Earth's Formation and Dynamic Processes

Origin of Life on Earth

The early ocean contained organic molecules: lipids, amino acids, carbohydrates, forming an organic soup. Coacervates formed, which were (proto) lipid droplets surrounded by RNA. These coacervates acquired the ability to nurture and make copies of themselves, therefore forming the first simple cells: prokaryotes and heterotrophic cells that were already anaerobic. These cells contained RNA.

Many cells died from lack of food, and others, through mutation, were able to make their own food with H₂O + CO₂ and energy from the sun. These were autotrophic prokaryotic cells. They produced oxygen, which combined with other elements over the course of nature. The ozone layer formed, protecting living things from ultraviolet radiation.

Theory of Plate Tectonics

In the mid-twentieth century, the theory of plate tectonics was proposed, based on continental drift, paleomagnetism, and seafloor spreading. The theory proposes that the lithosphere is a rigid and fragmented layer, and these fragments are called lithospheric plates. The lithospheric plates move because the asthenosphere flows through convection currents that occur when hot material rises and cools, then descends, acting like conveyor belts.

Major seismic and volcanic activity is located within the boundaries of the plates. This theory explains the formation of the lithosphere: crust is created at the ridges and destroyed at subduction zones.

Earth's Internal Structure

The lithosphere includes the crust and the upper part of the upper mantle, down to the asthenosphere. The asthenosphere is made up of semi-molten materials.

The mesosphere includes the lower part of the upper mantle and the lower mantle. The endosphere covers the entire core.

Types of Plate Boundaries

Plate boundaries are where lithospheric plates interact. There are three main types of movement:

Divergent Boundaries

These are located at oceanic ridges. Edges are constructive because they form new oceanic lithosphere.

Convergent Boundaries

These involve movement toward each other, where one plate is typically destroyed.

Oceanic-Continental Convergence (Subduction)

An oceanic plate collides with a continental plate. Peri-oceanic mountain ranges like the Andes Cordillera are formed.

Oceanic-Oceanic Convergence

An oceanic plate collides with another oceanic plate, forming island arcs.

Continental-Continental Convergence (Obduction)

A continental plate collides with another continental plate, forming intercontinental mountain ranges like the Himalayas.

Transform Boundaries

These involve lateral gliding motion, where one plate moves horizontally past another. This is a passive edge because lithosphere is neither created nor destroyed, as seen in the San Andreas Fault.

Major Oceanic Ridges

Oceanic ridges are huge underwater mountain ranges where oceanic lithosphere is created. There are three major types:

Mid-Atlantic Ridge

Crosses the Atlantic from north to south.

Indian Ridge

Travels from South Africa past Madagascar, rises to the Gulf of Aden, reaches Australia, and joins the East Pacific Rise.

East Pacific Rise

Parallels South America and is subducted below North America.