Natural Selection Image Map

Poor Farming Practices

What do you suppose will happen if a farmer plants his crops on a hillside? Rains might wash away the soil, right? Elsewhere, we showed you a picture of the Mississippi River and all the dirt that it contained. Where do you suppose that dirt came from originally?

When rivers flood, the dirt they carry settles out and helps to enrich the fields.  Much of that good soil is carried in streams and rivers and does not settle out until reaching the ocean.

This canyon used to be good for farming.

Mayan lands in Central America
where farmers burn their fields after harvest

What do you suppose would happen if you grew crops year after year and burned off the field instead of plowing it under? What happens to dead plant matter? Do you know that it helps the soil hold moisture? Plowing crops and keeping the dead plant matter decreases the soil erosion problem and also decreases the need for as much water.

Extent of the smoke from burning Mayan fields. Notice that it curls up along the U.S. Gulf coast. Source: NASA space shuttle photo.

Running Out of Oil?

How do we know how much oil there is in the world?  We do not know for certain. We can, however, make estimates. These estimates are based on:

  • The amount of oil coming out of wells and the rate at which the production declines over time
  • The size of new potential fields (as in Alaska) where wells have not yet been drilled.

You could estimate oil fields by making small drill holes to sample it. However, boreholes yield very narrow samples and may drill right past substantial deposits of oil. Size of a potential oil field is best determined by blasting sound waves into the soil and recording the echo.  Oil beneath the surface will reflect sound waves differently from echoes from rock.  Complex computer analysis of the echo data in three dimensions provides an estimate of the three-dimensional size of pools of oil beneath the surface. This technique is known as three-dimensional seismography.

We know we are running out of oil, but estimates of the time left vary enormously. Regardless of how much time we have left, we need to find new sources of energy. We need to do that now, even if we have enough oil, so that we can stop polluting our air and water with car exhaust and gasoline refinery wastes.

As for preventing oil spills in our lakes and oceans, we know how to do that just from observing how oil spills in the past have occurred. We just need to:

  • Replace old, leaky pipelines
  • Avoid human errors in handling of oil cargo 
  • Prevent accidents of tankers and barges
  • Prevent leaks and spills from off-shore drilling rigs


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