Original sentence: If this is the case, attempts to group everything then alive into one phylum are doomed to failure.Since representatives of almost all modern phyla were in existence by the Middle Cambrian, it is probable that the precursors of many phyla would be represented in the Ediacaran - a view which is supported by molecular clocks
Edited sentence: Since representatives of almost all modern phyla were in existence by the Middle Cambrian, it is probable that the precursors of many phyla would be represented in the Ediacaran and attempts to group everything into one phylum would then be doomed to failure