Earth’s Dynamic Systems: Atmosphere, Hydrosphere, Lithosphere
Earth’s Dynamic Systems
The Earth is a dynamic planet with an atmosphere, hydrosphere, and lithosphere. The composition of the atmosphere has changed greatly over Earth’s history and continues to do so. Nitrogen makes up 78%, and oxygen a significant percentage, with minority gases also present. Some gases, such as water vapor, carbon dioxide, and methane, control the climate and are essential for life as greenhouse gases. The hydrosphere and atmosphere continually exchange matter and energy through the water cycle.
The atmosphere and hydrosphere also modify the lithosphere. Water and wind erode the lithosphere, transporting material and depositing it in other areas. Solar heat, the gravitational pull of the moon and sun, and gravity drive these phenomena. Landforms are continuously modified by external forces, such as wind and water (seas, rivers, glaciers), through erosion and sedimentation.
The Earth’s Interior
What do we know about the composition, structure, and internal energy of the Earth? After millions of years of erosion, the Earth should be completely flat. However, volcanoes and earthquakes, driven by internal geological forces, also alter the landscape.
Composition
Density: mass / volume
- Average density of surface rocks: 2.2 g/cm3
- Average density of Earth: 5.5 g/cm3
Conclusion: The planet is not homogeneous. The Earth’s interior must contain much denser material than the surface.
Structure
Analysis of seismic waves allows us to understand the Earth’s internal structure. Seismic waves change direction and speed when transitioning between layers. S-waves are slower than P-waves and cannot travel through fluids.
- Crust (0.5%): Silicate rocks, metals.
- Mantle (44.5%): Mostly silicates, some metal oxides.
- Gutenberg Discontinuity (35%): Outer core: liquid iron and nickel. The movement of these molten materials helps produce Earth’s magnetic field.
- Lehmann Discontinuity (20%): Inner core: solid iron and nickel. It experiences 3 million times the atmospheric pressure and a temperature of 6100 ºC, similar to the sun’s surface. It has been studied through the propagation of seismic waves.
Wegener and Continental Drift
In 1912, German meteorologist Alfred Wegener proposed that millions of years ago, the continents were joined as a supercontinent called PANGEA. This large landmass broke up into pieces that moved on the ocean floor, leading to the continents as we know them today.
Evidence for Continental Drift
- Geography: The coastlines of some continents fit together remarkably well.
- Paleoclimate: Remnants of glaciers in Brazil and Congo, and coal deposits in Greenland.
- Biological: Identical land animals that cannot swim are found on either side of the Atlantic.
- Paleontological: Fossils of similar animals and plants are found on both coasts bordering the Atlantic Ocean.
- Geological and Tectonic: If the continents are joined, the types of rocks and chronologies of major mountain ranges would have physical continuity.
Wegener called his theory the THEORY OF CONTINENTAL DRIFT. Although he provided supporting evidence, he could not explain the force capable of moving such large landmasses, so scientists of his time did not accept it.
Oceanographic Evidence
After World War II, mapping of the ocean floor revealed ridges with volcanic activity, dividing the great oceans. In the middle of these ridges is a central depression (Rift Valley), and sediments in this area are minimal.
Paleomagnetism Evidence
Paleomagnetism tests show that as lava emerges in the mid-ocean ridges, minerals with ferrous elements align with the Magnetic North Pole. Studying the paleomagnetism locked into rocks revealed inconsistencies, unless the landmasses had moved, providing further evidence of continental drift. In the 1960s, several researchers completed and corrected Wegener’s theory.