Earth Science Essentials: Sun, Earth Structure, Plate Tectonics and Geologic Time

Sun, Earth and Atmosphere Basics

Sun = hydrogen-helium.

Earth composition = magnesium, silicon, oxygen, nickel, iron and sulfur.

Translation = movement of the Earth around the Sun, which describes the days and the 365 days and 6 hours of the year, in the opposite direction to the clock hands.

Rotation = movement of the Earth on its own axis. It completes a rotation every 24 hours, which produces day and night and leads to the climatic seasons of the north and south hemispheres.

Atmosphere = troposphere, stratosphere, mesosphere, exosphere, thermosphere, hydrosphere and geosphere.

Weather vs. climate

• Climate = set of average values of atmospheric conditions that characterize the weather of a region.
• Weather = meteorological conditions that occur at a specific moment.

Earth's Internal Structure

Dynamic and geochemical differences: the geochemical classification distributes the layers according to their chemical composition, while the dynamic classification distinguishes them by their mechanical behavior (stiffness).

Mid-ocean ridge = underwater mountain range.

Dynamic and Geochemical Model

• Lithosphere (crust)
• Upper mantle: asthenosphere
• Lower mantle: mesosphere
• Outer core
• Inner core

The Sun and Its Layers

• Core
• Radiative zone
• Convective zone
• Photosphere
• Chromosphere
• Corona

Volcanoes

• Main crater
• Secondary cone
• Volcanic crater
• Focus
• Fumarole
• Geyser

Atmospheric Characteristics and High Temperatures

• Troposphere: 0 to 15 km, where weather phenomena occur, with a temperature drop of 6.5 °C per km.
• Stratosphere: up to 45 km, contains the ozone layer.
• Mesosphere: up to 80 km, where meteorites usually burn up, with temperatures down to -80 °C.
• Thermosphere: up to 500 km, where X-rays and gamma rays arrive, with temperatures up to 1500 °C.
• Exosphere: from 1000 km outward, the outermost atmospheric zone.

Continental Drift

Continents are on the move. Evidence from photographs and space probes confirms that movement. Wegener proposed the idea of continental drift in 1910.

Wegener's Theory

1. At first, there was only one large landmass, Pangea, surrounded by a single ocean, Panthalassa.
2. Pangea broke apart due to various forces, and the loose masses drifted west and separated.
3. Over time, these masses reached their current positions as the continents we know today.

Plate Tectonics

The Earth's rigid outer layer is made of plates that float on magma. The magma moves in a continuous, cyclic motion of rising and sinking, known as convection currents. Where plates move apart they are divergent boundaries, and where they collide they are convergent boundaries.

Continental vs. Oceanic Crust

• Continental crust: about 3,800 million years old, thicker and less dense.
• Oceanic crust: more recent, about 180 million years old, denser.

Three major ridges: Pacific, Indian and Atlantic, plus the Antarctic ridge.

Volcanic eruption types: Hawaiian, Vulcanian, Peléan and Strombolian.

Light-Years and Astronomical Units

• 1 light-year = 9.5 × 10¹² km
• 1 AU = 150 × 10⁶ km

Conversion (AU, km, light-year): 1 light-year × 9.5 × 10¹² km = 9.5 × 10¹² km; 9.5 × 10¹² ÷ 150 × 10⁶ = 6.3 × 10⁴ AU.

Palaeontology and Earth's History

Palaeontology is the science that studies the history of life.

Stratum = one of the sedimentary layers. These are materials transported by the erosion of internal and external agents and deposited in rivers and seas. These sediments form parallel, horizontal layers.

Fossils = remains or traces of organisms. A geologist and age determination can establish how old the rock containing them is.

Internal / external agents: volcanoes, earthquakes / water, wind.

Geologic Time Scale

• Precambrian: Earth formed about 4,600 million years ago through the condensation of cosmic dust. The first fossils are bacteria.
• Paleozoic: plants and animals appear, including gymnosperms, trilobites (marine invertebrates), fish, vertebrates, reptiles and amphibians.
• Mesozoic: gymnosperms and angiosperms appear; dinosaurs, birds and mammals (such as Archaeopteryx) emerge. Fossils include mollusc shells (ammonites, belemnites), and the Atlantic and Indian oceans begin to form.
• Cenozoic (Tertiary): mammal expansion; fossils include Nummulites and angiosperms; continents separate, and the Himalayas and Alps form.
• Quaternary: extinction of many mammals, glaciers, and animal migrations.