Planet Earth

At 4.54 billion years old, our home world is a venerable object. But it was only with the arrival of the space age in the late 1950s that Earth was seen from a cosmic perspective.

This image of Earth, one of 77 composite photographs appearing in Otherworlds: Visions of our Solar System, gives an almost complete view of the planet taken a week before the northern hemisphere's summer solstice.

The swathes of blue dominating the image show that Earth's name is misleading: 70 per cent of its surface is in fact covered by water, predominantly in the form of vast oceans.

The blue marble

It is easy to take our oceans for granted, but Earth is one of only two places where stable bodies of surface liquid have been observed. (The other, Saturn's moon Titan, is home to lakes filled with a mixture of liquid ethane and methane – essentially lighter fluid.)

The oceans were probably where Earth's most remarkable feature emerged: life. Our planet is still the only place where we know life has arisen. The large green patches spanning Earth's continents stand testament to the abundant life they host.

Earth's magnetic field and ozone layer play a key role in protecting life, deflecting and absorbing potentially harmful solar radiation. And Earth's insulating atmosphere results in a generally temperate climate, providing excellent conditions for complex life.

Audio commentary extract

In this extract from the audio commentary for Otherworlds: Visions of our Solar System, planetary scientist and Mars expert Dr Joe Michalski introduces the exhibition, and discusses what we can learn from images of our planet.

• Download the audio commentary extract MP3 (2MB)