life on other planets?

Question

why do people assume that there has to be oxygen and water to support life on other planets? humans may need these things but maybe "other" life forms don't.

Answer 1

It's true that life is capable of adapting to many different environments and circumstances and we mustn't be too narrow in our judgments of how life might exist on other planets.

However there are some basic principles of biology, chemistry and physics which must be adhered to if life is to exist (or at least exist in any form that we would recognise as life:-
+ life requires chemical reactions - without chemical reactions living things cannot grow, obtain energy, move or reproduce. Chemical reactions are too slow in solids and in gases the reactants would be too widely dispersed to ever come together in quantities that permit the kind of sustainable and controllable reactions that life appears to require. Therefore chemical reactions must take place in a liquid. Water may not be the only liquid that these reactions can occur in but it has a number of properties which make it ideally suited to the kind of reactions that could be expected to be required in the metabolism of a living thing. It is possible to speculate that other liquids might form the medium for metaobolic reactions but in almost all imaginable circumstances the liquid would also become part of the reaction, rather than just the solvent, causing immense difficulties in directing and controlling reactions to create sustainable life.

+ life requires that the living thing has a structure - a single atom or molecule is not defined as living. Structure requires the use of chemical elements that can bond together in a variety of ways and remain stable... such as chains and rings. Relatively few chemical elemennts can do this. In fact only carbon has the properties that enable it to do this really well and the only other candidate is the close relative of carbon, silicon. From time to time scientists have speculated on whether there could be silicon-based life-forms on other planets. While this would not be impossible, silicon life forms would have a number of unique and difficult problems to overcome, not least of which would be that the production of the wastes from most energy-releasing metabolic reactions involving silicon are likely to be solids such as silicon dioxide (also known as sand!).

+ life requires that the living thing obtains energy - it is a basic scientific principle that building something (placing it in an orderly manner, for example) costs more energy than destroying it or allowing it to become randomised. Living things can be defined as an orderly arrangement of molecules - no living thing could exist if its molecule were allowed to float around randomly over vast areas... they have to be contained and structured. This requires energy. There are only two primary sources of energy available as far as a living thing on another planet is concerned:- the star the planet orbits around and the geothermal energy from within the planet. Life forms have been identified here on earth which use either one or the other (obviously photosynthesis being the main one). The main problem is in creating molecules that store the energy and which then release it later in sufficient (and efficient) quantities. And here again the requirement is to build chemicals for energy storage (i.e, using carbon or silicon) and releasing energy which is a process that is most efficiently achieved by oxidation - and most efficiently of all by, in effect "burning" in oxygen.

These basic principles hold true throughout the universe as far as we are aware because it is inconceivable that different fundamental natural laws of physics and chemistry would operate in different places. Therefore although non-water and oxygen based life may be possible, the most efficient solutions to the problems faced by all life forms are likely to be based on carbon, oxygen and water.

Answer 2

The kind of chemical bonding needed to create nucleotides can only happen in the presence of water.

When oxygen is burned with sugar it produces energy. Organisms can live without oxygen, but not highly energetic species such as multi-cellular animals (fish, amphibians, mammals, birds, reptiles, insects, arachnids, etc.). Animals that move around have high energetic needs. Only with oxygen (and sugar) can we chemically produce such energy requirements. Nothing else works.

Answer 3

Water offers a medium in which chemical reactions occur. Without water we are lost. Ya na mean...

Answer 4

i belive there is a world out there similar to earth but they are thousands of years in front of us, we have screwed our world , but this parralelle world has learnt and looked after there world, and if world leaders decide to launch neuclear waste into space these other being from other planets will come down and lets just say visit earth.

this is what i think.

Answer 5

Define "life"

Answer 6

i believe there is endless life out there and even on mars but underneath the surface