Evidence of life in Earth's oldest rocks

Did life on this planet begin only after a relatively long planetary evolution, until suitable environments emerged that allowed life to gain a toehold, or was the cradle of life ready and rocking when Earth itself was but an infant? An answer may come from a paper online in Nature by Nutman et al. that analysed 3.7-billion-year-old rocks in the Isua Greenstone Belt in Greenland. 

https://doi.org/10.1038/nature19429

http://www.nature.com/nature/journal/v537/n7621/full/nature19355.html