As the Marvel Cinematic Universe prepares to wrap up its Phase Three with Avengers: Endgame, coming to theaters this May, it's also celebrating its ten-year anniversary. The official Marvel Studios Twitter account has found a way to highlight how much has changed in the shared universe of its movies, and how much has stayed the same: side-by-side comparisons of some of its most popular characters during their early and current appearances.Using the hashtag #10YearChallenge with no other comment, Marvel Studios posted dual images of seven characters, including one picture representing their respective debuts in Phase One, and one showing the last time that the character was seen onscreen.RELATED: New MCU Posters Celebrate First 10 Years of Heroes & Villains

Some show obvious differences in hairstyle or signs of aging, while others stand out mostly for their similarities: Captain America (Chris Evans) wears an unchanging expression of disbelief, while Hawkeye (Jeremy Renner) always seems to be drenched in rain.

The "current" pictures for the heroes, taken together, tend towards a theme of bleakness -- most are taken from either the catastrophic ending of last year's Avengers: Infinity War, or the trailer for Endgame, which shows the characters contemplating their massive losses.

In the case of S.H.I.E.L.D. agents Nick Fury (Samuel L. Jackson) and Phil Coulson (Clark Gregg), the "early" pictures are the ones that had to be taken from trailers. Although both characters were introduced early in the Iron Man franchise, they're appearing again in Captain Marvel, which will be released this March but is set in the 90s, meaning that it's the most youthful version of them that audiences will have seen.

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Fans responding to the tweets were quick to take up the challenge. Many had jokes about their favorites turning to dust in Infinity War, or the hard-to-ignore change of an actor being replaced. One showed the evolution of the artificial intelligence system J.A.R.V.I.S. into the android Vision, voiced and then played by Paul Bettany. Some might take a moment to click, such as Drax the Destroyer (Dave Bautista) having no second picture -- of course, Drax believes he can turn invisible by standing still.

Judging from the enthusiasm and emotion running high in the thread, it appears that one thing hasn't changed in ten years: the fans are anticipating the next film with bated breath.

Avengers: Endgame will arrive on April 26. Directed by Joe and Anthony Russo, the film stars Robert Downey Jr., Josh Brolin, Mark Ruffalo, Tom Hiddleston, Chris Evans, Chris Hemsworth, Jeremy Renner, Chris Pratt, Elizabeth Olsen, Chadwick Boseman, Sebastian Stan, Benedict Cumberbatch, Paul Bettany, Samuel L. Jackson, Cobie Smulders, Benedict Wong, Zoe Saldana, Karen Gillan, Vin Diesel, Dave Bautista, Pom Klementieff, Scarlett Johansson, Tom Holland and Anthony Mackie.