Short answers, pulled from the story.
Largely because life is a process rather than a substance, something matter does rather than something it is. There is also no knowledge of what living things outside Earth might be like. At least 123 separate definitions have been compiled, with no consensus, which is why most working biologists rely on description instead, listing traits such as homeostasis, metabolism, growth, response to stimuli, and reproduction.
It is controversial. Viruses have genes, evolve by natural selection, and replicate by self-assembly, which is why they are called "organisms at the edge of life." But they do not metabolise and cannot make new products without a host cell, and they lack cell membranes and the ability to grow or respond to their environment. They are most often treated as gene-coding replicators rather than true life.
Earth itself is about 4.54 billion years old. Life has existed for at least 3.5 billion years, with the oldest physical traces dating back 3.7 billion years. Molecular clock estimates place the origin around 4 billion years ago, and putative microfossils announced in 2017 from Quebec may be as old as 4.28 billion years, suggesting life emerged almost as soon as oceans formed.
Vitalism held that there was a non-material life-principle and that organic material could only come from living things. It began with Georg Ernst Stahl in the 17th century. The idea was undercut in 1828 when Friedrich Wohler made urea from inorganic materials, and again when Hermann von Helmholtz showed no energy is lost in muscle movement. Today it survives only in pseudoscience such as homoeopathy.
Six elemental macronutrients: carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. Carbon is the most abundant in organisms because it forms multiple stable covalent bonds. Five of those six build DNA, with sulfur the exception, appearing instead in the amino acids cysteine and methionine.