Structure of the Earth and Plate Tectonics: A Comprehensive Guide

Structure of the Earth

Earth consists of four concentric layers: inner core, outer core, mantle, and crust. The crust is made up of tectonic plates, which are in constant motion. Earthquakes and volcanoes are most likely to occur at plate boundaries.

Inner Core

The inner core is in the center and is the hottest part of the Earth. It is solid and made up of iron and nickel with temperatures reaching 5,500ºC.

Outer Core

The outer core is the layer surrounding the inner core. It is a liquid layer, also made up of iron and nickel. Temperatures are similar to the inner core.

Mantle

The mantle is the widest section of the Earth, with a thickness of approximately 2,900km. It is made up of semi-molten rock called magma.

Crust

The crust is the outer layer of the Earth, a thin layer between 0-60km thick. It is the solid rock layer upon which we live. There are two different types of crust: continental (which carries land) and oceanic (which carries water).

Tectonic Plate Theory

• Continental Fit: The continents seem to fit together like a jigsaw puzzle.
• Structures and Anomalies: Similar geological formations and fossils are found on continents now separated by oceans.
• Volcanoes and Earthquakes Distribution: These events are concentrated along specific belts, often coinciding with plate boundaries.
• Magnetic Anomalies over Ocean Ridges: Alternating patterns of magnetic polarity in the ocean floor provide evidence of seafloor spreading.
• Ages and Distribution of Ocean Floor: The youngest oceanic crust is found near mid-ocean ridges, while older crust is found farther away.
• The Earth is a Thermal Engine: Heat flow from the Earth's interior drives mantle convection and plate movements.

Constructive Boundary

At a constructive boundary, plates move apart due to convection currents inside the Earth.

Destructive Boundary

At a destructive boundary, plates move towards each other. This usually involves a continental plate and an oceanic plate.

Earthquakes

Earthquakes are the result of a sudden release of energy in the Earth's crust that creates seismic waves. They can cause landslides, snowslides, building collapses, and tsunamis.

Volcanoes

Volcanoes can cause landslides, climatic change, environmental consequences, and air traffic problems due to ash and particles injected into the atmosphere.

Mendel's Laws of Inheritance

Mendel's First Law (Law of Segregation)

In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation.

Mendel's Second Law (Law of Independent Assortment)

The different alleles for a trait separate randomly and independently of each other.

Mendel's Third Law (Law of Dominance)

Each pair of alleles segregates during gamete formation. Each gamete contains one allele from each pair.

Basic Genetics Terminology

• Genetics: Study of the patterns of inheritance of specific traits, relating to genes and genetic information.
• Hereditary: Genetic constitution of an individual.
• Gamete: Mature sexual reproductive cell, as a sperm or egg, that unites with another cell to form a new organism.
• Fertilization: Union of male and female gamete nuclei, fecundation or impregnation of animals or plants.
• Zygote: Cell produced by the union of two gametes.
• Character: Characteristic inherited from parents to offspring. This characteristic can be dominant, recessive, or codominant.
• Genotype: The combination of genes of an organism.
• Allele: Each one of the alternatives of a gene; alleles are the variations of the characters.
• Heterozygous: Character with the genotype with two different alleles.
• Homozygous: Character with a genotype containing the same information, the same allele.
• Phenotype: Appearance of a character regardless of the genes.