Roots failure to convert is a problem that has been systematic throughout his career. He has turned just 26 per cent of his scores above 50s into hundreds.
"The day will come when he does start converting them as well as Steve Smith does or the other greats have done," England's Dawid Malan said.
"I think no matter who you are you want to be scoring hundreds.
"I think the number of 50s Joe scores I think in his own mind he would probably be disappointed he doesn't convert more.
"When that day does happen it will be scary to see how good he can be and how high his average can jump to."
The England captain's dismissal opened the door for wicketkeeper Jonny Bairstow to be caught behind for five the following over off Josh Hazlewood, off what was ultimately the last ball of the day.
Root had earlier combined for a 133-run fourth-wicket partnership with Malan, who went to stumps at 55 not out.
Malan spent 42 minutes stuck on 16 after tea, but provided the perfect rear-guard for Root even as the Aussies coughed up two chances - in the form of a Steve Smith drop and missed run out - to dismiss him.
But the No.5 must now contend with England's long tail, with the struggling Moeen Ali due in on Friday morning.
"I think it sums up where we've been this tour," Malan said.
"We've been on top for so long in games and we make one or two mistakes and we let the Aussies back.
"To be five-down now after hard work we've put in today is obviously not ideal."
- AAP