L3. Origins: Plate Tectonics Flashcards
How do describe evolution of the earth?
Geological Timescales
- measured in millions or billions of years (Eons->Eras->Periods)
- Periods based on rock/fossil record and corresponds to changes in the Earth’s climate, surface, and or major forms of life
How do we keep time?
Absolute dates come from radiometric dating of igneous rocks
Relative dating comes from relationships between rocks
Three types of rocks
Igneous: formed through cooling of magma
Sedimentary: formed from chemical precipitates or fragments of earlier formed rocks
Metamorphic: formed form application of heat and pressure to either igneous or sedimentary rocks
How do we know how old a rock is?
Absolute dates come from radiometric dating, observing the radioactive decay of an isotope
Relative dates come from relationship between rocks
What is an isotope
Versions of atoms with the same number of protons but different numbers of neutrons in them. Differ depending on element
How does Radioactive dating work?
Isotope decay at a consistent rate, which can be measured. The measurement gives us the rate of decay also known as the half life. Basically means when the reaching the half life, half of the original element will be gone transformed into another isotope.
The original unstable radioactive element is called the parent, and the stable isotope you end up with is called the daughter. You can compare ratio of parent to daughter atoms assuming the rock is a closed system (the decay rates).
How does relative dating work?
- Inferring a sequence in which older to younger events recorded in rocks occur.
- This works because in sedimentary rocks the older rocks are the layers at the bottom and the younger rocks are the ones above them. This happens due to the principle of superposition.
- Important to remember that we cannot use the thickness of sedimentary layers to estimate how much time any layer represents because layers can be effected by many processes.
Principle of Superposition
Sedimentary rock is produced from the gradual accumulation of sediment on the surface. Therefore newer sediment is continually deposited on top of previously deposited or older sediment
Fossils and Relative Dating
Organisms fossils remains turn to fossils and stay in sedimentary rock. Geologists study the order in which fossils appear and Diaspora . They can help match rocks that same age even when found far apart. Fossils are most abundant in marine sedimentary rocks
When did the earth form
4.54 billion years ago out of a solar nebula. Gravity pulled gas and dust to form the planet.
- nebula: swirling cloud made up of bits and pieces left over from old stars that have exploded
Goldilocks Zone
habitable zone around a star where the temperature is just right for liquid water to exist on a planet (Includes Earth and Mars)
Hadean Eon (4.54 Ga - 4.0 Ga)
- hell-like conditions (initially molten)
- constantly bombarded by asteroids and comets which melted earth surface (magma ocean) causing iron heavy materials to sink and create the center of the earth
- moon formed when a small planet collided with the earth and most of its mass joined the earth. Small amount of mass was ejected and went into orbit around the earth becoming the moon.
- by the end of Hadean, earth cooled (steam in the atmosphere cooling and falling as rain) enough for rocks to form. Oceans from the rain formed and first continents begin to form
Earliest piece of planet’s crust
Zircon crystals from Western Austrailia dated to 4.4 billion years
- suggests that within the first 100 to 200 million years of our planet, there was enough cooling to form a crust
- radiometric dating indicates that zircon was most likely formed in a cool wet process at the Earth’s surface
Archean Eon (4.0 Ga - 2.5 Ga)
- liquid water was present
- First evidence of life
- onset of plate tectonics
What is plate tectonics
All of crust on Earth moves around like floating slabs of rock on top of hot mushy rock in the mantle. The earth is chewing itself up, melting itself down, and making itself anew
mantle: hotter part of the Earth between us and the Earth’s iron core
Continental drift
- first proposed by Alfred Wegener in 1915
- the idea that Earth’s continents have moved over geologic time relative to each other, thus appearing to have “drifted” across the ocean
- explains why life looks similar across continents
- wasn’t believed for a long time
Evidence for continental drift
Fossil evidence
- supports theory
- if this wasn’t the case Darwin would have been wrong a breeding pairs would have to swim to each continent
Geological evidence
- same age rock outcrops on separate continents (South America and West Africa) fit into each other
Structure of the Earth
3 layers
- Core: iron, solid inner-core and liquid outer-core which is the source of earth’s magnetic field
- mantle: very hot rocks rich in silicon and oxygen, behaves plastically
- crust: cooler and stiffer rocks
Oceanic crust vs. Continental crust
oceanic: thin, dense, and young
continental: thick, Buoyant, and mostly old
Plate tectonics
- Earth’s crust is divided into 12 major plates which move in various directions.
- Plate motions makes them move (collide, pull apart, or scrape against each other). Convection currents in the mantle drive plate tectonics (cycle of cooling and warming creates motion on top of hot mass). Similar to a giant conveyor belt. Occur on the order of a few cm per year
- Interactions cause earth structures (volcanos, mountains, ocean trenches)
Plate Boundaries
plate boundaries: zones of contact between plates
- Don’t correspond to countries!!
- materials are never created or destroyed
Divergent Boundaries
Divergent: plates moving apart (rifts)
- space created can be filled with new crustal material sourced from magma below
- happens often in ocean and is called “mid-oceanic ridges” (underwater mountain systems). This is where black smokers can be found. Organisms at these vents get their energy from the vent itself.
- ex. happening to Iceland currently
Convergent Boundaries
Convergent: plates colliding
- usually the denser plate is subducted underneath the less dense plate. The plate that goes under is eventually melted and destroyed
- 3 types:
continent-continent collision: creates mountain ranges
continent-ocean collision: creates mountain ranges
ocean-ocean collision: creates trenches
Transform Boundaries
Transform: Plates slide pass one another
- causes stresses and breaks (earthquakes).
- Places that the breaks occur are called fault lines
Plate tectonics and the evolution of life
Affect geography which could in turn affect food supply, climate, and diversity of life
ex. create or destroy niches, form physical barriers
Pangea
Supercontinent that assembled from earlier continents approximately 335 million years ago, and it began to break apart about 175 million years ago
Plate tectonics and biodiversity
Pangea allowed terrestrial organisms to migrate across all the continents and were only limited by their biotic potential. Then it separated creating physical barriers and evolution occurred.
New habitats created due to change in biotic and abiotic factors such as climate (temperature and moisture)
Has been on of the main driving forces promoting the biodiversity of organisms!!! The evolution of life is directly connected to the evolution of earth.
Plate tectonics and weather
Weathering: the breakdown of minerals in rocks at or near Earth’s surface, releasing nutrients. Caused by chemical and physical interactions with air, water, and living organisms
Nutrients are very important for life on earth. May be a relationship with increased nutrients in the oceans and bursts of evolutionary change
Plate tectonics and habitability
Helps regulate that planet’s temperature, recycles nutrients and many other important functions
Is it necessary for habitability and complex life? S
