CARL AZUZ, CNN STUDENT NEWS ANCHOR: Hi, I'm Carl Azuz. It is the worst oil spill in U.S. history, and it happened exactly one year ago. That story leads off this Wednesday edition of CNN Student News.

First Up: A Year Later

AZUZ: Blowout preventer, top kill, containment dome. A year ago, most of us had never heard of those terms. But they became part of our everyday lives as we watched the oil spill in the Gulf of Mexico unfold.

It started on April 20, 2010, with this explosion on the Deepwater Horizon oil rig. 11 of the 126 workers on the rig were killed in the explosion. The situation got worse when officials realized that oil was leaking directly out of the well and into the Gulf. Several early attempts to plug that leak completely failed.

That left this: a sheen that stretched across parts of the Gulf of Mexico. When a reporter dipped his glove into the water, as you see on your screen right there, you can see just how thick the oil was. Two weeks after the explosion on the rig, the oil reached shore, coating miles of beaches all along the U.S. Gulf Coast and having a devastating impact on local wildlife.

Eventually, engineers were able to seal the well and stop the leak, but not before more than 200 million gallons of oil got out. Check out what David Mattingly found when he journeyed back to the Gulf Coast one year after the spill.

(BEGIN VIDEO)

DAVID MATTINGLY, CNN NATIONAL CORRESPONDENT: Louisiana officials are watching their worst predictions come true. BP oil spill damage to some sensitive marshes may be permanent.

Are these marshes done for?

GARRET GRAVES, COASTAL PROTECTION AND RESTORATION: This area is likely going to be open water in a few years.

MATTINGLY: This is what this 40-acre section of marsh looked like when the oil hit last May. The syrupy crude I saw floating on the water then was just the beginning of the problem.

GRAVES: It's wiped out the birds that used to be here. It's wiped out the fish, the shellfish, everything in this area.

MATTINGLY: Returning 10 months later, the Louisiana governor's office gave me an exclusive and disturbing look inside this damaged ecosystem. I could still see oil everywhere, sticking to the plants.

It's like tar. So sticky. Look at that.

It's also saturated the fragile soil. You can find it a foot below the surface.

Right down here. Yes, it's down into the roots. Look at that. It's like a paste.

And Louisiana officials still look at all this oily black and see red. This confrontation was in December as parish President Billy Nungesser accused the Coast Guard of not doing enough to speed the clean up. After months of study, the Coast Guard now tells me digging out the oil in some areas will do more harm than good.

CAPTAIN JAMES HANZALIK, U.S. COAST GUARD: You can actually go in, you can trample oil into the marsh, where it would make it even worse than what it would have been if you would have just left it alone.

MATTINGLY: But letting nature take its course could mean watching more of these vanishing marshes wash away.

GRAVES: We're losing and trying to prevent the loss of...

MATTINGLY: Wait a minute. The wind just shifted. Do you know what I smell? It smells like freshly poured asphalt.

GRAVES: It does.

MATTINGLY: And there's fear that the oil we see in the marshes is only a fraction of what's here. There's oil underwater, too. This is how most people find submerged oil out here. It looks clean right now, but not for long. Hit it. Watch what happens as a couple of quick spins from our airboat churns up the sediment below and releases the hidden oil.

That's not mud we're looking at, is it?

Within seconds, a telltale sheen begins to form, a reminder that the losses suffered in this spill are far from over. So, as long as this oil is here, it's just going to keep killing anything that tries to live here.

GRAVES: It's going to keep killing, and you're going to have the birds who are going to come back and get re-oiled and they'll go fly somewhere else. And so, yes, the impacts are going to continue.

MATTINGLY: And that, officials say, could go on for decades.

(END VIDEO)

Columbine Remembered

AZUZ: This day in history also marks the anniversary of a tragic event that took place in Littleton, Colorado. On April 20, 1999, a shooting happened at Columbine High School. 13 people were killed; 23 others were wounded. The two shooters eventually killed themselves as well. The attack shocked the country. Former President Bill Clinton described it as "a day that changed us forever." This memorial to the victims of the shooting was unveiled at a park near Columbine High School in 2007.

Just the Facts

STAN CASE, CNN STUDENT NEWS: Just the Facts! The war in Afghanistan started in 2001 following the September 11th terrorist attacks on the U.S. A U.S.-led coalition removed Afghanistan's Taliban leaders from power. Taliban fighters eventually regrouped and are battling coalition forces to this day. There are currently around 100,000 U.S. troops serving in Afghanistan.

Threat of Insurgents

AZUZ: The U.S. is scheduled to start pulling some of those troops out of Afghanistan later this year. But Defense Secretary Robert Gates has said that the pace of the withdrawal will depend on the conditions in Afghanistan. Right now, coalition forces are facing a new threat in their fight against the Taliban. Barbara Starr explains.

(BEGIN VIDEO)

BARBARA STARR, CNN PENTAGON CORRESPONDENT: U.S. and Afghan forces in the remote mountains of eastern Afghanistan. Six U.S. troops lost their lives here trying to dislodge the Taliban and protect local citizens. But it's the threat of insurgents wearing Afghan uniforms and attacking once secure areas that is increasingly worrisome. Former Afghan war commander, retired Lieutenant General David Barno, says the Taliban are getting ready for a U.S. withdrawal.

LIEUTENANT GENERAL DAVID BARNO, U.S. ARMY (RETIRED): Their approach is not only to try and find ways to get inside the wire, as it were, to kill Americans, but also to suddenly undermine psychologically American confidence in their Afghan counterparts.

STARR: On Monday, a man wearing an Afghan army uniform entered the secure compound of the Defense Ministry and opened fire, killing two. Five U.S. soldiers were killed Saturday when a suicide bomber wearing an Afghan military uniform struck a military base. On Friday, the Kandahar police chief was killed by a suicide bomber wearing a military uniform. U.S. military officials say civilians still suffer most from the suicide attacks. In February and March of 2010, insurgents killed or injured 82 Afghan civilians. This year it was 353, a 330% jump. But Barno warns U.S. troops shouldn't feel too secure.

BARNO: We have felt in the past if we were inside of our bases and if we were working with our Afghan counterparts, that we were relatively secure. And I think that this whole strategy now puts that into question.

STARR: The U.S. military is now training Afghan units in basic counterintelligence so they can try to find infiltrators in army and police units before they attack Barbara Starr, CNN, the Pentagon.

(END VIDEO)

Shoutout

TOMEKA JONES, CNN STUDENT NEWS: Time for the Shoutout! The word "volunteer" can be traced back to what language? If you think you know it, shout it out! Is it: A) Greek, B) Farsi, C) German or D) Latin? You've got three seconds -- GO! We'll volunteer that the correct answer is Latin. That's your answer and that's your Shoutout!

Volunteer Month

AZUZ: April is Volunteer Month, a time when many Americans help others out without asking for a thing in return. Last year, more than 60 million Americans donated their time and efforts to a variety of causes. Many of you wrote on our blog that your schools are raising money for Japan. But you can find ways to make a difference right in your home town as well! CNN's "Impact Your World" program has a challenge for you. For 2011, they're looking for 11 hours of volunteer time, hoping to get a total of 111,000 hours by the end of the year.

Impact Your World

AZUZ: There are lots of ways to volunteer, and the "Impact Your World" site can help you find some of them. If you do volunteer, we'd love to hear about it. Take along a video camera; shoot an iReport for us. You can find a link to the "Impact Your World" page and one that explains how to submit an iReport at .

Before We Go

AZUZ: The finish line is almost in sight. So, on your mark... get set... ... sit down! It's the annual office chair race in a town in Germany. Organizers say all you need to compete are strong legs and a good chair. A helmet's probably a good idea, too, especially since you'll be navigating ramps and jumps on your way downhill. More than 60 people took part in the races. Sure, it's kinda popular now. But the first guy to try steering a work chair down a hill?

Goodbye

AZUZ: He was totally office rocker. If you get money for finishing first, we hope the winner donates it to chair-ity. That just kinda seems right for this kind of sit-uation. We hope you can stand more puns, because there are more coming tomorrow. See you then.

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