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Americans don’t know a lot about the universe but they’re sure it is so complex it had to be created by a god. That’s one possible reading of the latest AP poll where people were asked about their confidence in various scientific statements. 72% agreed at least “somewhat” that, “The universe is so complex, there must be a supreme being guiding its creation.” By contrast, “The Earth is 4.5 billion years old,” only received 60% support, and “The universe began 13.8 billion years ago with a big bang,” got only 46%.
As an article in The Atlantic points out, it is possible some people knew about the big bang but just weren’t confident about the 13.8 billion year figure. Polls in the past suggest that isn’t the case however. Some excerpts from the Atlantic article follow.Source: A Majority of Americans Still Aren't Sure About the Big Bang
Up until 2010, they asked the following question: True or false, the universe began with a huge explosion. Since 1990, the number of people answering true to that question has bounced between 32 and 38 percent. (The number was anomalously higher in 1988, a discrepancy that they do not explain.)
In 2012, the National Science Board tried to parse out why Americans were different by adding ‘according to astronomers’ into the Big Bang question for half the survey respondents. Like this:
According to astronomers, the universe began with a big explosion.
60 percent of Americans said this statement was true, versus 39 percent who said so when the “according to astronomers” was not present. This would suggest that 40 percent of people know the science, 40 percent of people don’t, and 20 percent have heard the science, but believe otherwise.
Before you lament the fall of the republic, consider that very little has changed in the public awareness of scientific knowledge over the past 20 years. The 2014 report put it bluntly: “The public’s level of factual knowledge about science has not changed much over the past two decades.”
The best resource in book form I have found that discusses how the age of the Earth is known is The Age of the Earth by Brent Dalrymple. It is a bit of a dry read but packed with info. There are also good summaries at Talk Origins the first being by Dalrymple himself.
It sounds like they used the Uranium-Lead concordia method (also described here), which takes advantage of the fact that there are two different ways Uranium decays into lead. One from U-238 to Pb-206 and another from U-235 to Pb-207. It is a particularly useful test because zircon doesn’t incorporate lead into its crystal at the time it forms.
The oldest remaining grain of early Earth’s original solid rock crust has now been confirmed to be a 4.374-billion-year-old old zircon crystal from Jack Hills, Australia.
That age should settle a scientific debate over the accuracy of that mineral’s internal clock, and cuts the time from when Earth was hit by a Mars-sized body (which led to the formation of the Moon) and the cooling and creation of Earth’s first solid crust from 600 million years to 100 million years.
The age of a grain is figured by measuring the amounts of the parent uranium isotopes compared to the daughter lead isotopes.