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Fossil shells like this one contain details of dinosaur day lengths

Image: Wikimedia commons/Wilson44691

The dinosaurs lived many millions of years ago. Since then, many things have changed about our planet. The oceans and continents have shifted, ecosystems have changed and lots of species – including dinosaurs – have become extinct. Even the regular patterns of sunrise and sunset might have drifted. But without looking in a Cretaceous calendar, how can we learn about a dinosaur’s day?

The answer was found hiding in a fossilised shell from the late Cretaceous period, about 70 million years ago. Belgian scientists noted that the shell came in tiny layers, each thinner than a sheet of paper.

Like tree rings, the layers show how the creature grew over time. One layer represents a day of growth in these shells. These layers also changed with the seasons, allowing the scientists to see both years and days in the same shell.

When the team counted the layers in one year of growth, they didn’t find 365. Instead, this ancient shell had 372 daily layers for each year of growth!

As surprising as it might seem, other scientists had already predicted this outcome. Earth’s days are getting longer, so fewer fit into a year. Astronomers know this from studying records of eclipses from thousands of years ago. And physicists can measure the length of a day using super-accurate atomic clocks.

But don’t worry about your calendar getting out of order! A day now is only about 1.7 milliseconds longer than a century ago. And if things get too out of hand, scientists sometimes add an extra second to the year – known as a leap second – to keep everything lined up!

Tides of time

If Earth’s spin is slowing, where is all that energy going? It’s going straight to the Moon!

The Moon’s gravity causes tidal bulges to form in the ocean. Earth spins, which pushes on the tidal bulges. As a result, Earth spins slightly slower, which gives the Moon a little push.

Over time, these pushes are moving the Moon further and further from Earth. Scientists reckon the Moon is escaping at about 38 millimetres per year!

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