There is no soilon Mars or Venus. How come? Those planets have plenty of rocks. Mars has windstorms that erode rocks into dust. Venus has an acid atmosphere that cooks rocks into new chemicals.

But there's still something missing. Without life, there is no soil. Living things haven't just made a home in the soil on our planet. Life actually made the soil as we know it. Here's the recipe:

First, select a large quantity of bedrock.You can start with a fresh lava flow, a solid granite dome, or some limestone. When weathered, or broken down, it will become theparent materialthat will make the next batch of soil.

Physical weathering:Next, break some of theparent materialinto pieces. Use a glacier to grind off big boulders and fine sediment. Wind or running water work great to make small mineral particles. Be patient. This can take several thousand years.

Chemical weathering:Now change some of theparent materialand the mineral particles into other kinds of minerals. Run water over limestone to dissolve the limestone and make the water more acidic. Expose fresh rock with iron in it to the air tooxidizethe rock. This can also take a while. But you can go on to the next step while this cooks.

Biological actions:Finally, start with some early colonizers like lichens. Then throw in a stock made of microscopicdecomposers. These include bacteria, fungi, andprotozoa. They all makehumusout of deadorganic matter. They also turn minerals from theparent materialinto nutrients that plants can use. Pretty soon you'll have enoughhumusfor plants to begin growing. Your soil will now start to have a distinct structure. Instead of being just dust or sand, it will clump together. Water will stay longer instead of draining away.

Sprinkle in plenty of tinyarthropodslike mites and springtails. They'll pass theorganic matterfrom the plants on to the smallerdecomposers.

Don't forget a dash of some larger animals like earthworms, moles, and gophers. They'll loosen the top layer and stir air in for you.

Simmer slowly in the sunshine for at least a few hundred years. Add rain regularly as needed. Now you've got living, breathing soil. Yummy!

Pictures: Saskatchewan Interactive/Dr. Jeff Bettany | Point Pelee National Park, Canada |
NASA | U.S. Geological Survey | John Allison | ArtToday (2)

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