It has been a week since Las Vegas police stormed Stephen Paddock’s hotel room at Mandalay Bay, finding him dead from a self-inflicted gunshot wound and surrounded by a personal arsenal of modified rifles. And in that time, we’ve learned quite a bit about him.

We know he was 64, had a house in Reno, a brother in Florida and a girlfriend he sent to the Philippines. We know he was a real estate investor and a gambler. We know he expressed no specific political ideology.

This is real, factual, vetted news and anyone can find it online. But in the hours after Paddock fired bullets into a crowded country music festival, hitting 547 people in the deadliest mass shooting in modern U.S. history, facts were hard to distinguish from falsehoods on Google, Facebook, YouTube and Twitter.

Hoaxes and conspiracy theories got dredged from the sewage-like depths of the internet. Wildly false rumors were dressed up as truth and put into widespread circulation. Items on the notoriously toxic 4chan network and Russian propaganda site Sputnik claimed the shooter was a liberal who hated President Donald Trump and loved MSNBC host Rachel Maddow, and was tied to Islamic State terrorists.

Once again, the Silicon Valley platforms that dominate public discourse and serve as a de facto source of information for billions of people delivered fake news that was damaging as well as confusing.

How long will this go on?

Two-thirds of American adults now get their news from social media. Facebook alone reaches a quarter of the human race.

It may not be uncommon for an explosive new technology to get out ahead of its creators, and surely the explosion of social media has rewarded its shareholders. But the rest of us can’t afford to wait much longer for some effective quality control, and some accountability.

After the dust-up over Russian bots and surreptitiously purchased political ads designed to influence last year’s presidential election, the executives of these California tech companies promised they would do better. Just last month they said they would add human fact checkers and expedite tweaks to algorithms that determine what news and which targeted advertisements rise to the surface to be seen by eager readers.

Behind the scenes, Facebook has agreed to partnerships with some news organizations — including McClatchy Co., parent of The Sacramento Bee — to increase the company’s credibility. And separately, Google and Apple worked with a few news outlets to steer people toward legitimate sources of information during Hurricane Irma.

However, to the extent Silicon Valley felt urgent responsibility for the broader risks being posed, it wasn’t apparent. Pressed on why so much fake news surfaced after the shooting in Las Vegas, social media companies put out tone-deaf, boilerplate statements citing technical difficulties.

“Unfortunately,” Google explained, “early this morning we were briefly surfacing an inaccurate 4chan website in our search results for a small number of queries. Within hours, the 4chan story was algorithmically replaced by relevant results. This should not have appeared for any queries, and we’ll continue to make algorithmic improvements to prevent this from happening in the future.”

On why Facebook’s “Trending Stories” section was suggesting an article from the Russian propaganda site Sputnik alongside articles from legitimate news agencies, a spokesperson told The New York Times: “Our Global Security Operations Center spotted these posts this morning and we have removed them. However, their removal was delayed, allowing them to be screen captured and circulated online.”

YouTube also changed its search algorithm to net more videos from mainstream news outlets — although it didn’t say which outlets counted as mainstream — after the site became clogged with conspiracy theories after the Las Vegas shooting.

But rampant disinformation isn’t just a question of fine-tuning some coding. It’s also a question of who will be accountable for lies, now that people can use technology to game the narratives that shape our civilization.

Social media has revolutionized our ability to communicate, but it has also made it easier to amplify and distort that communication. Who must take responsibility for that? Certainly not the machines.

Facebook, Twitter and Alphabet’s Google and YouTube must make dramatic changes, and soon. Beyond the responsibility that comes with such ability to influence, they could run a real and unpleasant risk of being regulated by Congress.

Already Virginia’s Sen. Mark Warner and Minnesota’s Sen. Amy Klobuchar have introduced a bill to require more transparency from social media companies that run political ads. Facebook, for example, would have to follow the same rules TV stations do. And on Nov. 1, executives from Twitter, Facebook and Alphabet’s Google have been invited to testify at a public hearing before the Senate Intelligence Committee.

There’s a good chance the fake news about the Las Vegas shooter will come up — and it should. It’s time that these companies enact policies to place some ethical boundaries around the information they present to the public. More must be done to prioritize responsibly vetted news stories. Computer algorithms absolutely should be supplemented by human employees.

Change won’t come easily. Billions of dollars in advertising revenue depend on maximizing the number of people spending time online.

But fake news isn’t a sustainable business. Only 37 percent of web-using adults believe the information they get from social media. That can’t be a promising metric.

There is no algorithmic shortcut for the responsibility humans have to society, to the truth and to each other. It’s time for Silicon Valley to show us it shares our values.

— The Sacramento Bee, Oct.8