In nature, everything is connected to everything else. Our world is a unique place. We are a tiny speck in a universe that has evolved over billions of years from the ‘big bang’.  The story starts with chemistry, from hydrogen and helium come stars and galaxies (about 13.8 billion years ago) and from the nuclear reactions in the early stars come the chemical elements that are the building blocks of everything in our universe.  The hotter the star, the ‘heavier’ the elements it can generate.

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Our solar system probably formed from a rotating mass of rock and gas, collapsing under its own weight about 4.5 billion years ago. By this time there were many more chemical elements to build our solar system. Our sun is only hot enough to generate ‘lighter’ elements like carbon, oxygen and a little nitrogen, but the cosmic dust contains both light and heavier elements from other stars long gone. We also know that space dust includes molecules as well as original elements, including carbon based (or organic) molecules like formaldehyde (H2CO).  

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Earth took around 50 million years to form, first molten then with a solid surface. A collision with an object the size of Mars probably caused the loss of the material that formed the moon, and thinned the solid surface of the Earth. There was no atmosphere and no oceans at this time, but the planet (and the moon) was being bombarded by comets hurtling from the outer reaches of the solar system towards the sun. Evidence of the craters on the moon have been lost on Earth because of the movement of the thin crust over the still molten core. It is likely that these icy snowballs of cosmic dust ploughed into the surface, generating heat, releasing their contents including water. About 400m years ago the intense bombardment ceased (although there are still a few comets and one wiped out the dinosaurs). The radioactive core constantly brought new material to the Earth’s surface, including water and gases, contributing to the formation of the atmosphere and the oceans. As well as the dramatic comet impacts there was a gentler, stream of cosmic dust which brought amino acids, the building blocks of proteins and molecules (purines and pyrimidines) that are the sub-units of DNA, the life molecule.  

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As the Earth turned, it was warmed by the sun and gravity stopped the emerging oceans and atmosphere escaping. By 3.8 billion years ago there is fossil evidence of life on Earth, which we presume evolved from life molecules in the star dust driven by energy from the core.  There was very little oxygen in the early atmosphere and for millennia heat loving, oxygen intolerant bacteria ruled. Eventually, as oxygen accumulated in the atmosphere, cyanobacteria evolved using sunlight to generate energy with photosynthesising chlorophyll molecules.  By 3 billion years ago we have fossil stromatolites.  Primitive organisms evolved by co-operation or absorption - a process of symbiosis that generated photosynthesis, oxygen, enzymes, membranes, sexual differentiation and more. 

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This is the beginning of the story of the web of life on Earth. Chemistry, geology and oceans interacting with each other driving the slow spread of oxygen giving life which, equally slowly, moulds the surface of the evolving Earth.

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We really are stardust and we really do depend on this web of life for our survival.

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Billion =thousand million