Earth — Our Home

What Is Earth?

Earth is the third planet from the Sun and the largest of the four rocky planets in our solar system. It is the only planet known to harbour life. From space, Earth looks like a brilliant blue marble — mostly covered in water, wrapped in white clouds, and streaked with brown and green landmasses.

Earth formed about 4.5 billion years ago from a cloud of gas and dust swirling around the young Sun. Over millions of years, gravity pulled this material together until it formed a solid sphere — our planet.

Why Does Earth Spin?

Earth rotates on its own axis once every 24 hours — this is what creates day and night. The side facing the Sun experiences day; the side facing away experiences night. But why does it spin at all?

When Earth formed from a swirling cloud of gas and dust, that cloud was already rotating. As gravity pulled the material into a ball, the rotation was preserved — much like a spinning ice skater pulling their arms in to spin faster. This rotation has continued ever since, although it is very slowly getting slightly longer each century due to tidal interactions with the Moon.

Earth's Layers

Earth is not solid all the way through. It has distinct layers, like an onion:

What Makes Earth Suitable for Life?

As far as we know, Earth is unique in the universe for supporting life. Several factors make this possible:

• The right distance from the Sun — Earth sits in what scientists call the "Goldilocks zone" or habitable zone: not too hot, not too cold, so that liquid water can exist on the surface.
• Liquid water — water is essential for all life as we know it. About 71% of Earth's surface is covered by oceans, lakes, and rivers.
• A protective atmosphere — Earth's atmosphere contains the oxygen we breathe, blocks harmful ultraviolet radiation, and acts like a blanket keeping temperatures stable.
• A magnetic field — generated by Earth's liquid iron core, this invisible shield deflects the solar wind — charged particles from the Sun that would otherwise strip away our atmosphere.
• Plate tectonics — the movement of Earth's crustal plates recycles carbon dioxide, helping regulate temperature over long timescales.

Earth's Atmosphere

The atmosphere is a thin layer of gases held around Earth by gravity. Without it, there would be no weather, no sound, and no life. It is made up mostly of:

• Nitrogen (78%) — the dominant gas, essential for plant growth
• Oxygen (21%) — what animals and humans breathe
• Argon (0.9%) — an inert gas with no significant biological role
• Carbon dioxide (0.04%) — small amount but critically important for plant photosynthesis and the greenhouse effect

The atmosphere also includes water vapour, which forms clouds and rain, and the ozone layer high above, which blocks the most dangerous ultraviolet rays from the Sun.