By Rose Horowitch WASHINGTON (Reuters) -Ketanji Brown Jackson was sworn in on Thursday as a U.S. Supreme Court justice, making history as the first Black woman on the nation’s top judicial body while joining it at a time when its conservative majority has been flexing its muscles in major rulings. Jackson, 51, joins the liberal bloc of a court with a 6-3 conservative majority. Her swearing in as President Joe Biden’s replacement for retiring liberal Justice Stephen Breyer came six days after the court overturned the 1973 Roe v. Wade landmark that legalized abortion nationwide. Breyer, at 83 th…