The only really hard part for me during the first 8 weeks was the abstinence from fruit and keeping away from the fresh bread! (taste.narin.com)
The absolute hardest part for me was juggling nap times and bedtimes. (breastfeedingneeds.com)
The Ediacaran gave way to the Cambrian explosion, 542 million years ago: the rapid emergence of new species with complex body plans, hard parts for defense, and sophisticated eyes. (sciencemag.org)