Have they still not found a sign of how the earth came to be?

Answer

Yes, we understand quite well how planets formed around stars.

It starts with the formation of the star itself. This is done by the contraction of a large cloud. During this contraction, not everything falls on the star: after all, there is matter that revolves around the star much too fast to fall on it. That matter eventually ends up in a large disk of gas and dust that revolves around the star.

In that disc, dust particles gradually start to stick together. This continues until quite large stones are formed. It’s a bit like what happens when you forget to vacuum in your bedroom: over time, small dust particles clump together into larger tufts of dust. In a disk around stars there is no one vacuuming and there is a lot of time and a lot of dust. Over time, blocks have developed that are so large that they attract each other. In the long run, a few large blocks will remain, and those are planets. It takes about a hundred million years before a planet like Earth is finally formed.

This general picture explains a number of properties of the planets of our solar system. It also corresponds with what we observe in other stars. We see disks around young stars, and there are also clear indications that increasingly larger dust particles are being formed in these disks. We do indeed see planets in older stars.

But all this does not mean that other stars have a planetary system like ours. Indeed, we see that planetary systems differ quite a bit from star to star. And also that the disks in young stars are not all the same. There is a lot of diversity in the sky!