The very first stars are called Population III (backwards, isn’t it), and then Population II and our Sun, a young star is Population I. The metal (all elements above helium in the periodic table, in astronomy speak) abundance is essentially zero in Pop III but as stars age the heavier ones form metals in late stages of thermonuclear fusion in their cores. In nova and supernova events these are recirculated into the intergalactic medium and end up in gas clouds that form new generations of stars.

So after much recycling, some 9 billion years later, there was a gas cloud that formed the Solar system, including the Sun, Earth, other planets, moons, asteroids etc. And by that time about 1% of the mass was in heavy elements, including carbon, oxygen, silicon, iron, that were all needed to form Earth as we know it. Most of our pure hydrogen and helium escaped since the Earth’s gravity couldn’t hold them. (The hydrogen we have is mostly locked up in water, etc.).

And all sorts of interesting chemistry was made possible.

The Big Bang did not create these heavy elements that make up most of the Earth’s mass, it took multiple generation of stars to do that.

⬛️Plants and animals both owe their origins to endosymbiosis, a process where one cell ingests another, but for some reason then fails to digest it. The evidence for this lies in the way their cells function. Both plant and animal rely on structures called mitochondria to release energy in their cells, using aerobic respiration to produce the energy-carrying molecule ATP. There is considerable evidence that mitochondria evolved from free-living aerobic bacteria: they are the size of bacterial cells; they divide independently of the cell by binary fission; they have their own genome in the form of a single circular DNA molecule; their ribosomes are more similar to those of bacteria than to the ribosomes found in the eukaryote cell’s cytoplasm; and like chloroplasts they are enclosed by a double membrane as would be expected if they derived from bacterial cells engulfed by another cell

⬛️Like the plants, animals evolved in the sea. And that is where they remained for at least 600 million years. This is because, in the absence of a protective ozone layer, the land was bathed in lethal levels of UV radiation. Once photosynthesis had raised atmospheric oxygen levels high enough, the ozone layer formed, meaning that it was then possible for living things to venture onto the land.

⬛️The oldest fossil evidence of multicellular animals, or metazoans, is burrows that appear to have been made by smooth, wormlike organisms. Such trace fossils have been found in rocks from China, Canada, and India, but they tell us little about the animals that made them apart from their basic shape.