Earth's Geologic Time, Structures, and Rocks: A Study Guide

Geologic Time Scale (GTS)

Represents the interval of time occupied by the geologic history of the Earth. It provides a meaningful time frame within which events of the geologic past are arranged.

Petrology

Branch of geology that deals with origins, composition, structure, and classification of rocks.

Stratigraphy

Study of rock layers (strata) that involves layering (stratification).

Paleontology

Study of life before the Holocene Epoch, involving studying fossils and evolution.

Precambrian Eon

Includes the Hadean and Archean Era, spanning 88% or roughly 4.1 billion years.

Hadean Era

Considered the 'Chaotic Eon', it stretched from about 4.6 - 3.8 billion years and lasted for 800 million years.

Archean Era

Longest period in Earth's history, stretching from about 3.8 - 2.5 billion years and lasting for 1.3 billion years.

Oxygenation of the atmosphere

A significant change during the Archean Era that marked the origin and diversification of eukaryotic life.

Phanerozoic Eon

Consists of three eras: Paleozoic, Mesozoic, and Cenozoic Era.

Paleozoic Era

A period of significant biological development that began with an abundance of marine invertebrates like trilobites and brachiopods.

Mesozoic Era

The early Mesozoic era saw the formation of several continents and significant changes in plant and animal life.

Cenozoic Era

Current era during which mountains were uplifted and new life forms started appearing.

Relative Dating

Places events or rocks in their chronological sequence or order of occurrence without knowing their actual age.

Absolute Dating

Determines actual ages of rocks and events.

Stromatolites

Structures formed by the activity of microbial mats, which covered shorelines during the Archean Era.

Marine life development

Key evolutionary milestone during the Paleozoic Era where marine life developed shells.

First air-breathing amphibians

Adapted to life on land during the Paleozoic Era.

Dinosaurs

Believed to be descendants of primitive reptiles that had survived from the Paleozoic Era.

Fossilized bones of the biggest dinosaur

Found in Argentina during the Mesozoic Era.

Volcanic activity

Widespread during the Cenozoic Era, forming immense flows of lava and basalt.

Glaciers

Covered the Northern Hemisphere towards the end of the Cenozoic Era.

Earliest records of humans

Included stone tools during the Cenozoic Era.

Decay rate of radioactive isotopes

Method used in absolute dating.

Principle of Original Horizontality

Sedimentary rocks are deposited in horizontal layers.

Principle of Superposition

Bottom layer is oldest; higher layers are younger.

Principle of Cross-cutting Relationships

Features cutting across rocks are younger.

Principle of Inclusion

Fragments within a rock are older than the rock itself.

Carbon Dating

A method used in geology to determine the age of organic materials.

Fossil

A remnant or trace of past organisms.

Classification of Fossils

Fossils are classified based on their formation.

William Smith

Discovered the principle of fossil succession.

Principle of Fossil Succession

Fossils succeed one another in a definite and determinable order; any time period can be recognized by its fossil content.

True Form Fossils

Entire organisms preserved in materials.

Mold Fossils

Hollow impressions of organisms in rock.

Cast Fossils

Mold fossils filled with minerals.

Trace Fossils

Impressions showing activities like footprints and nests of animals.

Index Fossils

Used in geology to correlate rocks of similar age and are associated with a particular span of geologic time.

Ammonites

The most widely used index fossils, abundant and easily identified through levels.

Core

The innermost layer of the Earth, consisting of an inner solid core and an outer liquid core.

Lehmann Discontinuity

The boundary between the outer and inner core.

Mantle

The largest and thickest layer of Earth, made up of molten rocks called magma.

Gutenberg Discontinuity

Detected between the Earth's lower mantle and the outer core as observed by changes in seismic waves.

Moho Discontinuity

The boundary that separates the upper mantle from the Earth's crust, noted by a sudden increase in seismic velocity.

Lithosphere

The solid outer section of the Earth, including the entire Earth's crust and the rigid upper mantle.

Plate Tectonic Theory

Explains the large-scale movements of plates that drift sideways at the rate of 12 cm per year.

Boundary

The border between tectonic plates.

Tectonic Plates

Continents have moved by riding on tectonic plates.

Asthenosphere

The layer that lies below the lithosphere (100 km to 250 km) with rocks that have little strength and are easily deformed.

Continental Crust

The thicker type of crust that lies on top of the mantle, characterized by high elevation.

Oceanic Crust

The thinner type of crust that lies on top of the mantle, characterized by being dark-colored and basaltic.

Repetti Discontinuity

The boundary located between the Earth's upper mantle and lower mantle.

Conrad Discontinuity

Marks the transition between the upper and lower continental crust.

Troposphere

The lowest atmospheric layer, containing 80% of the atmosphere's mass and most of its water vapor and weather phenomena, extending from the Earth's surface to about 12 km.

Tropopause

The boundary at the top of the troposphere where temperature stops decreasing.

Stratosphere

The second lowest layer of the Earth's atmosphere, extending from the top of the troposphere at 12 km to the stratopause at 50 km.

Stratopause

The upper boundary of the stratosphere where temperatures stop rising.

Mesosphere

The third layer of the atmosphere, extending from the stratopause at 50 km to the mesopause at around 80 km, characterized by decreasing temperature with increasing altitude.

Mesopause

The boundary at the top of the mesosphere where temperature stops decreasing.

Thermosphere

The second highest layer of the Earth's atmosphere, extending from the mesopause at 80 km to the thermosphere at around 700 km, where temperatures can rise to as high as 1500°C.

Ionosphere

Part of the thermosphere (80-550 km above Earth) containing highly-ionized gases created when UV radiation strips electrons from nitrogen and oxygen atoms.

Kennelly Heaviside Layer

The layer of the ionosphere that reflects radio waves back to Earth.

Aurora

Natural light display in the sky, typically seen in high-latitude regions, caused by ions interacting with air molecules.

Aurora Borealis

Also called northern lights, a type of aurora seen in the northern hemisphere.

Aurora Australis

Also called southern lights, a type of aurora seen in the southern hemisphere.

Exosphere

The outermost layer of the Earth's atmosphere, extending from about 700 km to 1000 km above sea level.

Exosphere

The layer of Earth where most of the orbiting satellites and low density elements like hydrogen and helium are found.

Ocean

A body of saltwater with almost no boundaries and has limitless volume.

Sea

Part of an ocean that is partially surrounding a landform.

Island Sea

A sea that totally surrounds a landform.

Salinity

The proportion of dissolved salts to pure water, expressed in parts per thousand.

Volcanic Outgassing

The process during which large quantities of water and gases are emitted to the Earth's surface during volcanic eruptions.

Saltwater

Accounts for 97.5% of water on the Earth's crust, coming from oceans and midland seas.

Freshwater

Only 2.5% of the world's water, most of which is locked in glaciers, groundwater, and in lakes and river systems.

Coastal Zone

The region in which the sea bottom is exposed during low tide and is covered during high tide.

Pelagic Zone

Located seaward of the coastal zone's low tide mark, always covered with water.

Neritic Zone

Lies above the continental shelf, beginning from the low tide mark outward from the seashore and extending to a depth of 200 m.

Oceanic Zone

Extends from the edge of the continental shelf, over the continental shelf, and over the ocean floor, characterized by zero visibility.

Epipelagic Zone

Also known as the sunlight zone (0 to 200 m), it gets a lot of sunlight, resulting in an abundance of aquatic plants.

Mesopelagic Zone

Also known as the twilight zone (200 to 1000 m), characterized by dim light due to limited sunlight.

Bathypelagic Zone

Also known as the midnight zone (1000 to 4000 m), does not receive any sunlight, and animals that live here lack eyes.

Abyssopelagic Zone

Also known as the abyss (4000 to 6000 m), described as deep sea, with most animals being invertebrates.

Hadalpelagic Zone

Also known as trenches (6000 to bottom), the deepest part of the ocean, mostly found in deep water trenches and canyons.

Biosphere

Contains the entirety of Earth's living things, integrating all living things and their relationships with the lithosphere, hydrosphere, and atmosphere.

Zone of Life

Another term for the biosphere, referring to the global ecological system of all living things.

10 Percent Rule

From the autotrophs to the predators, you divide by 10. But from the predators to the autotrophs, you multiply by 10.

Autotrophs

Organisms that make their own food from inorganic sources via photosynthesis or chemosynthesis, forming the foundation of the food chain.

Examples of Autotrophs

Plants, algae, and cyanobacteria.

Trophic Level

A specific step in a food chain or web that defines 'who eats whom' and how energy flows.

Producers

Organisms that occupy the first trophic level.

Primary Consumers

Herbivores that occupy the second trophic level.

Secondary Consumers

Carnivores that eat herbivores and occupy the third trophic level.

Biomes

The world's major communities classified according to the predominant vegetation and characterized by the adaptations of organisms to a particular climate.

Aquatic Biomes

Includes freshwater (ponds, lakes, rivers, etc.) and marine (ocean, estuaries, etc.) biomes.

Forest Biomes

Includes tropical, temperate, and boreal forests, each with distinct features dominated by trees.

Grassland Biomes

Characterized by the dominance of grasses.

Desert Biomes

Characterized by low rainfall (less than 50 cm/year) and specialized vegetation and animals adapted to its conditions.

Tundra Biomes

The coldest of all biomes, with low biotic diversity and simple vegetation structure.

Biogeochemical Cycle

The movement of substances through the biosphere, tracking elements from nonliving reservoirs through food chains and back.

Nitrogen Cycle

The process involving nitrogen gas (N₂) fixation, nitrification, and denitrification, crucial for converting atmospheric nitrogen into usable compounds.

Nitrogen Fixation

The process of converting atmospheric N₂ into usable compounds, primarily by terrestrial microorganisms.