Creation Moment 2/21/2018 - Death of a Myth

"A favorite tale from the Apollo era, the so-called Late Heavy Bombardment, is being bombarded itself.

It was a nice story while it lasted. It explained craters on the moon and the timing of life on the earth. It gave TV animators something to do. But it never happened. At Nature, Adam Mann writes that “New analyses undermine a popular theory about an intense asteroid storm 4 billion years ago.”  First, he recounts the old myth:

Early in Earth’s history, roughly half a billion years after the planet formed, all hell broke loose in the inner Solar System. A barrage of asteroids — some the size of Hong Kong — pummelled the globe intensely enough to melt large parts of its surface. This incendiary spree around 4 billion years ago vaporized most of Earth’s water and perhaps even sterilized its exterior, killing off any life that might have started to emerge. Only after this storm of impacts passed did the planet become safe enough for hardy

organisms to take firm root and eventually give rise to all later life.

What happened to this story that has been repeated since the 1970s? Increasing numbers of geophysicists are calling the LHB fake science.

That horrific episode, known as the Late Heavy Bombardment (LHB), has been an integral part of Earth’s origin story for decades, ever since geologists did a systematic study of samples brought back from the Moon by NASA Apollo missions. But now, the once-popular theory has come under attack, and mounting evidence is causing many researchers to abandon it.

The reason that moon rocks were used to fortify the LHB is that earth rocks have been recycled by plate tectonics, he says. The moon, though, was supposed to preserve a pristine record of early solar system history.

What happened? The LHB myth began when Caltech scientists measured the same radiometric date, 3.96 billion years, in moon rocks from four widely separated sites. Using scientific divination, they envisioned a flurry of impacts all around the same time, giving it the name Late Heavy Bombardment. But not everyone liked the story. “The idea was immediately divisive,” Mann says, “in large part because of ambiguity in the rock dating.”

What would cause a flurry of asteroids to strike the inner solar system after things should have settled down? In 2005, another idea, the “Nice model” (named after the city of Nice in France where it was conceived), proposed that interactions of Jupiter with the Kuiper Belt might have sent objects in to create the LHB. Most planetary scientists accepted this as the source of the unusual bombardment. 

The story began to unravel in 2009, when planetologists began to suspect that all the Apollo samples with the same date had come from Mare Imbrium. Crater count dating and re-analysis of radiometric dates began to spread the ages, not indicating a spike at 3.96 billion years. Mark Harrison may have said too much:

Others are still scrutinizing the original Apollo evidence. To determine the samples’ ages, researchers heated the rocks to release argon, slowly ramping up the temperature. But as far back as 1991, Harrison had pointed out that the process won’t work well for rocks containing multiple minerals. Different minerals will release their argon at different temperatures. A sample heated to 400 °C might provide an age of 2 billion years; to 500 °C, an age of 2.5 billion. Researchers have tried to extrapolate from this behaviour, but Harrison says the complex patterns often lead them to pick essentially

arbitrary ages. “This is quackery,” he says. “There’s no physical basis for it.”

Others disagree, so it has taken awhile for the myth of the LHB to evaporate.

Such back and forth underscores how difficult it can be to tease small clues out of extremely ancient rocks. “Sherlock Holmes was good at resolving mysteries that happened last year,” says David Nesvorný, a planetary scientist at the Southwest Research Institute in Boulder, Colorado. “This all happened 4 billion years ago.”

Meanwhile, the Nice Model, that seemed to clinch the LHB, has come under attack as well. Modelers are realizing that getting a late bombardment to work is like trying to balance a pencil on its tip, Mann writes. One of the architects of the Nice Model now “admits that the first versions took fine-tuning to get the reshuffling to occur so late.” He now predicts that the LHB idea will be abandoned, after the last holdouts change their minds.
How could astronomers be so wrong?

This is an important article for a number of reasons.
*One issue concerns radiometric dating. The public is taught that it is infallible, but we see the scientists themselves disputing the results and pointing out sources of error in interpretation.
*Another issue is the sociology of science: these guys commit intellectual inbreeding inside their cliques. Sure, they may disagree about details, but they drink beer together and all know each other. How likely are they to think totally outside the box?" CEH

But thou, O LORD, shalt laugh at them;
Psalm 59:8