Updated Answer - NO DAMAGE!
Crawford confirmed that the wording of Earthbind was "probably too subtle" and that the intent is for no damage.
The earthbind spell doesn't cause the target to fall. Probably too subtle: that's why the spell uses "descends" instead of "falls."
This makes sense with the use of DESCEND vs FALL.
Below is my original answer which covers some good discussion, so I'm leaving it there.
The plus side is that if you have the time, Earthbind can be used as an Action-Cost Featherfall.
PREVIOUS ANSWER, NOW INCORRECT
The language of Earthbind creates a problem in interpretation. The Spell states(from Elemental Evil 17):
The target must succeed on a Strength saving throw or its flying speed (if any) is reduced to 0 feet for the spell's duration. An airborne creature affected by this spell descends at 60 feet per round until it reaches the ground or the spell ends.
What's unclear is what is happening when the speed is reduced to 0 and what "descends at 60 feet per round" means in terms of reaching the ground.
My assessment below is based on a literal RAW reading of the spell against similar abilities and spells along with the general rules of 5e.
Flying Speed Reduced to 0
The PHB, 191 has the rules on Flying Speed:
Flying creatures enjoy many benefits of mobility, but they must also deal with the danger of falling. If a flying creature is knocked prone, has its speed reduced to 0, or is otherwise deprived of the ability to move, the creature falls, unless it has the ability to hover or it is being held aloft by magic, such as by the fly spell.
It is clear here that when a flying creature has it's speed reduced to 0 and has no means of hover/magical flight then they fall.
Unfortunately, the language of Earthbind doesn't allow for Hover/Fly to bypass falling. The spell is actively pulling a creature to the ground.
This leads to the question of the type of descent (controlled vs uncontrolled) and what happens when they reach the ground.
Hitting the Ground
This is the problematic part of the spell due to it's lack of clarity. It doesn't say that there is no damage upon 'impact', but it also doesn't say that it would deliver damage.
What we can do is look at some relevant mechanics
Monk's Slow Fall - PHB 78
Beginning at 4th level, you can use your reaction when you fall to reduce any falling damage you take by an amount equal to five times your monk level.
Feather Fall - PHB 239
If the creature lands before the spell ends, it takes no falling damage and can land on its feet.
Wind Walk - PHB 288
If a creature is in cloud form and flying when the effect ends, the creature descends 60 feet per round for 1 minute until it lands, which it does safely.
The implication of these three is that when a creature falls from a height, it takes damage unless the language specifically states to mitigate it.
Earthbind doesn't have any language to mitigate damage.
Is Descending considered Falling?
Given that the creature has a fly speed of 0, is actively being forced to the ground, and has no way to maintain or prevent hitting the ground (due to speed of 0), and the differences in mitigation language between other 'falling' type spells strongly suggest yes.
However, "Descent" could also be considered Controlled and therefore wouldn't be an impact, but instead be a landing.
The big arrow pointing to "Falling" is mostly because it doesn't state "landing safely" or "takes no falling damage".
Clearly, the big assumption made here is that being pulled to the ground is the same thing as falling. Given the language of the spell and it's harmful nature, it is not a wrong assumption to make. But because it doesn't clearly state that is the case, it does allow for the interpretation that the creature isn't Falling and would just be placed on the ground. If your DM rules as such, it is a reasonable call to make - but it is worth having a discussion about the reasoning as other spell/ability language seems to suggest otherwise.
We've also been given an unofficial 'window' into the design intent of Mike Mearls. Please note that, unlike Jeremy Crawford, his tweets are not considered Official by Wizards of the Coast.
Mike Mearls, via Twitter
yes, falling damage. hover creature falls, too (can't fly at speed 0)
The implication is that most creatures will take damage upon reaching the ground. Hovering or creatures who can magically Fly would normally resist "falling", but that active pull of Earthbind prevents them from doing so and drags them to the earth, kicking and screaming until impact.
However, allowing creatures who have Magical Flight or Hover abilities (not just a flight speed) to arrive safely would be reasonable as well.
Falling Damage is listed in the PHB 183.
At the end of a fall, a creatures takes 1d6 bludgeoning damage for every 10 feet it fell, to a maximum of 20d6.
Calculating how much damage may be confusing. When doing so, there are a couple of factors to keep in mind. You can look at the total distance the creature was pulled, or you could do just the final distance in the turn.
5e doesn't have a mechanic to calculate velocity, the damage is purely based on distance.
The Simplicity of 5e vs the Complexity of the Real World
It's important to note that 5e is not a simulationist RPG and that the ruleset is purposefully simplified. Trying to integrate and rationalize real-world physics to 5e rules simply doesn't work. It doesn't mean that you can't adjust your damage totals at your table, but the simplicity often means exactly what it says in the book. In this case, the creature has dropped X feet from point of spell to ground and for every 10' of descent they get 1d6 bludgeoning damage. Falling damage in 5e is calculated based on distance, not on speed.
The designers made things simple. But doing so means the rules often don't mesh with the real world. Adjusting at the table is fine, but then that's a houserule to add a complexity that doesn't exist in the base rules.
Feather Fall (1st level) vs Earthbind(2nd Level)
Another thing to consider is that if you do rule that there is no damage upon reaching the ground, then this becomes a Feather Fall Variant. It does all the same things, except it's an action not a reaction, requires a save, and it can drag someone down rather than simply soften their landing. If you've got the time (1 action) before you hit (if you're high enough), you can cast this on yourself/someone to act like a featherfall. I'm not sure that's the intent, but it's another way to use it IF you rule no damage.