Chapter 6
Fluvial
River environments that deposit gravel, sand, and mud. Characterized by channels, point bars, and floodplains.
Carl Linnaeus
The “father of taxonomy,” Linnaeus developed a system to classify organisms, hinting at relationships among species.
What Is Evidence for the Hadean?
Zircon crystals: Found in rocks from Western Australia (4.4 billion years old), these are some of Earth’s oldest minerals and indicate crustal formation.
Lunar and meteorite samples: These provide insight into conditions in the early solar system and suggest similar early processes on Earth.
Isotopic studies: Isotopes in ancient minerals offer clues about early differentiation and atmospheric composition.
The Great Oxygenation Event (GOE)
Around 2.4 billion years ago, oxygen produced by photosynthetic cyanobacteria began to accumulate in the atmosphere in significant amounts, causing a shift from an anoxic to an oxygenated environment.
This led to the formation of banded iron formations (BIFs), as iron in the oceans oxidized and settled on the seafloor, creating layers of iron-rich minerals.
Supercontinent Rodinia
Rodinia was a supercontinent that formed around 1.1 billion years ago through the assembly of cratons and began breaking apart around 750 million years ago.
The formation and breakup of Rodinia affected global climate and ocean circulation patterns, possibly contributing to later glaciation events.
Aeolian
Wind-driven environments, such as deserts, producing well-sorted sandstones with large cross-bedding (e.g., dune deposits).
Charles Darwin
Developed the theory of evolution by natural selection, observing how species like the Galapagos finches adapted to different niches.
Greenstone Belts
These are zones of metamorphosed volcanic and sedimentary rocks, often associated with early tectonic activity and mineral deposits. They commonly occur within cratons.
Snowball Earth
1.During the late Proterozoic, a series of severe global glaciations likely covered the planet with ice, known as Snowball Earth events.
Evidence for Snowball Earth includes glacial deposits found at low latitudes and geochemical signals (e.g., shifts in carbon and oxygen isotopes) that suggest widespread ice cover
Role in oxygen production
Photosynthetic microbes gradually released oxygen into the oceans and atmosphere, eventually leading to the oxygen-rich environment that supported more complex life forms.
Clastic Rocks
Formed from the accumulation of fragments of pre-existing rocks. Grain size helps classify them, with sandstone (sand-sized particles), shale (clay-sized particles), and conglomerate (gravel-sized particles) being common examples.
Natural Selection
Darwin’s principle that organisms best adapted to their environments tend to survive and reproduce, passing favorable traits to offspring (“survival of the fittest”).
Shields
Exposed areas of ancient continental crust, mostly composed of Archean rocks. Examples include the Canadian Shield.
Wilson Cycle
The Wilson Cycle describes the cyclical opening and closing of ocean basins due to plate tectonics, involving stages like rifting, passive margin sedimentation, and eventual collision and mountain building.
Oxygenation
The atmosphere became oxygen-rich much later, during the Great Oxygenation Event in the Proterozoic, thanks to photosynthetic organisms.
Chemical Rocks
Form from minerals precipitating directly from water. Common examples include rock salt (from halite) and limestone (precipitated calcite).
Gene Flow
The transfer of genetic material between populations, introducing new traits.
Stromatolites
Fossilized structures formed by cyanobacteria, are among the earliest evidence of life, indicating that photosynthetic organisms were present around 3.5 billion years ago.
Laurentia
Laurentia was an ancient landmass that formed the core of present-day North America. It is made up of various cratons and greenstone belts that coalesced over billions of years.
Fossil Record
Fossils provide a chronological record of life on Earth, showing changes in organisms over millions of years. Transitional fossils reveal intermediate forms, supporting gradual changes.
Guadalupe Mountains Geological Story
Permian Period Origins: Around 260-270 million years ago, the region was submerged under a shallow sea called the Delaware Basin. This basin allowed the formation of a massive reef, known as the Capitan Reef, composed primarily of sponges, algae, and other reef-building organisms.
Capitan Reef Formation: The reef structure accumulated layers of calcium carbonate, creating thick deposits of limestone and dolostone as organisms thrived in the warm, shallow marine environment.
Uplift and Exposure: Following the end of the Permian Period, tectonic forces uplifted the reef complex, exposing the fossilized reef structures we see today in the Guadalupe Mountains.
Cave Formation: Later, sulfuric acid dissolution carved out the famous caves, like Carlsbad Caverns, within the limestone. This unique process differs from typical limestone cave formation and showcases the complexity of the region’s geology.
Modern Significance: Today, the Guadalupe Mountains offer a rare and well-preserved glimpse into ancient reef ecosystems and provide insight into the Permian environment, one of the most significant natural archives of this geologic period.
What Evidence Supports Evolution?
Fossil Record: Fossils provide a chronological record of life on Earth, showing changes in organisms over millions of years. Transitional fossils reveal intermediate forms, supporting gradual changes.
Comparative Anatomy: Structures that are similar in different species (homologous structures) suggest a common ancestry (e.g., the limb bones in vertebrates).
Parallel, Divergent, and Convergent Evolution: Patterns like convergent evolution (independent evolution of similar traits) and divergent evolution (accumulation of differences leading to speciation) explain variations and adaptations.
Genetics: DNA comparisons reveal similarities among species, showing that closely related species have more genetic overlap.
Biogeography: The geographic distribution of species reflects evolutionary histories (e.g., unique species on isolated islands like the Galapagos).
Embryology: Similar developmental patterns in embryos suggest a common ancestor.
Molecular Evidence: Proteins and DNA sequences help trace evolutionary lineages and divergence times.
Key events during the Hadean
Formation of the Earth’s core and crust.
Gradual differentiation of elements, with heavier elements sinking to form the core and lighter elements rising to form the crust and mantle.
Emergence of the early atmosphere and hydrosphere, largely through volcanic outgassing and possibly comet impacts.
Significance of the Ediacaran Fauna
The Ediacaran fauna represent an important step in evolution, showing the beginnings of multicellularity, tissue differentiation, and large body size.
They are rare and only preserved in a few locations due to the absence of hard parts and the need for specific depositional conditions.
Deltaic
River-dominated environments where sediments are deposited at the mouth of a river entering a body of water. Expect silts, clays, and sands forming topset, foreset, and bottomset beds.