Seventy years ago this morning, the world fully entered the nuclear age with the detonation of the first atomic bomb in Alamogordo, New Mexico. The bomb was the product of the Manhattan Project, a top-secret research program tasked with developing a bomb more powerful than any that had come before. The test, called Trinity, happened at 5:30am local time and yielded an explosion equivalent to 20,000 tons of TNT (20kT).

The Manhattan Project, and the earlier UK effort, Tube Alloys, stemmed from pre-World War II physics research that revealed the huge amounts of energy that could be liberated from the fission of uranium atom nuclei, assuming a self-sustaining chain reaction could be started. The bomb used in the Trinity test, called Gadget, used high explosives to compress plutonium into a critical mass. It was the same design used in the bombing of Nagasaki on August 9, 1945; the bomb used on Hiroshima three days earlier was a cruder design.

Robert Oppenheimer, a physicist chosen to lead the bomb's development, greeted the appearance of a second sun over the desert of New Mexico with a quote from a Hindu scripture, the Bhagavad Gita: "Now I am become Death, the destroyer of worlds."

Trinity was the first human-made nuclear explosion on Earth, but far from the last. The USSR was hard at work on a bomb of its own, spurring an arms race between east and west that led to more than 2,000 nuclear bomb tests by 1998. The US and USSR were responsible for the overwhelming majority, although France, the UK, China, India, South Africa, Israel, and Pakistan all joined the nuclear club over time.

Growing worries about the harmful effects of radioactive fallout drove nuclear tests underground in 1963 with the passage of the Partial Nuclear Test Ban Treaty, and in 1996 most of the world signed onto the Comprehensive Test Ban Treaty (while the US signed the latter, it has never been ratified by the Senate).