4 A wet beginning Where did the very first water come from and how did it collect on Earth Earth is about 4 6 billion years old and it’s almost certain that water did not start here but arrived from outer space COmet cOllisiOns Water is thought to have been first delivered here over 4 billion years ago during a period when comets small icy bodies from the Solar System and asteroids tiny planets sometimes just a few feet across were battering the inner parts of the solar system These hurtled toward Earth at a speed of about 74,500 miles per hour making heavy pockmarks on its surface as they crashed The comets were made of interplanetary dust carbon and minerals as well as a stew of chemicals and gases In the depths of space some of these materials including the gases hydrogen and oxygen became altered and formed water Comets rained down on the young planet Earth H20 When two parts of the gas hydrogen combine with one part of oxygen H20 water is formed Luckily our Earth lies just the right distance from the Sun for liquid water to exist So over millions of years as the Earth cooled clouds of water vapor condensed or became liquid and fell to the ground as rain slowly filling the rivers seas and oceans
5 KEY WORDS comets asteroids solar system carbon minerals chemicals gas hydrogen oxygen amino acid HOt wet and primeval On this early Earth the air was thick with poisonous gases Lightning flashed in the sky as dense clouds of dust particles crashed together sending out electric charges It was hot far warmer than our weather nowadays And it rained and rained and rained almost continuously Geologists can tell all this from examining the layers of rock deep in the Earth s crust or where mountains have tilted and exposed the rocks Bubbling mud and swamps covered the land in prehistoric times Water life Water is an essential ingredient of life and our planet has lots of it Without water there would be no plants and animals certainly no people Parts of the stew that formed in the Earth s oceans usually called the primordial soup were the molecules we know as amino acids Amino acids are the building blocks of living things Scientists believe they came together in tidal pools to create larger organisms that eventually became the first plants and animals
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
