Our planet Earth is comparatively small, with an equatorial circumference of only 24,902 miles. Its surface area may seem immense at 196,950,000 sq. miles, but of this, 71% is covered by sea. The actual land surface covers some 57,510,000 sq. miles - 29% of the total surface area.
Once again, this seems vast until we take into account the largely uninhabited regions such as the huge areas of the Arctic and Antarctic, the deserts and wetlands. These regions are not always totally uninhabited, but they can usually support only very small populations.
Our world cannot grow any larger, yet the human population keeps growing every year! As of July 2015, there were 7.2 billion people on the planet.
Whilst the birthrate is slowing a little in parts of the Northern Hemisphere, in many other parts of the world, including developing countries, populations continue to grow.
This population explosion is responsible for most world environmental problems today; so whether our primary concern is cleaner air, purer water, the elimination of pollution, conservation of wildlife and countryside, more food to eat or a higher standard of living generally, our chances of achieving any of these things diminish as the population increase surges on.
The Earth's resources are immense but limited. We have a tendency to look to the short-term, rather than seeing the bigger picture of the future.
This is why it is so important that young people learn about looking after the planet - so that future generations of adults act responsibly with regard to the environment and create a future that is sustainable, both for humans and all the other species with which we share our world.