Expanding Earth

Imagine you have a ball that is your world. It’s a pretty big ball, but not all that big compared to other ones you would find in space. Now, imagine that this ball is getting bigger and bigger over time. It’s not like someone is just adding to it, but it’s actually stretching and getting bigger all by itself. This is what we mean when we talk about an expanding Earth.

Here’s a little more on how this happens: Our Earth has a crust which acts like the shell of an egg, covering and protecting everything that’s underneath. At the bottom of the crust, there are things called tectonic plates that make up the “motor” of the Earth. They move and grind against each other, which is what causes earthquakes and volcanic eruptions. But over millions of years, these plates are also pushing against each other, kind of like how your hands press against each other when you’re trying to push something.　

When something pushes against something else, they get crumpled or compressed. This is why your clothes get wrinkled if you forget to fold them after doing laundry. In the same way, because the tectonic plates are pushing against each other, they squeeze the Earth’s crust from all sides, and this causes the Earth's crust to expand over time. You can think of the Earth's crust getting bigger like a balloon getting bigger as you keep blowing air into it.

Now, before you get too excited and start thinking that we are floating away from the Sun, don't worry - the expansion is happening really slowly, like a snail. Scientists believe that the Earth has been growing about an inch a year over the past several million years which is comparatively very slow. This is why it is difficult to notice any significant changes in the size of the Earth over a human lifespan.

So that is the ELI5 version of what happens when we talk about an expanding Earth. It's like an inflatable ball that's slowly growing bigger but the growth is so slow that we cannot even notice it!