Radioactive Decay and Absolute Dating - ppt download
be achieved after the development of radiometric dating in the 20th century. . dykes －sheet-like intrusion intersecting rock layers－), faults, and unconformities can Based on this method, an American geochemist named Clair C. Patterson . The process of dating rock layers is very difficult. One method used to determine the absolute age of some rocks is radioactive dating. A radioactive date. Students can complete this worksheet while watching Cosmos: Episode topics (like geology and radiometric dating) as well as good lab technique What kind of crystals did Harrison Brown ask Clare Patterson to work on?.
In the brain, calcium ions bounce between neurons to help keep the synapses firing. But when the body absorbs lead, the toxic metal swoops in, replaces calcium, and starts doing these jobs terribly—if at all. The consequences can be terrifying. Neurotransmitters, the chemical paperboys of the brain, stop delivering messages and start murdering nerve cells.
It also weakens the blood-brain barrier, a protective liner in your skull that blocks microscopic villains from infiltrating the brain, the result of which can lower IQs and even cause death. Lead poisoning is rarely caught in time. Poisoning from pure tetraethyl leadhowever, works differently.
Just a few teaspoons directly applied to the skin can kill. After soaking the dermis, it leaches into the brain, and, within weeks, causes symptoms similar to rabies: Midgley would recover, but the same could not be said for his employees. During the spring oftwo workers in Dayton, Ohio, died under his watch. Dozens more went insane. Midgley knew the men and, freighted with guilt, sank into depression and pondered removing leaded gasoline from the market.
Kettering coaxed him out of it. Instead, he hired a young man named Robert Kehoe to make the toxin safer in factories. Whip-smart and reticent, Kehoe was a young assistant professor of pathology at the University of Cincinnati.
The new gig would change his life. He met about 20 injured workers and concluded that heavy lead fumes had sunk to the factory floor and poisoned the men. Just install fans in the factory. With that, business resumed. Then came the tragedy at Bayway, New Jersey. A advertisement in Life magazine for Ethyl leaded gasoline.
Henderson worried about car exhaust. Tailpipes burped lead dust into the air pedestrians and residents breathed. Every gallons of gas emitted a pound of toxins into the air. It had commissioned a study that exposed pigs, rabbits, guinea pigs, dogs, and monkeys to leaded engine fumes every day for eight months. No signs of lead poisoning were found. A dog did have five puppies. The study was flawed. As a PR precaution, the Ethyl Corporation suspended sales of leaded gasoline and held its breath.
Lead companies simply had to make factories safer for their workers. Months later, a committee appeared to agree. Signs hanging above roadside service stations in rang in the news: But it never happened. In fact, independent researchers failed to study leaded gasoline for the next four decades. For plus years, the safety of leaded gasoline was studied almost entirely by Kehoe and his assistants. Kehoe and the Ethyl Corporation would maintain this monopoly until Clair Patterson, scratching his head in a Chicago laboratory, wondered why so much lead was fouling his beloved rocks.
Clair Patterson went to great lengths to keep lead and other contaminants out of his laboratory. As journalist Lydia Denworth describes in her book, Toxic TruthPatterson went to enormous lengths to rid his lab of contaminants. He bought Pyrex glassware, scoured it, dunked it in hot baths of potassium hydroxide, and rinsed it with double-distilled water. He mopped and vacuumed, dropping to his hands and knees to buff out any traces of lead from the floor.
He wore a mask and gown and would later cloak his body in plastic. The intensity of these measures was unusual for the time. Five years would pass before Patterson finally perfected his own ultraclean techniques.
Inhe managed to prepare a totally uncontaminated lead sample and confirmed the age of a billion-year-old hunk of granite, an accomplishment that earned him a Ph. The next step was to use the same procedure to find the age of the Earth. Funding was all that stood in his way. Patterson applied for a grant through the U.
Atomic Energy Commission, but the AEC rejected the proposal, prompting Harrison Brown to step in and rewrite it, inflating the language to make false—but profitable—promises: Patterson's work, he claimed, could help the commission develop uranium fuel. Patterson got the money, and he eventually followed Brown west to start a new job at the California Institute of Technology.
At Caltech, Patterson built the cleanest laboratory in the world. He tore out lead pipes in the geology building and re-wired the walls lead solder coated the old wires. He installed an airflow system to pump in purified, pressurized air and built separate rooms for grinding rocks, washing samples, purifying water, and analysis. The geology department funded the overhaul by selling its fossil collection.
Patterson knighted himself the kingpin of clean. The lead from your hair, when you walk into a super-clean laboratory like mine, will contaminate the whole damn laboratory. Just from your hair. As Patterson prepared the sample that would help him find the age of the Earth, he became increasingly prickly. He demanded that his assistants scrub the floor with small wipes daily. When the sample was ready, Patterson traveled to the Argonne National Laboratory to use their mass spectrometer.
Late one night, the machine spat out numbers. The Earth was 4. Overcome with glee, Patterson sped to his parents' home in Iowa. Instead of cutting a cake in celebration, his parents rushed him to the emergency room, convinced their overexcited son was having a heart attack.
Each time they tried to prove it wrong, they failed. Lead contamination, he learned, was ubiquitous, and nobody else knew it. He was clueless as to where the lead originated. All he knew was that every scientist in the world studying the metal—from the lead in space rocks to the lead in a human body—must be publishing bad numbers.
That included Robert Kehoe. Robert Kehoe in the s. Winkler Center for the History of the Health Professions, University of Cincinnati Libraries After the two deaths in Dayton inKehoe became one of the first people in the chemical industry to propose standard workplace safety measures. He stressed that employees needed to be trained before they handled dangerous chemicals.
He vouched for improving the ventilation in plants. He tracked the health of workers. He saved lives, and ultimately, the profits to be made off leaded gasoline.
After the disaster in New Jersey, as critics questioned the safety of car exhaust, Kehoe scoffed. This was an issue—his client, DuPont, made benzidine. But rather than alert American workers to the risk, Kehoe stuffed the report in a box. Kehoe also understood the dangers of lead paint. In one study, Kehoe measured the blood of factory workers who regularly handled tetraethyl lead and those who did not.
Blood-lead levels were high in both groups. This mistake would grow into an unshakeable industry talking point. Kehoe's research also led him to wrongly believe that a quantifiable threshold for lead poisoning existed. At risk, but fine. You can be barely poisoned, slightly poisoned, mildly poisoned, moderately poisoned, significantly poisoned, extremely poisoned, fatally poisoned. Kehoe was held in such high esteem, the journal Archives of Environmental Health dedicated an issue in his honor.
And he had lead all wrong. After determining the age of the Earth inPatterson set out to answer a new riddle: He knew studying lead in ocean sediments could provide the answer, so he aimed his sights on the sea. He had pitched the idea to the petroleum industry with the false promise that drilling for ancient sand could benefit oil companies.
Patterson knew that if he compared the lead levels in shallow and deep water, he could calculate how oceanic lead has changed over time. The same strategy applied to sediment. Sand resting atop the seafloor is relatively new, but sediment buried 40 feet below is older. Patterson collected samples from all depths and returned to his ultraclean lab. He found that the samples of young water contained about 20 times more lead.
This was not normal. Mining the literature for an explanation, Patterson stumbled on data about leaded gasoline. Then he published the numbers anyway. Quotation from Geochimica et Cosmochimica Acta, But the minute he published a paper in Nature blaming the industry for abnormal lead concentrations in snow and sea water, the American Petroleum Institute rescinded its funding. Then his contract with the Public Health Service dissolved.
At Caltech, a member of the board of trustees—an oil executive whose company peddled tetraethyl lead—called the university president and demanded they shut Patterson up. One day, the petroleum industry knocked on Patterson's door. I explained how this information would be used in the future to shut down their operations. Later, Patterson would learn that the industry had asked the Atomic Energy Commission to stop subsidizing his work. Denworth's book Toxic Truth details how the industry attempted to paint Patterson as a nutjob—which, in fairness, was not difficult.
He went distance running when distance running was a hobby for weirdos. He wore t-shirts, khakis, and desert boots. Later in his career, he soundproofed his Caltech office and installed two doors, two layers of walls, and two ceilings. As his colleague Thomas Church noted, Patterson was like his rock samples: He did not enjoy being "contaminated" by outside influences. Patterson submitted an essay singed with fire and brimstone that listed all of the possible natural causes for the lead surge: He showed his math and explained bluntly that these phenomena could not explain the lead boom.
His conclusion was dire. The human body probably contained times more lead than natural. Kehoe was asked to peer-review the paper.
Clair Cameron Patterson
Patterson's entire line of reasoning was laughable. He was a geologist and a physicist. What did he know about biology? The overarching tenor was stick to rocks and leave the human body to the experts. Let us hope that this article will prove to be the first and the last on science fiction. His saving grace was a blend of old fashioned stubbornness and a hearty conviction that science, whether accepted by the majority or not, was a gateway to truth.
The only way to win over skeptics, he figured, was to do more research. In the s, Patterson visited Camp Century, an underground research center in Greenland, to take ice samples.
The camp looked sleepy from the air. A blanket of snow littered with oil drums and caterpillar tractors. But about 20 feet below the ice sheet, hundreds of soldiers buzzed in a labyrinth of tunnels that included, along with a theater, library, and post office, several secret annexes. Patterson was through with bombs. He came to dig for giant ice cubes. In the arctic, snow acts like sediment. Old snow rests deep under your feet while younger snow settles on top of it.
Anyone who digs deep enough can effectively dig back in time. Patterson wanted to compare the lead in ancient ice to new ice and needed to excavate about gallons of it. At this depth, the snow was years old.
The crew wore suits and gloves cleaned in acid. Using acid-washed saws, they slowly cut 2-foot cubes of ice, placed them in giant acid-washed plastic containers, and lugged them out of the tunnel to a plastic-lined trailer at the surface. The ice was melted, placed on military cargo planes, and flown to a lab in California. While the base was excellent for dredging up ancient ice—they collected samples as old as years—the surface was too polluted.
So, to find pristine new deposits of ice, Patterson and a group of soldiers crammed into three snow tractors and plowed through a storm. Cascades of snow gobbled the sun, and Patterson, who fruitlessly attempted to navigate with a sun compass, had to mark their tracks by stopping and planting a flag every couple feet.
After reaching a desolate snowy plain, they dug a trench 50 feet deep and feet long. A year later, Patterson relived the episode in Antarctica. With summer temperatures dipping to 10 degrees below zero, his team, shrouded in clear plastic suits, revved electric chain saws and dug tunnels into the snow, feet long and feet deep. They gathered samples from 10 distinct eras. As one member later recalled in Toxic Truth, "It drove Pat nuts that everybody's nose dripped, as it does in the cold.
The worry was an unnoticed drip would fall on a block. If your nose did drip, we would take tools and chip a few inches around the spot where it fell. It could take days to analyze just one sample. He made researchers wrap their bodies in acid-washed polyethylene bags. Each new sample was handled with a new pair of acid-cleaned gloves. Years later, when Patterson analyzed more ice cores from Antarctica, he pointed to a spot on an ice sample and told his assistant, Russ Flegal, it was older than Jesus.
But the most startling jump had occurred in the last three decades. Talk about smoking guns: Lead contamination had rocketed as car ownership—and gasoline consumption—boomed in North America.
By more than percent. Patterson received a bigger surprise, however, when he surveyed the oldest ice samples. Neither was ice from the year BCE. Lead pollution was as old as civilization itself. Graph as represented in Clean Hands. The great periods of early human progress, stretching from Neolithic times to the advent of writing, are named for metals, the ores that ancient people used to make tools, weapons, pottery, and currency—the glinting sparks of civilization.
Humans have relied on it for millennia. About years ago, humans discovered they could extract silver by smelting lead from sulfide ores.
Ancient Mesopotamians and Egyptians, and, later, the Chinese used lead to toughen glass. From the Babylonians onward, people glazed pottery with lead.
With its low melting point, the soft and malleable metal was a metallurgy miracle. Lead was a to-1 byproduct of silver during the heydays of Grecian mining. Between BCE and the height of Roman power, around year 0, humans produced 80, tons of lead a year.
Working hour days, Roman slave miners dug pits up to feet deep and extracted the metal by setting seams of rock ablaze. Pliny suspected the smoke ravaged their lungs: In fact, the Eternal City became so swamped in the metal that it forbade the use of lead as currency.
Lead pipes connected Roman homes, baths, and towns with a glorious network of water. According to Lloyd B. The Roman architect Vitruvius begged officials to use terracotta instead. And then it collapsed. Inthe Pope banned the practice of adulterating wine with lead.
The decree was largely symbolic.
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At that point, lead was pervasive. It was even in cosmetics. Intellectuals continued ringing alarms, but nobody took heed. Instead, entire buildings were constructed devoted to the production of lead. European skylines were punctuated by shot towers, where molten lead slithered down ramps to form bullets. In lead-loving New England, infant mortality and stillbirths were 50 percent more common than locales that used another metal.
People knew lead was responsible. In England, a pathologist named Arthur Hall recommended that any woman who needed an abortion should just drink the tap water. On the black market, lead was the main ingredient in abortion pills.
In the 20th century, lead paint was marketed as a replacement for wallpaper. The Dutch Boy Paint Company, the dominant lead paint manufacturer, targeted children by selling paint coloring books with jingles: Therefore, if any lead is present in the zircon, it must come from the decay of uranium.
This process is known as U-Pb dating. The job of the team was to measure the concentration and isotopic compositions of the elements inside the zircon.
Tilton was to measure the uranium and Patterson, the amount and type of lead.
Radioactive Decay and Absolute Dating
In doing so, it would be possible to figure out the age of the solar system and, in turn, the Earth from using the same techniques on meteorites. As Patterson and Tilton began their work inPatterson quickly became aware that his lead samples were being contaminated. They knew the age of the igneous rock from which the zircon came, and Tilton's uranium measurements aligned with what should be in a zircon at that particular age, but Patterson's data always was skewed with too much lead.
Brown was able to receive a grant from the United States Atomic Energy Commission to continue work on dating the Earth, but more importantly, to commission a new mass spectrometer in Pasadena, California at Caltech. InBrown brought Patterson along with him to Caltech, where Patterson was able to build his own lab from scratch.
In it he secured all points of entry for air and other contaminants. Patterson also acid cleaned all apparatuses and even distilled all of his chemicals shipped to him. In essence, he created one of the first clean rooms ever, in order to prevent lead contamination of his data.
He used the mass spectrometer at the Argonne National Laboratory on isolated iron-meteorite lead to collect data on the abundance of lead isotopes.
Deriving from the different ages at which the landmasses had drained into the ocean, he was able to show that the amount of anthropogenic lead presently dispersed into the environment was about 80 times the amount being deposited in the ocean sediments previously: The limitations of the analytic procedures led to his use of other approaches. He found that deep ocean water contained up to 20 times less lead than surface water,  in contrast to similar metals such as barium.
That led him to doubt the commonly held view that lead concentrations had grown by only a factor of two over naturally occurring levels. Patterson returned to the problem of his initial experiment and the contamination he had found in the blanks used for sampling.
He determined, through ice-core samples from Greenland taken in and from Antarctica inthat atmospheric lead levels had begun to increase steadily and dangerously soon after tetraethyl lead began to see widespread use in fuel, when it was discovered to reduce engine knock in internal combustion engines.