November 15, 2023: Dark energy's 25th anniversary, plate tectonics' 4 billionth or so anniversary and letting students use and then grade AI to see its faults. —Robin Lloyd, Contributing Editor | | | "Dark Energy" Anniversary | This year marks the 25th anniversary of the discovery of evidence for "dark energy"—a moniker for whatever is driving the acceleration of the universe. Today, scientists are still trying to figure out what it is, writes Richard Panek. In the late 1980s and early 1990s, cosmologists started to update graphs showing two values: the velocities with which galaxies are apparently moving away from us on one axis and the distances of the galaxies from us on the other. The original diagram, made by astronomer Edwin Hubble in the 1920s, had indicated a straight-line correlation between a star's distance from Earth and its velocity. As the new data came in, astronomers were shocked to see that the universe seemed not to be expanding steadily or slowing down, as expected —its expansion was actually speeding up.
How they did it: From 1994 to 1997 two groups of scientists collected powerful telescope data on dozens of supernovae that allowed them to extend the Hubble diagram farther and farther. If the universe's expansion was decelerating, at some point that line would have to deviate from its 45-degree slope, bending downward to indicate that distant objects were brighter and therefore nearer than one might otherwise expect. By the first week of 1998 both teams of scientists found evidence that the line indeed diverged from 45 degrees. But instead of curving down, the line was curving up, indicating that the supernovae were dimmer than they expected and that the expansion therefore wasn't decelerating but accelerating. The unknown energy driving that acceleration is what is known as dark energy.
What's next: Over the decades observers have gathered ever more convincing evidence of dark energy's existence, and this effort continues to compel a significant part of observational cosmology while inspiring ever more ingenious methods to define it. | | | Early plate tectonics created the oldest rocks on Earth, which are about four billion years old—just short of the planet's age of 4.5 billion years, a recent experimental study suggests. The finding counters computer models which suggest that plate tectonics began three billion years ago or less. Field geologists, however, often point to four-billion-year-old rocks in places such as Canada and Australia as evidence of an earlier start. These ancient rocks appear to have been made by subduction, when two plates collide to thrust one of them deep into Earth's mantle.
How they did it: The researchers set out to test whether some of these oldest rocks could have been created at shallower, nonsubduction depths. Samples of oceanic crust in the southwestern Pacific, which has a composition similar to Earth's first continental crust, were subjected to high pressures and temperatures to simulate the environment in which they might have formed without subduction, in the upper 50 kilometers of the crust.
The finding: The researchers found that this environment couldn't produce samples with the same mineral makeup as the four-billion-year-old rocks. Rocks formed under different pressures and temperatures are composed of different minerals, so this mismatch between the new and ancient samples indicated that the ancient rocks had formed farther—more than 50 kilometers—down. Subduction is the only known process that could push so deep. | | | • Viruses can prey on other viruses to replicate themselves and may hold the key to new antiviral therapies. | 14 min read | | | • As a surging blob of magma under an Iceland peninsula threatens to erupt, it is causing earthquake swarms and forcing evacuations. | 4 min read | | | • Teachers and professors might be tempted to ban ChatGPT from classrooms. But an Elon University faculty member, C.W. Howell, writes that he took an alternative approach. For a class assignment, each student was required to generate their own essay from ChatGPT and then "grade" it according to Howell's instructions. The results were eye-opening: Every one of the 63 essays contained confabulations and errors. The exercise effectively taught students, two of whom also shared their insights on AI in education in the essay, about the flaws in models like ChatGPT. | 5 min read | | | • At SpaceX, worker injuries soar in Elon Musk's rush to Mars.| Reuters | | | • Insurance companies have responded to climate disasters by raising premiums and dropping customers. Now there's a new housing bubble waiting to burst. | The New York Review | | | • The hidden power of China's pandas—and why the U.S. is losing them all. | The Washington Post | | | • The man who invented fifteen hundred necktie knots. | The New Yorker | | | Earth's climate emergency is front and center in my mind most days, but I also am on the lookout for positive climate news. Today, China and the U.S., the two biggest carbon polluters in the world, agreed "to reduce planet-warming emissions from the power sector this decade and committed for the first time to curb all greenhouse gases," according to a ClimateWire story we republished this afternoon. It's a pretty big deal, particularly in light of tense relations between the two nations for several years, I was told today by Andrea Thompson, our associate editor covering the environment, energy and earth science. For other positive climate news, check out the Facebook page "Not Too Late" and clean-energy entrepreneur Assaad Razzouk on X. I also follow climate scientist Katharine Hayhoe's work. She writes regularly for Scientific American, and you can subscribe to her newsletter or follow her on Facebook, YouTube or X. As journalist Rebecca Solnit recently wrote: "Fighting defeatism is also climate work."
| If you have any feedback, suggestions, or spot any errors while reading these newsletters, please reach out to us. | —Robin Lloyd, Contributing Editor | | Subscribe to this and all of our newsletters . | | | | Scientific American
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