Every Breath You Take

Imagine a beach ball tossed into a swimming pool. When it hits the surface, the ball’s momentum creates a shove that spins it around its axis. As the ball drifts across the pool and meets the resistant friction of water and air, the spin slows. Earth is something like the beach ball. It was formed billions of years ago from a spinning accretion disk of dust and rock. That spinning momentum continues today, the earth rotating about its center in twenty-four-hour cycles, but like that imaginary beach ball, the momentum is slowing, the pull of the moon’s gravity acting as a brake on the planet’s otherwise endless twirl.

Though imperceptible to us, the earth’s spin slows a tiny bit every second of every day. In fact, earth days become about two milliseconds longer with each passing century because of the slowing. Seventy million years ago, the planet spun faster than it does now, and tyrannosaurs had thirty fewer minutes in the day