Chapter 1 ARE WE ALONE The ancient Greeks believed that Earth was the center of the universe with the sun moon and planets all rotating around our planet In the fourth century BC the philosopher Aristotle 384 bc 322 bc wrote about the world as he saw it He said there could be no other worlds or aliens For centuries this is what people believed Other Worlds Aristotle’s writings may have very influential but in 1277 the teaching of some of his work was banned One of the newly banned ideas from Aristotle’s work was that God was unable to create many worlds All of a sudden people were allowed to consider worlds other than our own but most still thought that any God would probably not bother to create other worlds Later the philosophers Nicholas of Cusa 1401 1464 and Giordano Bruno 1548 1600 argued for the likelihood of other worlds More importantly they imagined them having life just like human beings or perhaps even more intelligent 4
If advanced alien life exists then it is outside the solar system If any aliens ever visit us they will be more technologically advanced than us They will have to have technology that allows them to travel between the stars This is ALH 84001 the meteorite from Mars In the center is a worm-like structure that scientists believed may have been a fossil Martian microbe Imagining Aliens Fiction has always been ahead of science when it comes to alien life The Syrian Greek writer Lucian ad 120 c 180 wrote True History in the second century In it people travel to the moon and are swept up into a war between the kings of the moon and the sun It also has aliens including dog faced men When H G Wells 1866 1946 wrote The War of the Worlds between 1895 and 1897 space exploration was 60 years away and people were able to imagine aliens from Mars invading us Now that probes have explored all the planets we know there are no intelligent aliens in our solar system But that has not stopped scientists from looking for more primitive life When the US National Aeronautics and Space Administration NASA announced possible fossil microbes in a meteorite from Mars in 1996 the news shocked the world Most scientists now discount this discovery and it became yet another shattered dream of finding alien life 5
WHAT IS LIFE If we are going to find life beyond Earth we will need to know how to recognize it Life is found everywhere on Earth from the coldest to the hottest places the highest peaks and the deepest parts of the ocean Life spans a massive range of forms including microbes fishes birds trees and mammals like us A Common Definition There is no definition of life in general but all life has things in common It has complex chemistry Life forms respond to changes in the environment around them like recoiling from something too hot or cold They make copies of themselves through reproduction They evolve or change over long periods of time as a result of natural selection They use up resources to eat and drink so that they can grow and they give out waste materials They are made up of tiny bits called cells Carbon can take more than one form Coal is almost pure carbon and the graphite we use in pencils is made from carbon Carbon can turn into diamond under extreme pressure and temperatures 6
All About Carbon One other thing all life has in common is the element carbon One of the 118 known elements carbon like the others has its own unique properties Different elements combine together in chemical reactions to make everything we know For example the gas oxygen likes to react with iron to make iron oxide or rust Carbon is able to make combinations of materials by reacting with other elements more than any other element All the chemistry needed for life involves carbon and most scientists agree that any alien life would also need this element Carbon is common on Earth and throughout the universe and so carbon based life is likely to be the only type there is The element most similar to carbon is silicon Some astronomers have argued that silicon based life which may be unrecognizable to us could exist However experiments in laboratories have shown that silicon cannot make the variety of chemicals needed for life If you could see the water content of your body you would see that we are made mostly of water Along with carbon water is an essential ingredient for life on Earth 7
