La fixité du milieu interieur est la condition de la vie libre
[To contain the inside is to make free life possible.]
—CLAUDE BERNARD
T HERE MIGHT HAVE BEEN A MOMENT when the Earth was perfect and unblemished. This moment would have occurred maybe four and a half billion years ago, when a thin crust congealed on the surface, creating a vast membrane that separated inside (the hot core) from outside (outer space). The differential thus inaugurated immediately caused eruptions, the hot interior punching volcanic holes through the membrane to vent its agitated nitrogen, carbon dioxide, and water vapor on the surface. The roiling interior fluids pushed up humps and ridges, cones and mounds, while meteor impacts from the outside pressed out concentric mountain ranges with diameters in the hundreds of miles. The Earth must have looked like a dead body in the first throes of decomposition.
For perhaps half a billion years, the place was too hot for life. Water remained as vapor in an atmosphere rich in carbon dioxide, formalde-hyde, neon, and cyanide. Then, as the Earth began to cool, it rained for perhaps twelve thousand years without stopping, helping to create the first seas.
The surface of the Earth was black and white then, rather like the aseptic photos of the surface of the moon. The browns, the yellows, the reds, and the oranges that we associate with soil and rocks did not exist, because all of them are the signs of oxidized iron. In that early time, the iron was all dissolved in the water—it dissolved as easily as salt does today.
The falling rain scoured the fresh curves of the land, finding the weak spots and the fissures. Sheets of flow found the lines of weakness, concentrating into torrents and cataracts that swept fragments of the mineral elements into the new seas.
The sea was the proto-soil, where Earth, air, water, and the solar fire met for the first time. It was an inverse soil, you might say, with the liquid element providing the matrix for the mineral salts and for dissolved gases, a role that the mineral elements would later come to play. But from a certain point of view, all Earth’s later history is a consequence of that first mixing. In that sense, life is the story of bodies that learned to contain the sea.
One morning in the Archean Era, an assembly of chemical compounds, possibly a clay, obeying some divine suggestion, threw an envelope around itself and began to live. It now had an inside and an outside. The envelope regulated the flow of salts from one to the other, and back again, making the selective work of digestion possible.
In the three billion years since, organisms have merely perfected this design. Though those organisms were microscopic creatures that probably ate iron sulfides, while we are masterpieces of bilateral symmetry, capable of eating everything from steaks to nasturtium flowers, we and the plants and the microbes are all containers for a fluid that is very like the sea. Ours is red, because we use an iron compound called “haem” to multiply our ability to extract oxygen from the air. A plant’s is green, because it uses a magnesium compound instead of iron, to extract carbon dioxide. A sea squirt’s is colorless, and will run out of its body if you expose it for too long to the air. But all of them share a need for a very narrow spectrum of salt concentrations, derived from the first weathering of rocks in the Archean Era.
The bodies of plants and animals concentrate the salts of the Earth, selecting those ions which are of use to metabolism. Silicon and aluminum, though they make up a large fraction of the soil, are present only in trace quantities in humans and plants. Calcium, magnesium, potassium, phosphorus, and sulphur, by contrast, exist in increasing concentrations from soil to plant to man. The ratio for calcium is 1:8:40, for phosphorus 1:140:200.
Eon by eon, the creatures of the Earth have moved toward what biochemists call “osmotic independence,” that is, the ability to carry these salty fluids freely through the open air. They can walk around without drying out. The right sort of impermeable protective covering is needed—chitinous like an insect’s plates, or, better, keratinous, like fur—and the right sort of pumps, particularly excretory pumps and circulatory pumps, as means of getting salts in and out and moving them about.
The floating and the bottom-dwelling invertebrates of the seas are memorials to the earliest strategies for achieving this freedom, but though they acquired a skin, they did not acquire the ability to move under their own power. In a sense, they were and have remained cells in the vast organism of the ocean, which moves them at will. Ocean currents are furrows along which its life glides.
Freedom of movement comes with freedom from the rhythms of the sea. Even in our bodies, the lymph and the lung fluids are controlled by tidal forces, but our pumps by their constant work give us a range of freedom of movement that was previously impossible. The heart’s tissue is created to beat, and continues to do so even after it is separated from the body.
Life did not crawl out of the sea onto the land; it oozed from the sea into the land, the organic acids of its excretions joining with the carbonic acid of the rainfall to create the first soft mantle of soil on the Earth. Maybe two billion years ago, the cyanobacteria began to use the sunlight to make sugars, excreting oxygen. They were green or brown, and their scum spread into lagoons, up rivers. The oxygen reacted with iron, and for the first time there were orange, yellow, and brown colors in the earth.
This was the world’s first bloom. Scientists often attach to these colonies of free-living organisms the unattractive moniker “algal mats.” Dense symbiotic colonies of cyanobacteria, fungi, and molds formed crusts that held dissolved minerals in place, preventing them from washing into the sea. They probably had all the various beauty of the orange, the red, the yellow-green, the filamentous, and the ramified lichens that cling to rock surfaces today. More precisely, they may have resembled the similar colonies called “cryptogamic crusts” that survive in arid climates today, keeping enough moisture among them to support life in a hostile climate.
On the first soils in the first season of the Earth, individuation began. Separated now by a solid matrix instead of by the shifting waters of the sea, organisms found it possible to wave without moving away. Things could stay in one place. Burning high-powered oxygen, they would soon be able to wave one way while moving in a completely different direction.
Strangely enough, when you look for a creature to match the range of motion of the human hand, you find yourself back with the wiggling orange filaments of fungi and the gesture of acclamation of a spreading bacterial branch.