Perseverance's SuperCam laser found strong, narrow glows at 692.7 and 694.1 nanometres in a light-coloured rock, and timing the delay of the light showed it came from chromium atoms in the mineral corundum. Gem-quality chromium-bearing corundum is ruby: before launch the team put a ruby in the laser beam and the whole room pulsed red. No collectable rubies have been found, but the tiny corundum crystals are informative. Corundum is a metamorphic mineral that Mars, with no plate tectonics, would not normally be expected to make. Large impacts can heat rock for a long time and cause local metamorphism, which fits the ancient terrain near Jezero crater's rim.
how it works
When a laser strikes chromium atoms in corundum, they absorb energy and re-emit it as red light after a short delay. SuperCam measures that delay, which separates this glow from other kinds of light.
so what
The finding gives geologists a new way to spot rocks that were cooked by ancient impacts. The team now routinely checks light-toned rocks for this glow.
fun fact
Sapphires and rubies are both corundum; the red colour of ruby comes from traces of chromium.
In 1909 D. W. Griffith made a 14-minute film about a speculator who corners the wheat market and doubles the price of bread. A farmer sows his field while a 'Wheat King' gambles in the Chicago wheat pit; bakers raise the loaf from five cents to ten and the poor line up for bread. Griffith cut back and forth between the farm, the feast and the breadline, a technique called parallel editing, so audiences saw both ends of the economy at once. The film drew on Frank Norris's stories and on a real scheme: months earlier Chicago financier James Patten had cornered wheat, sent bread prices up and made about $5 million, roughly $185 million today.
how it works
To corner a market, a trader buys up most of the available supply and the futures contracts that promise more. Anyone who has to deliver the commodity must then buy from the cornerer at whatever price is demanded. The trader profits until the stock is released or the scheme collapses.
so what
A century on, it still shows how markets can be rigged by someone who controls supply, and how the people at either end, farmers and eaters, pay for it. It also helped establish editing as a way to argue a point, not just tell a story.
the bigger pattern
Corners have recurred whenever supply could be locked up, from the Hunt brothers' attempt on silver in 1979 to 1980 to the 'Black Friday' gold panic of 1869. Many such schemes end by collapsing, and the response is often new rules on speculation.
fun fact
In the film the Wheat King dies by falling into a grain elevator and being buried in the wheat he hoarded, an ending borrowed from Norris's novel The Octopus.
more on this
background
A Corner in Wheat is a 1909 American short silent film which tells of a greedy tycoon who tries to corner the market in wheat, destroying the lives of the people who can no longer afford to buy bread. It was directed by D. W. Griffith and adapted by Griffith and Frank E. Woods from a novel and a short story by Frank Norris, titled The Pit and "A Deal in Wheat". Griffith may have had a real-life inspiration: six months earlier, James A. Patten had actually cornered the market in wheat, and in some cities, the price of bread doubled from five cents to ten, just as in the movie.
In 1994, A Corner in Wheat was selected for preservation in the United States National Film Registry by the Library of Congress as being "culturally, historically, or aesthetically significant".
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7.30 host Sarah Ferguson speaks to Usman Khawaja.
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