6 Out Of the swamp Somewhere in all the gases minerals and water that collected on Earth in earliest times were the tiny elements that could create a single cell of a substance called protein We are made of protein cells as are all living things Bubbling planet The earliest forms of life didn t look like any kind of creature we know today These were bacteria tiny organisms that lived in hot bubbling mud But as the planet cooled some organisms began to use sunlight carbon dioxide gas and water to photosynthesize a process which created their own source of food And at the same time they gave off oxygen As the bacteria started to give off oxygen this allowed them to develop in new ways as algae fungus slime and as tiny single-celled creatures called amoebas A baby swims freely underwater Baby fish We are a water animal For about 8 months before we are born we are swimming around in fluid in our mother s womb We have had lots of practice at breathing underwater and today many very young babies continue to swim easily underwater under supervision of course
7 Wet tO dry Amoebas thrived and eventually evolved into a beetle-shaped creature called the trilobite From then on animal life started to develop in many forms as fish and then as animals that could breathe in or out of water Over time some of these animals evolved four legs that they used to haul themselves onto land Stromatolites have been living on Earth for 3 6 billion years The Oldest living things Scientists are continually finding older and older fossils proving that living things were developing on our planet billions of years ago The oldest found so far are stromatolites Amazingly these have survived as gray spongy plants that grow in the shallow waters of a remote part of Australia KEY WORDS protein bacteria algae amoeba trilobite stromatolite ice life elsewhere The universe is far too enormous there are trillions of planets to know whether we re the only one with water in liquid form What we do know is that we re the only planet in our solar system with surface water There s water on many planets and moons that orbit our Sun but only in the form of ice Is there water on the 250 or so other planets that we have discovered Who knows
8 and On tO the ice Age Of ice For most of its history Earth has been hot But today we are living in one of the many ice ages that started over 2 billion years ago This one started 40 million years ago and we are only just coming out of it Before then Earth was a greenhouse world with no major ice sheets After this time a very slow drop in carbon dioxide levels made Earth switch quickly from a hot-house world to an ice-house world which is when the Poles began icing over At the pOles At the north and south poles the planet s water becomes ice The poles are located at the far north and far south of the planet Both are farthest from the Sun depending on where the Earth is in its solar orbit This makes them cold so much of the water at the poles becomes ice Snow and ice can collect high in mountainous regions but the force of Earth s gravity pulls them down They form a flowing eriver of ice called a glacier that makes its way to lower ground and the sea Glaciers carve out U-shaped valleys as they move
BelOw freezing We are taught that the freezing point of water is 32 degrees Fahrenheit F However scientists have now found that water doesn t always freeze at this point In fact they can actually control the temperature at which it will freeze Ice crystals prefer something to form on h a particle of dust or a rough surface The scientific team found that dust-free water on a smooth clean surface will drop well below 32 F before it freezes 9 The Franz Joseph Glacier in New Zealand grinds its way downhill The big thaw Over recent years the average thickness of sea ice over the whole Arctic has fallen by 10 2 inches or 10 compared with the average thickness of the previous five winters The sea ice in the western Arctic lost around 19 inches of thickness and some channels became ice free for the first time in 30 years KEY WORDS ice age carbon dioxide gravity glacier valley Arctic Trapped in ice Today things are not nearly as bad as in the grip of an ice age but we are still thawing out from the last one A lot of Earth s water is still trapped as ice Most of this is at the South Pole where the ice can be up to 10,000 feet thick
