After its fiery Hadean beginning, Earth seems to have spent up to a billion years covered completely in a world ocean. Volcanoes and small islands probably broke through the surface, but life’s first few 100 million years were probably underwater. Simple bacteria multiplied at the surface of this ocean and perhaps the bottom of the ocean as well. A variety of genes grew within this community as microbes grappled with different aspects of the environment, and they also began the balancing act that has stabilized the temperature. Life has made other substantial changes to the surface of the planet as well.
Continents grew as convection cells in the mantle circulated molten rock, allowing lighter silicates to ride to the top. Convection cells are self-generating forms of energy transfer that are to be seen from pots of soup heating on a stove, to the surface of the sun. It has been suggested that energy harnessed by early bacteria that selectively decomposed heavier minerals added to the separation action of this convection circulation, and significantly increased the size of the continents.
As photosynthesis prevailed as a source of energy in the bacterial world, the iron was precipitated as iron oxide from the ocean, and sank to the bottom, forming the redbeds which are the source of our iron today. As this same microbial action continued, oxygen built up in the atmosphere. The presence of this gas fundamentally changed the mineralogy of the new continents. The many minerals that are oxides result from this shift in the atmosphere. The ability of bacteria to harness different metabolic pathways has led them also to create ore deposits of uranium, manganese, aluminum and even gold.
All the fossil fuels that powered our industry until recently, came from the deposition of forms of life. The limestone and marble that we have used by themselves and for making concrete were deposited by single celled creatures in the oceans and the seas. Almost all the carbon at the surface of our planet has been locked up by life into these carbonates. Throughout this long process, life has cooled the surface, even as our sun has increased its intensity by 30%.
The action of life has directly digested rock all over the crust of the earth, both above the surface and within the rock itself. The large scale effects of this microbial activity are still largely unknown; however, what we have always thought of as the erosion of mountains over millions of years is more like their digestion.