Early Interactions Between the Fluid Spheres and the Young Earth

الأحد مايو 17, 2015 5:04 pm

Early Interactions Between the Fluid Spheres and the Young Earth

Earth’s youngest atmosphere was probably composed of the very light

elements hydrogen and helium. These gases were lost into space. Earth’s

gravity was not strong enough to hold them close to its surface. During

this time, Earth’s internal structure had yet to differentiate into the

solid inner and liquid outer cores. The very young Earth did not have a

magnetic field to protect the atmosphere. Therefore, it was eroded by

the solar wind. The fluid motion in Earth’s iron-rich outer core created

the magnetosphere. After that, the atmosphere was protected.

Astronomers think that the young Sun was about one third dimmer

than it is today. Yet, during Earth’s first 500 million years, its young

hydrosphere did not freeze over. Earth did not turn into a giant snowball.

Many scientists believe that Earth’s young atmosphere was richer in

greenhouse gases. This kept the planet from freezing over. As the Sun

became brighter, the concentration of greenhouse gases declined. They

eventually reached modern levels. This is known as the faint young Sun

paradox.

The interaction between the geosphere and the fluid spheres was vital to

the development of the granite rocks that now make up the continents.

Earth’s young crust was largely made of basalt. Particles that were

weathered from the crust had more silica. Silica is resistant to chemical

and physical attack. Silica-rich sedimentary rocks built up in the oceans.

They later melted in subduction zones. As a result, the melted basaltic

oceanic crust became richer in silica from the added melted sedimentary

rocks. This formed andesitic magma. This magma has less magnesium and

iron than basaltic magma. This less-dense magma was injected into the

continents. It prevented them from future subduction. This is because they

were more buoyant.