Scars on the surface of the Moon record a hail of impacts during what is called the Late Heavy Bombardment. The Earth would have received an even more intense bombardment, and the common thinking until recently was that life could not have emerged on Earth until the bombardment eased about 3.85 billion years ago.
Norman H. Sleep, a professor of geophysics at Stanford, recalled that in 1986 he submitted a paper that calculated the probability of life surviving one of the giant, early impacts. It was summarily rejected because a reviewer said that obviously nothing could have lived then.
That is no longer thought to be true.
"We thought we knew something we didn't," said T. Mark Harrison, a professor of geochemistry at the University of California, Los Angeles. In hindsight the evidence was just not there. And new evidence has suggested a new view of the early Earth.
This, of course, is how science actually works. All scientific knowledge is tentative, subject to constant challenge by new hypotheses and new evidence.
Keep this in mind every time a global warmist claims that the "scientific consensus" about "climate change" is unchallengeable.
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