Dynamic Earth: A Journey Through Earth’s Systems
Theme 2: The Dynamic Earth
The Atmosphere
Earth is a planet characterized by active gases like methane and oxygen, which react rapidly. This dynamic atmosphere absorbs heat from the Earth’s surface, causing expansion.
Liquid Water on Earth
Why does liquid water exist on Earth’s surface?
- Gravity and Atmospheric Pressure: Earth’s gravity maintains atmospheric pressure, limiting evaporation.
- Greenhouse Gases: These gases prevent the hydrosphere from freezing.
Moving water erodes material from highlands to lowlands, where it deposits sediment.
Continental Drift
Alfred Wegener’s theory of continental drift proposed that the continents were once united in a supercontinent called Pangaea around 200 million years ago. Evidence for this includes:
- Geographical: Similar coastlines of continents.
- Paleontological: Matching fossil distributions across continents.
- Geological and Tectonic: Similar rock types, mountain ranges, and geological structures.
- Paleoclimatic: Evidence of past climates across continents.
The Fragmented Lithosphere
Earth’s energy manifests as heat and earthquakes. Seismic and volcanic activity is concentrated along lines, suggesting a fragmented lithosphere composed of large plates.
Plate Tectonics
Plate tectonics explains Earth’s geological history. Heat from the Earth’s core drives convection currents in the mantle, causing the lithosphere to break into plates. Plate collisions create ridges, and oceanic lithosphere is destroyed through subduction.
Soil erosion is caused by the weathering of the Earth’s crust.
Theme 3: The Building Blocks of Life
Composition of Living Matter
Living matter is primarily composed of carbon, oxygen, and nitrogen.
Energy for Life
Life requires energy from chemical reactions involving organic matter. Photosynthesis, carried out by plants, algae, and some bacteria, produces carbohydrates. Cellular respiration then releases the energy stored in these carbohydrates. Organisms are classified as autotrophs (plants) or heterotrophs based on how they obtain organic matter.
The Miller-Urey Experiment
In 1953, Stanley Miller synthesized amino acids from ammonia, water vapor, and methane, simulating the early Earth’s atmosphere.
Panspermia
The panspermia hypothesis suggests that life originated in space. Points for:
- Discovery of organic molecules in nebulae.
- Impacts from space could have brought life to Earth.
- Common characteristics of life suggest a single origin.
Points against:
- No evidence of extraterrestrial life.
- Doesn’t explain the ultimate origin of life.
Evolution
All species on Earth descend from common ancestors, evidenced by fossils. Three types of evidence support evolution:
- Biological (current organisms)
- Paleontological (fossils)
- Molecular genetics
A species is defined as a group of organisms that can reproduce and produce fertile offspring.
Natural Selection
Charles Darwin proposed natural selection, or survival of the fittest, as the mechanism for evolution.
Darwinism and Genetics
Modern genetics explains inheritance and how genes are passed down. Neo-Darwinism, or the synthetic theory of evolution, combines Darwinism with genetics.
Artificial Selection
Humans selectively breed plants and animals with desirable traits, influencing their evolution.
Definitions
Epicenter: The point on Earth’s surface directly above the focus of an earthquake.
Hydrosphere: All the water on Earth’s surface, including oceans, lakes, and rivers.
Autotroph: An organism that produces its own food, such as plants.
Pangaea: The supercontinent that existed millions of years ago.