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KNOW IT ALL: Tuesday's Top 7 Stories at NBC News

From a state of emergency in St. Louis to a state of emergency in Colorado, see the stories we're following today.

Good morning. Here are some of the stories we’re following today:

1. Rifle-Toting ‘Oath Keepers’ Roam Ferguson’s Streets

Heavily-armed members of a group called the Oath Keepers showed up at Ferguson protests overnight, adding unease to an already volatile environment. Ferguson is under a state of emergency following demonstrations related to the anniversary of Michael Brown's death, and officials said the Oath Keepers — all former military, police and first responders — aren't helping anything. Read more in NEWS.

2. Hillary Clinton Blasts Donald Trump: ‘It's All Entertainment’

Clinton condemned Donald Trump's recent controversial statements about Fox News host Megyn Kelly and said she thinks the real estate mogul is "having the time of his life, being up on that stage, saying whatever he wants to say." Clinton dismissed Trump's bid for the Republican presidential nomination as "all entertainment." Read more in POLITICS

3. Colorado Declares State of Emergency Over Toxic Spill

Gov. John Hickenlooper declared a state of emergency after the Environmental Protection Agency said Sunday that 3 million gallons of wastewater had spilled into the Animas River. Clean-up efforts have helped turn the river from a bright orange to a greenish hue, and preliminary tests indicate little danger to fish or other wildlife five days after the spill. Read more in NEWS.

4. Huge Study Says Our Universe Is 'Slowly Dying'

A survey of over 200,000 galaxies has confirmed that our universe is slowly dying. The energy being produced by stars and other objects is about half what it was two billion years ago. But not to worry, it's still got a few billion years to go — at least. Read more in SCIENCE.

5. Google to Become Subsidiary of New Holding Company

Google on Monday announced a new corporate operating structure, creating a new company, Alphabet, which will count the Internet giant as a subsidiary. Alphabet will house the main Google businesses, such as search and YouTube, along with businesses managed separately, such as Nest and the investing arm Google Ventures. Read more in TECH.

6. Japan Restarts Nuclear Reactor Under Strict Rules

Japan restarted a nuclear reactor Tuesday for the first time since new rules were introduced in the wake of the 2011 Fukushima meltdown. The reactor was one of 43 taken offline and forced to pass stringent guidelines in the wake of the meltdown, which was caused by a devastating earthquake and tsunami. Read more in NEWS.

7. Child’s Body Found in Search for Missing 5-Year-Old

Police believe they have found the body of Jerold Joseph Williams, who went missing after wandering away from his mother at an Arizona campsite on August 6. Investigators have not yet identified the child's body, and a cause of death was not immediately disclosed. Read more in NEWS.

Nightly Spotlight: Hackers Show Off Skills

Hackers from around the globe are assembling in Las Vegas for the DEF CON Hacking Convention to share new tricks, trade industry secrets, and find work.