Life Has Changed Earth

Oxygen Releasing Microorganisms

Earth looks like it does today due, in part, to the plants and animals that live here. The first major change life made to Earth was the Great Oxygenation Event. Blue Green Algae developed the ability to photosynthesize. This released massive amounts of oxygen into the atmosphere of Earth when previously there had been none. It caused a mass extinction of other microorganisms, led to a temporary freezing of Earth, and made it possible for all the life forms we see today to exist. This oxygen also reacted with the molecules on earth and formed layers of iron oxide in sedimentary rocks and allowed about 4,000 new mineral varieties to form.

Landscapes

Microorganisms in the water that runs underground produce sulfuric acid which helped to dissolve the limestone underground to create beautiful underground caves found all over the world. Without life there would be no white cliffs of Dover. Chalk is a sedimentary rock that is made from the calcium rich remains of microorganisms.  Soil comes from the remains of once living organisms that have decayed. It is held in place by the plants that grow in it.

Fixing of Ammonia

There are some microbes that can take the nitrogen in the atmosphere and change it to ammonia. In 1910 Haber devised a process to make ammonia from nitrogen so that it could be used as fertilizer for farming. As a result more food could be grown and the world population increased from 1.6 billion people in 1900 to 7 billion today. While the increase in land use for farming has allowed many more people to be fed, it has also led to soil erosion because less land is covered in forests. Overgrazing can also cause this.

Humans Have Changed Living Organisms

When humans transitioned from hunter gatherers to farmers, they changed the plants and animals they found in the wild to suit their needs. For example, wild boars were bred to be the pigs found on farms today and a wild grass plant called teosinte was bred to be corn. People domesticated animals and created food crops by selectively breeding the plants and animals.

This is a graph that depicts one generation of artificial selection. In this chart we have an example of a trait. In this case it is the purple color of a flower. This is an example of a trait that is controlled by many different genes in this plant’s DNA. The x-axis of this graph shows the flower color. The y-axis represents the frequency of each color of flower. You can see that the color of the flowers is normally distributed (it makes a bell curve). The first graph depicts the parent population. One of the lighter colored purple flowers is the most commonly found color for this flower. The flowers with the two darkest colors were chosen to be the only parents for the next generation. Because there are so many genes that determine this trait, the color of the flowers in the offspring are still normally distributed, however, you can see the mean of the offspring’s generation has shifted to a darker flower color. The change in the mean between these two generations is called the narrow sense heritability. After many generations of repeating this process you will get increasingly more plants with your desired trait.

Activity

I have drawn a hypothetical wild plant. I asked the kids to decide how they would change this plant to be more useful to humans. I gave them the picture below and had them draw a new version of it.

Here is what some of the kids came up with. As a group I had the kids give some examples of how they could change the plant to help each other with ideas.