1. A vast ocean of air
The skies above us are teeming with scientific mysteries which we're only just beginning to understand.
We may think that we inhabit the surface of our planet but in reality we live at the bottom of a vast ocean of air that's dynamic, fragile and home to some of nature's most powerful forces. But how can life survive in such a hostile environment?
To answer this a team of international experts spent a month studying the skies and carrying out groundbreaking experiments from a giant floating airship while flying across America. This unique science platform was called Cloud Lab.
2. Exploring the troposphere
The troposphere is a turbulent layer of air that begins at the Earth's surface and ranges from 23,000-65,000 feet above sea level, depending on the latitude, season and the time of day. Its name originates from the Greek word tropos, meaning change.
To collect samples at extreme altitude, extreme measures are required. Former paratrooper Andy Torbet jumped from 26,000ft with an oxygen mask and a collection dish to gather samples from the upper layer of the troposphere or free troposphere.
It's now known that bacteria actually exists in clouds and scientists believe that it plays a significant part in the creation of rain but little is known about life higher up. Microbiologist Dr Chris Van Tulleken has discovered that living bacteria can exist well above 10,000ft in a hostile environment with low pressure, increased UV radiation, freezing temperatures, high winds and no oxygen or water.
3. Living in the death zone
The human body has the ability to adapt to altitude, something often utilised by athletes who use it to improve performance but above 26,000 feet no human body can acclimatise.
Human beings must flood their lungs with pure oxygen to work at extreme altitude, to avoid dissolved gases such as nitrogen forming bubbles in the blood leading to the bends. How microscopic life survives at such heights has been a mystery. One answer could lie in the form of tardigrades or water bears that can completely dry out and live in a state of almost suspended animation.
Exploiting the boundary layer
While much is known about insects living close to Earth's surface, research suggests that other species exist on a vast scale higher up into the boundary layer. In a 1km square patch of countryside surveyed over the course of a summer month, as many as three billion insects pass overhead.
Insects at altitude
In the daytime smaller insects such as the leaf beetle are swept up into the atmosphere by turbulent air and carried on the winds. As the sun goes down, fast moving streams of air are created which larger insects use to assist their migration, selecting the most favourable altitudes and air streams to travel in.
Noctuid moths such as the fall armyworm moth actively seek out these night-time air streams to carry them north and south across America following their migratory routes.
You don't need wings to fly. Some young species of spider travel long distances by casting strands of silk into fast moving air columns. These act like parachutes and sometimes take them into the upper atmosphere, depositing them on remote islands and distant mountains.
The Himalayan jumping spider lives as high as 22,000ft above sea level. Its only source of food at these extreme heights is stray insects blown up by the wind.
4. Scaling the heights
6. How high can you go?
Many species have adapted their physiology over millions of years in order to live higher up, but which do you think can survive at the highest altitude?