How does the atmosphere act as a "shield"?

The Earth is a rocky planet with a solid, active surface of mountains, valleys, canyons and plains. But what makes it special is water. It is an ocean planet: water covers about seventy per cent of its surface.

Its atmosphere is made mostly of nitrogen, with plenty of oxygen for living things to breathe. It is also a shield. Most of the small rocks from space that head towards the Earth burn up and break apart in the atmosphere before they can reach the ground.

The atmosphere is also just the right thickness to keep the planet warm enough for life. As far as we know, the Earth is the only planet in the solar system where life exists.

A day on Earth lasts a little under twenty-four hours, and a year lasts about 365 and a quarter days. Those extra quarter days add up to one whole day every four years, which is why we have a leap year.

You might think that we already know everything about our own planet. We do not. Satellites circling the Earth are still measuring its weather, oceans, soil and climate, and still discovering new things about the only home we have.