8-year-old Colorado boy is over halfway to becoming youngest to climb towering El Capitan

Sam Adventure Baker climbing El Capitan -- Yosemite's iconic vertical rock formation --which sits more than 3,000 feet above the valley floor. (From Sam Adventure/Facebook via CNN)

The Colorado eight-year-old who set out this week to become the youngest person to climb El Capitan in California's Yosemite National Park is over halfway to reaching the summit, his father -- and climbing companion -- said.

Sam Adventure Baker and his father, Joe Baker, started their trek on Tuesday and the journey is expected to last four days. They plan to camp one night on the top of El Capitan and then hike down eight miles on the fifth day.

"We just crawled into our sacs on our port-a-ledge. Sam is out like a light," Joe Baker said in a Facebook post just after 1 a.m. PT Thursday. "Lots of fun still to go. We got another big day tomorrow to get to our next hanging camp. Sam showed so much courage today. I was blown away at his resilience and stamina into the night. We have already crossed the halfway point. Up we go."

Joe said the climbing experience has already been life changing for both him and his son.

El Capitan -- the park's iconic vertical rock formation -- sits more than 3,000 feet above the valley floor. That's 2.5 times as tall as the Empire State Building, according to the Yosemite National Park website. El Capitan is a Class 5 climb, according to Rei.com -- the highest and most difficult of classifications.

"He seems really happy to be up there and spirits are high," Sam's mother, Ann Baker, told CNN in an interview.

Ann said Sam grew up in a climbing family and she has always been "100% supportive of Sam's climbing adventures."

Ann and Joe fell in love rock climbing and Sam "was in a harness before he could walk," Joe told CNN.

After making it about a third of the way up El Capitan, Sam and his father "ate Mac and Cheese and watched the first half of the Lion King," before camping for the night, Joe said in a post overnight Wednesday.

"The stars are so bright that they cast shadows as they beautifully silhouette behind the Captian that ominously hangs over us. The coming pitches look so much steeper," Joe posted.

Sam had been training to take on El Capitan "every day for the last at least 18 months," his father said.

The father-son duo are climbing in a four-person team, which involves one person climbing ahead of the others and setting the ropes for the others to follow.