This is one of my favorite topics to think about! Great question! Ultimately, lithium was first made a few minutes after the Big Bang, or the creation of the universe, in a process call nucleosynthesis. However, lithium continues to be created today by stars because all stars also go through a form of nucleosynthesis.

Thus, the lithium on Earth today was formed in the Big Bang (about 13.7 billion years ago), the formation of our Sun (about 4.567 billion years ago), and from the stardust that our Sun formed from.

It is thought that our universe was created from the Big Bang about 13.7 billion years ago. It is difficult to explain how exactly the Big Bang might have happened, but you can imagine it as an incredibly super hot and dense point of sub-atomic size that almost instantaneously expanded to the size of a golf ball. This event, like an explosion, created matter in the form of neutrons, protons, electrons, anti-electrons, photons, and neutrinos. Hydrogen, the first and lightest element, is made up of a single proton nucleus, so the first matter formed by the Big Bang was hydrogen (also called protium). However, as the universe expanded and cooled, protons and neutrons collided to form deuterium (an isotope of hydrogen), helium, and lithium. It also formed tritium (the third hydrogen isotope) and beryllium which are unstable and radioactive, so both quickly decayed to helium and lithium, respectively. This process is call Big Bang nucleosynthesis, and is calculated to have occurred within 20 minutes of the Big Bang! These three elements - hydrogen, helium, and lithium - formed the first stars. All heavier elements were formed much later in evolving and exploding stars.

Nucleosynthesis is the process by which new atomic nuclei (the very dense center region of an atom, made up of protons and neutrons) are formed either by nuclear fusion (two nuclei joining to create a larger nucleus) or nuclear fission (one large nucleus dividing or splitting to form two smaller nuclei). Big Bang nucleosynthesis occurred within the first twenty minutes of the formation of the universe and created hydrogen, helium, and lithium. All the heavier atoms up to iron are formed by stellar nucleosynthesis, when nuclear fusion occurs in the core of stars. The longer a star lives, the more heavier elements that can form. Stellar nucleosynthesis still occurs today in the lifespan of every star, and will continue to occur in each new star that forms.

All the elements between magnesium (atomic number 12) and nickel (atomic number 28) are formed by supernova nucleosynthesis, within the core of exploding supernova. Elements heavier than nickel are formed through the capture of neutrons (r-process), the capture of protons (p-process), or directly by the explosion of supernova. There are a few other processes that also create different isotopes, but these are the primary ways to form the different elements.

To summarize, 13.7 billion years ago the Big Bang formed the first parts of matter. A few minutes later the element lithium was born. Billions of years go by with lithium being formed in new stars and destroyed in old stars. Then, 4.567 billion years ago our solar system formed, creating lithium in the birth of the Sun. Earth's lithium originates from all those billions of years of events. A final concept to think about is that when the solar nebula collapsed and created our sun, space debris (asteroids and meteoroids) was formed. Occasionally that debris hits Earth's surface and scientists are able to observe what Earth's original composition would have been made of. Pretty neat!

Lithium was made before there were rocks. The 3 lightest elements are Hydrogen, Helium, and Lithium. All 3 should have been made during the Big Bang, when the universe first began. Hydrogen and Helium were made, but Lithium seems to have been made later, but still before there were rocks and planets. This mystery is described here: big bang and elements

Well, geologically speaking, we would say that the answer would be the Big Bang. Light elements (like hydrogen, helium, and lithium) were made during the Big Bang.

With that in mind...if that's how light elements were made, where did all the other heavier elements come from...?

For some background, elements are defined by how many protons they have (atomic number). So if you wanted to make a new element, the easiest way to do it would be to simply smush other elements together. However, this process (which has the technical name of nuclear fusion) isn't so easy, and is only possible with great amounts of heat and pressure which only readily exists inside of stars. Sometimes elements that form this way are unstable though, and will also decay (by releasing neutrons and protons) to become more stable elements. Check out this website for a little more information.

Also, if you're interested, check out these wikipedia pages for a bit more context!

Lithium is not created geologically. It's not even made in stars; stars destroy lithium as they turn it into heavier elements. What lithium exists in the universe was created during the big bang, as the then third most-common element, after hydrogen and helium, but there was such a tiny amount of it and stars have consumed most of it.