On this date in history:

In 1500, Brazil was discovered by Pedro Alvarez Cabral.

In 1889, about 20,000 homesteaders massed along the border of the Oklahoma Territory, awaiting the signal to start the Oklahoma land rush.

In 1914, U.S. forces took control of the Mexican port city of Veracruz during the fighting of the Mexican Revolution.

In 1915, during World War I, German forces became the first to use poison gas on the Western Front.

In 1955, the drug industry urged the national polio conference to recommend the creation of an impartial committee to supervise the distribution of all Salk vaccine.

In 1970, Earth Day was first observed.

In 1972, Apollo 16 astronauts John Young and Charles Duke walked and rode on the surface of the moon for 7 hours, 23 minutes. Young, whose career with NASA began in 1962, would spend the next four decades as an astronaut, retiring in 2004 at the age of 74.

In 1985, Jose Sarney was sworn in as Brazil's first civilian president in 21 years.

In 1993, the Holocaust Memorial Museum was dedicated in Washington, D.C.

In 1994, Richard Nixon, the 37th U.S. president and the only one to resign from the office, died four days after having a stroke. He was 81.

In 1997, a 126-day standoff at the Japanese Embassy in Lima ended after Peruvian commandos stormed the building and freed 72 hostages held by the Tupac Amaru Revolutionary Movement. All 14 rebels were killed.

In 2004, former NFL star Pat Tillman, who turned down a lucrative contract with the Arizona Cardinals to join the U.S. Army Rangers, was killed in Afghanistan. The U.S. military said later he was a victim of friendly fire.

In 2005, Zacarias Moussaoui, the only man charged in the United States in connection with the September 11, 2001, terror attacks, pleaded guilty and was sentenced to life in prison.

In 2006, Iraq's Parliament ratified the selection of Nouri al-Maliki as prime minister, ending a four-month political deadlock.

In 2010, Russia banned Scientology literature for undermining the traditional spiritual values of the citizens of the Russian Federation.

In 2013, Boston Marathon bombing suspect Dzhokhar Tsarnaev was charged with conspiracy to use a weapon of mass destruction resulting in death. Eventually, Tsarnaev faced 17 federal charges in the April 15 attack that killed three people and injured more than 260. He was convicted in April 2015 on all charges.

In 2014, the U.S. Supreme Court upheld a Michigan law that bans preferential treatment on the basis of race, sex, color, ethnicity or national origin in admissions at public colleges and universities. It was a blow to affirmative action programs across the country.

In 2016, world leaders from 175 countries gathered in New York on Earth Day to sign the Paris Agreement, the first international accord that outlines steps to combat climate change and lower carbon levels by 2100.

Copyright 2017 by United Press International