the beginning, when there was much less oxygen around? Oxygen, they knew, turns iron into a form that pots stubborn phosphate. What would happen if oxygen were removed from the equation? The researchers created artificial seawater in a large oxygen-free glove box and found that under those conditions, the dissolved iron left most of the phosphate alone, presumably available to any protocells nearby.
In the Trends in Ecology and Evolution article, Dr. Kraft similarly argued that the Cambrian seas were relatively overcrowded with phosphates. In fact, animals could absorb so much that they could make thick and durable shells, as hard as the hardest tissue in the human body – the phosphatic enamel of our teeth.
“It’s a big advantage to have these shells,” said Dr. power. In comparison, the shell of a modern mollusk, made of calcium carbonate, easily cracks under the feet of a beachcomber. But as the seas filled up and bony fish appeared, phosphate reserves dwindled and brachiopods could no longer freely gather what they needed to build their expensive homes. Bony fish were wise in their use of phosphate as a building material: their teeth, a few parts of the skeleton, and that was it. And because they are mobile, fish were able to capture all the phosphate and other nutrients filtered from land to sea before reaching the unwieldy hard shells below.
The vertebrates had seized control of phosphate and nothing could stop them now.
#sad #fate #wellarmed #sailors