Neil Comins, a University of Maine astronomer, talks Wednesday at a Great Falls Forum held online. Screenshot from video

When the Earth was still a fresh-faced youngster in a spanking new solar system some 4.6 billion years ago, it rotated so quickly that its days lasted only about eight hours.

And the moon that spun around it was perhaps 10 times as close as it is today, creating sea tides perhaps a thousand times higher than they are now, washing tons of debris into the water and creating the conditions for life to arise.

In all the years since, said Neil Comins, an astronomer at the University of Maine, the Earth’s rotation has been slowing down, the tides growing less fierce and the moon slowly spiraling away from the big blue orb that spawned it long ago.

Speaking at an online version of the Great Falls Forum on Wednesday, Comins explored a question that’s intrigued him for three decades: What if the moon didn’t exist?

The short answer is that without the moon, no creature on Earth would be asking questions about anything. Any life that did exist would be far more primitive and quite different than what ultimately arose, Comins said.

That the Earth has a moon is a consequence of what was surely the most devastating day in the planet’s history.

An artist’s rendering released by NASA shows what a planetary collision near the star Vega might look like. It’s similar to what happened on earth to create the moon, he said. NASA photo

Comins said a Mars-sized object clobbered the planet, splashing an enormous amount of debris into orbit, creating a spinning disc of dust and rocks that eventually “started clumping together” to form the moon.

That collision knocked the Earth so hard that it caused the entire planet to tilt on its axis, a development that might not seem like a big deal to some — but it is.

Remove it from history and Earth would have no seasons, Comins said, because the sun would rise and set in the same place day after day, with half of each day dark and half of it light.

But the impact of not having a moon would be even more drastic.

Comins said that the Earth and moon revolving at different rates around a point 1,064 miles beneath the terrestrial surface — it’s a misconception that the moon simply revolves around the planet that spawned it — makes for changing tides across the globe.

Those high tides, spurred mostly by the moon’s gravity, have the effect of both slowing the earth’s rotation while simultaneously “causing the moon to spiral away” about 1.5 inches annually, Comins said.

Don’t worry about the moon escaping, though, since that will take about 15 billion years “but the sun is going to die about 7 or 8 billion years from now,” Comins said, making the moon’s presence a moot point.

This view from the Apollo 11 spacecraft in 1969 shows the Earth rising above the moon’s horizon. NASA/JSC

If the moon had never been around at all, he said, winds on the earth’s surface would be “significantly stronger” because of its faster rotation, and the shorter days. Tall trees would never stand a chance.

The biological clocks that earthbound animals rely on would be entirely different, Comins said, presumably resulting in life that may be quite different than what has actually evolved with the moon overhead.

Without those huge tides from a closer moon in its early days, the process of getting life underway at all would likely have taken far longer in any case, he said.

The moon gave us “a more tranquil world,” he said, and one suited to the plants and animals that arose.

Comins, who has been in Orono since 1978 and written 21 books, urged those listening to his talk to cherish the Earth.

“We humans have the potential to make the world a better place by taking care of it and preventing bad things from happening,” he said.

His talk is slated to be viewable on the library’s YouTube page starting Thursday.

The Great Falls Forum brings statewide and regional leaders in public policy, business, academia and the arts to the Lewiston Public Library each month, normally for brown bag lunches.

The free forum is sponsored by the Sun Journal, Bates College and the library.

Its next speaker, who is scheduled to appear via Zoom online at noon on Oct. 15, is Emmanuel Kayembe, Fellow for Franco-American Studies at the University of Southern Maine. He will talk about “Francophonie, Immigration, Cultural Diversity and Intercultural Identities in the USA.”

Neil Comins, an astronomer at the University of Maine, left, speaks during Wednesday’s Great Falls Forum talk. Marcela Peres from Lewiston Public Library is at right. Screenshot from video