WASHINGTON (AFP) - Americans' knowledge of basic scientific facts is just average, says a poll out on Thursday that also revealed differences by education level, gender, race and age.
Among 3,200 adults tested, the median score out of 12 questions was eight correct, says the survey by the Pew Research Centre.
Some 27 per cent answered eight or nine questions correctly. Another 26 per cent got 10 or 11 right, and just 6 per cent got them all right.
Seventy-three per cent knew the difference between astronomy and astrology.
A total of 86 per cent correctly identified the Earth's inner layer, or core, as its hottest part. And 82 per cent knew uranium is needed to make nuclear energy and nuclear weapons.
Seventy-four per cent of those surveyed identified Jonas Salk as the man who developed the polio vaccine. They chose from a pool that included Marie Curie, Albert Einstein and Isaac Newton.
Americans did less well on other questions, however.
For instance, only 35 answered correctly that the property of a sound wave that determines loudness is the amplitude, or height, of that wave.
And only 34 per cent knew that the temperature at which water boils - which is linked to atmospheric pressure - is lower at a higher altitude setting than at sea level.
Unsurprisingly, Americans with higher education levels did better on the test.
A total of 57 per cent of adults with a postgraduate degree got 10 to 12 correct answers, compared to 18 per cent for those with a high school diploma or less.
As for gender, men averaged 8.6 out of 12 correct answers, while for women it was 7.3.
Some 24 per cent of women answered 10 or more questions correctly. For men it was 43 per cent.
Whites, with 8.4 correct answers out of 12, did better than Hispanics (7.1) and blacks (5.9).
Younger adults - aged 18 to 49 - generally had more scientific knowledge than older ones (65 or older). The latter averaged 7.6 correct answers out of 12, while the younger adults averaged eight or more correct answers.
A 2014 poll by the National Science Foundation had already shown that science is not the strong suit of many Americans: 25 per cent did not know the Earth revolves around the sun.