In History, Today on July 7

A retrial verdict acquits Joan of Arc of heresy, 25 years after her execution.

The Spanish conquistadors, led by Hernán Cortés, defeat a numerically superior Aztec army at the Battle of Otumba.

Sliced bread is sold for the first time by the Chillicothe Baking Company of Chillicothe, Missouri.

Construction of the Hoover Dam begins on the Colorado River.

The Marco Polo Bridge Incident occurs, marking the beginning of the Second Sino-Japanese War.

Mother Frances Xavier Cabrini becomes the first American to be canonized as a saint by the Roman Catholic Church.

Reports of a UFO crash in Roswell, New Mexico, spark widespread interest and conspiracy theories.

Elvis Presley makes his radio debut when WHBQ Memphis played his first recording for Sun Records, "That's All Right."

US President Ronald Reagan nominates Sandra Day O'Connor to become the first female member of the Supreme Court of the United States.

The first draft of the complete human genome is announced by scientists at the Human Genome Project.

A series of coordinated suicide bombings targeted the London public transport system during the morning rush hour, killing 52 civilians and injuring over 700. The attacks were carried out by four Islamist extremists and marked the deadliest terrorist incident in the United Kingdom since the 1988 Lockerbie bombing.

The Live Earth concerts, a series of music events, were held across seven continents to raise awareness about climate change. Organized by former U.S. Vice President Al Gore and the Alliance for Climate Protection, the concerts featured over 150 musical acts and reached an estimated global audience of 2 billion people.

The final mission of NASA's Space Shuttle program, STS-135, was launched. The shuttle Atlantis carried a crew of four to the International Space Station, marking the end of the 30-year Space Shuttle program that began with the launch of Columbia in 1981.

A train carrying crude oil derailed in Lac-Mégantic, Quebec, Canada, causing a massive explosion and fire that killed 47 people and destroyed much of the town's center.

A sniper attack occurred in Dallas, Texas, during a protest against police shootings of African Americans. Five police officers were killed, and nine others were injured. The gunman was later killed by a robot-delivered bomb.