Evolution of Earth’s Spheres

GCHS Earth Systems Science

/ Geosphere Includes earth’s Interior

EARLY EARTH – Would have been extremely hot and inhospitable to human and other life forms that currently live on this planet. Over the past 4.5 billion years each of the earth’s spheres has evolved making earth the habitable planet it is today.

Evolution of the Geosphere

THE MOLTEN EARTH - Soon after its formation the earth was completely melted. This melting was due to the decay of radioactive elements in the interior and heat left over from the collisions that formed the earth.

THE LAYERED EARTH

Melting allowed the earth to separate into layers through a process known as differentiation.

As earth melted, denser elements such as iron and nickel sank to become the core. Lighter elements such as silicon and oxygen rose to the surface and became the crust.

Differentiation began about 100 million years after earth formed.

• Slowly the earth cooled from the outside in. Molten rock exposed to the cold temperature of space cooled and began solidifying fairly quickly.

• The first crust was thin and constantly changing due to wide spread volcanism tectonic activity

THE FORMATION OF THE CRUST

Origin and Evolution of Earth’s Hydrosphere

Water molecules were present in the nebula from which the solar system and the earth formed 4.567 billon years ago.

Scientist’s believe that the majority of water on Earth came from two sources:

1) Meteor Impacts and Comet Impacts (about half)

2) Volcanic Outgassing (release of water already trapped inside earth)

The early earth was bombarded by meteorites. These meteorites contained water that became part of the material the made up the earth.

• Volcanic activity released the trapped water to the atmosphere.

• As the earth cooled the water condensed and fell to the ground as precipitation

Evolution of Earth’s Atmosphere

EARTH’S FIRST ATMOSPHERE • Mostly composed of hydrogen and helium. These were the

main elements present in the solar nebula from which the solar system formed

• Earth’s gravity is not strong enough to hold on to these light elements so they eventually drifted off into space

EARTH’S SECOND ATMOSPHERE• The second atmosphere was the result of

outgassing from wide spread volcanic activity. • The early atmosphere was probably rich in

carbon dioxide (CO2), nitrogen (N2), methane(CH4), ammonia (NH3), and water vapor (H2O)

• This atmosphere was void of free oxygen (O2)

FORMATION OF OR OXYGEN RICH ATMOSPHERE• By 3.5 Bya. Simple organisms called cyanobacteria (also

known as Blue –green algae) thrived in the acidic, carbon dioxide rich oceans and released oxygen to the atmosphere. Colonies of these organisms formed reef like structures called stromatolites.

• As life evolved, photosynthesis produced large quantities of oxygen that eventually led to the atmosphere with free oxygen that we have today.

•  Between 2.5 and 1 billion years ago, during the Proterozoic, the amount of free O2 in the atmosphere rose from 1 - 10 %..

• Present levels of O2 were probably not achieved until 500 to 400 Million years ago.

• The present state of the atmosphere is a balanced between life and geological process. The atmosphere is still evolving.

Present Composition of Earth’s Atmosphere

-Present

Present Composition of Earth’s Atmosphere

Earth’s atmosphere continues to evolve. The above graph shows the recent trend in the carbon dioxide (CO2) content in the atmosphere.

STRUCTURE OF THE ATMOSPHERE – The atmosphere is divided intoLayers primarily based on changes on temperature. The majority of the gasesare concentrated in the troposphere.

• For organisms to live, appropriate environmental conditions must exist in terms of temperature, moisture, energy supply, and nutrient availability

• Energy is needed to drive the functions that organisms perform, such as growth, movement, waste removal, and reproduction

• The ultimate source energy for life on earth is the Sun

• During the long history of life on Earth (about 3.8 billion years), organisms have drastically altered the composition of each of the earth’s sphere.

• When life first evolved, the atmospheric concentration of carbon dioxide was much greater than today, and there was almost no free oxygen

• After the evolution of photosynthesis there was a large decrease in atmospheric carbon dioxide and an increase in oxygen

• It was not until oxygen reached similar concentrations to what occurs today (about 21% by volume) that multicellular organisms were able to evolve