L3. Origins: Plate Tectonics

Question 1

How do describe evolution of the earth?

Answer 1

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

Question 2

How do we keep time?

Answer 2

Absolute dates come from radiometric dating of igneous rocks

Relative dating comes from relationships between rocks

Question 3

Three types of rocks

Answer 3

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

Question 4

How do we know how old a rock is?

Answer 4

Absolute dates come from radiometric dating, observing the radioactive decay of an isotope

Relative dates come from relationship between rocks

Question 5

What is an isotope

Answer 5

Versions of atoms with the same number of protons but different numbers of neutrons in them. Differ depending on element

Question 6

How does Radioactive dating work?

Answer 6

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).

Question 7

How does relative dating work?

Answer 7

• 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.

Question 8

Principle of Superposition

Answer 8

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

Question 9

Fossils and Relative Dating

Answer 9

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

Question 10

When did the earth form

Answer 10

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

Question 11

Goldilocks Zone

Answer 11

habitable zone around a star where the temperature is just right for liquid water to exist on a planet (Includes Earth and Mars)

Question 12

Hadean Eon (4.54 Ga - 4.0 Ga)

Answer 12

• 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

Question 13

Earliest piece of planet’s crust

Answer 13

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

Question 14

Archean Eon (4.0 Ga - 2.5 Ga)

Answer 14

• liquid water was present
• First evidence of life
• onset of plate tectonics

Question 15

What is plate tectonics

Answer 15

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

Question 16

Continental drift

Answer 16

• 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

Question 17

Evidence for continental drift

Answer 17

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

Question 18

Structure of the Earth

Answer 18

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

Question 19

Oceanic crust vs. Continental crust

Answer 19

oceanic: thin, dense, and young

continental: thick, Buoyant, and mostly old

Question 20

Plate tectonics

Answer 20

• 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)

Question 21

Plate Boundaries

Answer 21

plate boundaries: zones of contact between plates
- Don’t correspond to countries!!
- materials are never created or destroyed

Question 22

Divergent Boundaries

Answer 22

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

Question 23

Convergent Boundaries

Answer 23

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

Question 24

Transform Boundaries

Answer 24

Transform: Plates slide pass one another
- causes stresses and breaks (earthquakes).
- Places that the breaks occur are called fault lines

Question 25

Plate tectonics and the evolution of life

Answer 25

Affect geography which could in turn affect food supply, climate, and diversity of life
ex. create or destroy niches, form physical barriers

Question 26

Pangea

Answer 26

Supercontinent that assembled from earlier continents approximately 335 million years ago, and it began to break apart about 175 million years ago

Question 27

Plate tectonics and biodiversity

Answer 27

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.

Question 28

Plate tectonics and weather

Answer 28

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

Question 29

Plate tectonics and habitability

Answer 29

Helps regulate that planet’s temperature, recycles nutrients and many other important functions

Is it necessary for habitability and complex life? S