For some years beginning in the 1990s, it became trendy for scientists and the public to jump on the bandwagon of the idea that comets supplied huge amounts of water to early Earth. Conferences included considerable talk about the notion. Writers pounded out books suggesting the idea was ironclad. Several studies cropped up adding apparent weight to the evidence that much or most of Earth’s water — and the conditions friendly to abundant life — rained down from outside the atmosphere when Earth was in its formative years.
You can read the real story on what’s known about comets contributing water to early Earth on my latest Huffington Post blog.