“Fit to be tide” (Early Earth tsunamis)

When the moon was in its earliest days, Earth and its satellite were closer to each other and orbited faster around one another. Our moon’s gravity controls the planet’s tides, so with the heavenly bodies being closer and spinning faster, there is a notion that all those years ago there were massive waves a mile high, regularly destroying and reshaping the landscape at tremendous speeds every day.

To see if this is real, Skeptoid’s Brian Dunning looked into the deep past, 4.5 billion years back, to a time when the solar system’s planets coalesced from the dust from leftover material from a dying star.

The remnants of what are today known as Theia and Gaia became our planet and moon. The two bodies would have stayed in the orbit they were in at the time for billions of years had it not been for Venus happening by and forcing Theia to wobble away. Disrupted from its Lagrange point, Theia plunged toward Gaia, drawn by its gravity, and the two stellar bodies collided.

When Theia slammed into Gaia, the resulting explosion coalesced into Earth. A ring likewise formed and this become the neophyte planet’s satellite. Earthly temperatures were extremely hot, to the point of having lava seas.

Tides cause oceans to move and this movement requires energy, which is taken from the bodies’ rotation speeds. This causes the two bodies to become tidally locked, meaning the same sides face one another. Our Moon is already tidally locked with Earth, and eventually Earth will also become tidally locked with the moon.

When trying to figure out how far away the moon was at some point in time, Dunning writes that there are clues from Earth’s geologic record. Sedimentary rock layers record rhythmic events, including some tidal cycles. This enables geologists to determine annual tide intensity. They know that by the time Earth had liquid oceans, the Moon sat 80 percent as far away as it is now. This would cause a tidal force of about 40 percent greater than today.

But since the intensity of tides varies, this increase is less than today’s normal range. While tides were larger overall, in most places they were still less than the swings experienced today. Dunning wrote, “There were never vast walls of whitewater crashing across the planet…It’s probably for the best, for if that had indeed been the case for a billion or so years of Earth’s history, our advanced form of life likely wouldn’t be here yet, or perhaps ever.”

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