3. There is no such thing as silicon based lifeforms. Silicon's chemistry is quite limited. Carbon is also electronegative compared to hydrogen and silicon is electropositive compared to hydrogen. This has a drastic effect on silicon-hydrogen bonds. There aren't silicon equivalents for alkane, alkene, alkynes and zillions of other organic compounds.
I could envision silicon based life forms, primitive ones at least (maybe more primitive than a living cell), in a very hot environment, let's say, in an ocean of iron or so.
“Carbon and Silicon share many characteristics. Each has a so-called valence of four--meaning that individual atoms make four bonds with other elements in forming chemical compounds. Each element bonds to oxygen. Each forms long chains, called polymers, in which it alternates with oxygen.
But when carbon oxidizes--or unites with oxygen say, during burning--it becomes the gas carbon dioxide; silicon oxidizes to the solid silicon dioxide, called silica.”
https://www.scientificamerican.com/article/could-silicon-be-the-basi/Still, researchers have long speculated that alien life could have a completely different chemical basis than life on earth.
For example, instead of relying on water as the solvent in which biological molecules operate, perhaps aliens might depend on Ammonia and Methane. And instead of relying on Carbon to create the molecules of life, perhaps aliens could use Silicon!
“Scientists believe that Earth’s early atmosphere was probably mostly carbon dioxide with little or no oxygen. There were smaller proportions of water vapor, ammonia and methane.”
http://www.bbc.co.uk/schools/gcsebitesize/science/aqa/earth/earthsatmosphererev3.shtmlIt sounds like the perfect atmosphere for Silicon-base life forms, doesn’t it?
I think given the proper conditions on any planet, both carbon-based and silicon-based life might initially form.
“The surface temperature of Titan, Saturn’s largest moon, is a frigid -290 degrees Fahrenheit. The moon has little oxygen – any water is frozen – but liquid methane flows in strange rivers and lakes. The silicon-based compounds (called silanes) that could potentially build alien cells should be stable under those conditions.”
http://www.popsci.com/bacteria-have-bonded-carbon-and-silicon-for-first-time-what-can-they-teach-usSo, is it a possibility Silicon-base life forms and trees might’ve existed on earth in prehistoric times when earth atmosphere was suitable for such life to flourish? Based on the above; I think science answered a big YES!