On naming conventions
There are three known inhabited worlds. Oddly, they all have the same name of ‘Earth’ but in the respective dominant languages. For convenience sake the world on which one is currently residing is called earth, and the other two worlds are referred to by their inhabitance. So if a person was on the elf world they would call it earth (in whatever language) and, refer to the other two worlds as the human world, and the dwarf world. This is just for common speech however. For anything official every world has to be referred to by species. While certain groups do object to these naming conventions, they are largely ignored since this is the simplest method that the majority of people can agree on.
On The Elf World
The elven home world has the lowest mass and therefore lowest gravity. This is very clear in the number of flying animals and the shear mass of things. Since things can become much larger due to not collapsing under their own weight like they would on the Dwarven and human worlds. The elves did initially build tree houses, but with the advent of modern engineering have since graduated to buildings. Now they have massive forests of skyscrapers, social status can be determined by how high up in the buildings one resides. Due to the low gravity, it is unhealthy for humans or dwarves to reside on the elf world permanently.
Of the three races elves have the highest average height of 195cm. They also have the lowest bone density, making them the most fragile of the three races. After a transition period, it is possible for an elf to live on the human world long term with no health risks. However, it is reportedly very uncomfortable and thus rather rare. Due to the nature of their cities elves hold wind users in high regard and are very careful with Pyros.
On The Dwarf World
The Dwarven World while it shares a similar level of gravity with the human world is much less hospitable. It has a much thinner atmosphere, making it difficult for humans or elves to breath on the surface, since it is the equivalent of being at very high altitude. Also, due to the thin atmosphere there are higher levels of ambient radiation. This made it advantageous to live as close to the ground as possible, or even under it. The better Dwarven engineering got, the deeper their cities could be dug. It is extremely unhealthy for any race to spend much time on the surface, and generally unhealthy for humans or elves to spend much time in the Dwarven cities.
Dwarves are, on average the shortest of the three races, but only about a foot shorter than humans. While it is still technically possible for dwarves to breed with elves and humans, their offspring would not be viable. They are on average, eight times better at fixing genetic corruption, making their instances of cancer significantly lower than that of humans and elves. This ability also gives them a life span about 50 years longer than that of the average human or elves. They find living on the human world extremely comfortable, so there is now a significant Dwarven population on the human world. Dwarves are notable for not having inborn abilities, but their priests have a far greater range of power than those of the human and elven worlds.
On The Human World
The human world has its claim to fame by being less extreme than both the Dwarven world and the elf world. Since both elves and dwarves can stay for extended periods of time without health concerns it is where the majority of diplomacy between the worlds happen. For this reason it is also where the headquarters of the religious council is. This makes the human world extremely important in the political fields, and therefore where the biggest number of holy wars has taken place. The human world also has the largest amount of biodiversity, since it is larger than the elf world and more hospitable than the Dwarven world.
Humans have a similar claim to fame as their world. They are less extreme than the other two mortal races. They are not a fragile as the elves, and don’t have the genetic healing capabilities of the dwarves. They fare better on the elf world than the dwarves, mostly because they are on average better with heights. They also do better on the Dwarven world than the elves, because of the low ceilings. Height wise they are on average in between the dwarves and the elves. They are capable of having viable offspring with elves, however, human-elf hybrids suffer from a number of genetic issues.
On the portals
The portals have connected the human and elf worlds almost as long a human history. While astronomers have determined where the two planets are in relation to each other they are in different galaxies. This makes travel between the two highly unlikely by any means other than the portals. Which god is responsible for the opening of the portals is unknown, and believed to be one of the ‘fallen gods’ also called ‘false gods’. The Dwarven world, however only became connected about 250 years ago. The portals were opened by the Dwarven god. Their opening lead to almost immediate if short hostilities. The lack of open war can be attributed to the religious council and the Dwarven great priests.