P1 - The Earth in the Universe Flashcards
When it first formed, the Earth was completely _____.
Molten (hot liquid)
How old do scientists estimate the Earth to be?
4500 million years old
Why do scientists estimate the Earth to be 4500 million years old?
Because it has to be older than its oldest rocks, which have been found at about 4000 million years old
What is the age of the oldest rocks found on Earth?
4000 million years old
What can studying rocks tell us?
More about the Earth’s structure and how it has changed
In what ways has the Earth’s structure changed? [4 things]
- Erosion
- Craters
- Mountain formation
- Folding
Explain how erosion has changed the Earth’s structure.
The Earth’s surface is made of rock layers, one on top of another. The oldest is usually at the bottom. The layers are compacted sediment, produced by weathering and erosion. Erosion changes the surface over time.
Explain how craters have changed the Earth’s structure.
The Moon’s surface is covered with impact craters from meteors. Meteors also hit the Earth but craters have been erased by erosion.
Explain how mountain formation has changed the Earth’s structure.
If new mountains weren’t being formed, the Earth’s surface would have eroded down to sea level.
Explain how folding has changed the Earth’s structure.
Some rocks look as if they’ve been folded in half. This required huge force over a long time.
Other than rocks, what else can be studied to give further evidence of the Earth’s age?
- Fossils of plants and animals in sedimentary rock layers, which show how life has changed
- The radioactivity of the rocks
How does studying the fossils of plants and animals in sedimentary rock layers help to give further evidence of the Earth’s age?
They show how life has changed
How does studying the radioactivity of rocks help to give further evidence of the Earth’s age?
A rock’s radioactivity decreases over time and radioactive dating measures radiation levels to find out a rock’s age.
What 3 parts make up the main structure of the Earth?
- Thin rocky crust
- The mantle
- The core
Give 3 points about the thin rocky crust that makes up part of the main structure of the Earth.
- Thickness varies between 10km and 100km
- Oceanic crust lies beneath the oceans
- Continental crust forms continents
Give 3 points about the mantle that makes up part of the main structure of the Earth.
- Extends almost halfway to the centre of the Earth
- Has a higher density, and different composition, than rock in the crust
- Very hot, but under pressure
Give 3 points about the core that makes up part of the main structure of the Earth.
- Accounts for over half of the Earth’s radius
- Made of nickel and iron, and has a liquid outer part and a solid inner part
- The decay of radioactive elements inside the Earth releases energy, keeping the interior hot.
Who proposed the continental drift theory?
Wegener
What did Wegener notice that made him propose the theory of continental drift?
He saw that the continents had a jigsaw fit, with mountain ranges and rock patterns matching up.
What did Wegener notice about fossils of the same animals on different continents?
He said that different continents had separated and drifted apart.
What did Wegener claim happened when two continents collided?
They forced each other upwards to make mountains
For what reasons did geologists struggle to accept Wegener’s theory about Continental Drift?
- He wasn’t a geologist so was seen as an outsider
- The supporting evidence was limited
- It could be explained more simply, e.g. a bridge connecting continents had eroded over time
- The movement of the continents wasn’t detectable
a) What finally convinced geologists that Wegener’s theory about Continental Drift was right?
b) Through this ______ ________ process it became an accepted theory.
a) Evidence from seafloor spreading
b) peer review
The Earth’s crust is cracked into several large pieces called what?
Tectonic plates
How are tectonic plates able to float on the Earth’s mantle?
Because they’re less dense
True or False?
Tectonic plates are incapable of moving apart.
False - Tectonic plates are able to move apart, and also towards or slide past one another
What are the lines where tectonic plates meet called?
Plate boundaries
What normally occurs at plate boundaries (the lines where tectonic plates meet)?
Volcanoes, earthquakes and mountain formations
What can often result from earthquakes near coastlines or at sea?
Tsunamis
What is a geohazard?
A natural hazard
Give 2 examples of a geohazard
- Floods
- Hurricanes
What can be done as a precautionary measure to prepare for a geohazard that could strike without warning?
- Buildings in earthquake zones are designed to withstand tremors
- Authorities will often refuse planning permission in areas prone to flooding
The mantle is fairly ____ just below the Earth’s crust. Further down it’s ________.
- solid
- liquid
What causes magma to rise in the mantle?
Convection currents
What can convection currents cause in the mantle?
Rise of magma
How can convection currents cause magma to rise in the mantle?
The currents move the solid part of the mantle and the tectonic plates.
Explain seafloor spreading.
Where tectonic plates move apart, magma reaches the surface and hardens, forming new areas of oceanic crust (seafloor) and pushing the existing floor outwards.
New crust is continuously forming at the crest of an oceanic ridge and old rock is pushed out. This causes seafloors to spread by a few centimetres a year.
True or False?
The earth has a magnetic field. (HT)
True
How often does the magnetic field of the Earth change polarity? (HT)
Every million years
How are rock stripes of alternating polarity formed? (HT)
Seafloor spreading combined with the change in polarity of the Earth’s magnetic field every million years.
Combined with seafloor spreading, what is produced by the polarity change in the Earth’s magnetic field every million years? (HT)
Rock stripes of alternating polarity
How can geologists see how quickly crust is forming? (HT)
By the width of the rock stripes with alternating polarity on the crust of the earth
Where are rock stripes of alternating polarity formed? (HT)
At constructive plate boundaries where plates are moving apart.
What happens when oceanic and continental plates collide? (HT)
The denser oceanic plate is forced under the continental plate
What is it called when an oceanic and a continental plate collide, and the denser oceanic plate is forced under the continental plate? (HT)
Subduction
Explain what is meant by the term subduction. (HT)
When an oceanic and a continental plate collide, and the denser oceanic plate is forced under the continental plate
a) When a denser oceanic plate is forced under a colliding continental plate (subduction), what happens to the oceanic plate? (HT)
b) Where does this occur? (HT)
a) The oceanic plate melts and molten rock can rise to form volcanoes.
b) destructive plate boundaries
Where do mountain ranges form? (HT)
Along colliding plate boundaries as sedimentary rock is forced up by the pressure created in a collision.
Explain in stages how earthquakes occur most frequently at plate boundaries. (3 stages) (HT)
- The plates slide past each other or collide
- Pressure builds up as plates push on each other
- Eventually, stored energy is released and waves of energy spread from the epicentre.
Explain how plate movement is crucial in the rock cycle. (HT)
- Old rock is destroyed through subduction
- Igneous rock is formed when magma reaches the surface
- Plate collisions can produce high temperatures and pressure, causing the rock to fold
- Sedimentary rock becomes metamorphic rock
Earthquakes produce wave motions where?
On the surface and inside the Earth
What is the device used to detect wave motions on the surface caused by earthquakes?
Seismograph
What are the two types of waves generated by an earthquake?
- Primary waves (P-waves)
- Secondary waves (S-waves)
Give 3 points about P-waves (primary waves).
- Travel faster than s-waves
- Can travel through both liquids and solids
- Can travel through the liquid region of the outer core of the Earth
Give 2 points about s-waves (secondary waves).
- Can only travel thruogh solids
- Can’t travel through the liquid ergion of the outer core of the Earth
What kind of waves are p-waves? (HT)
Longitudinal waves
What kind of waves are s-waves? (HT)
Transverse waves
True or False?
P-waves and S-waves travel at the same speeds no matter the density in the rocks. (HT)
False - P-waves and S-waves travel at different speeds in rocks of different density.
P-waves and S-waves travel at different speeds in rocks of different density. Do the waves travel faster or slower if the rock has a high density? (HT)
Faster
P-waves and S-waves travel at different speeds in rocks of different density. Do the waves travel faster or slower if the rock has a lower density? (HT)
Slower
What effect do the boundaries between different types of rock have on p-waes and s-waves?
Changes in speed
What leads to changes in speed in p-waves and s-waves?
The boundaries between the different types of rock
The boundaries between the different types of rock lead to changes in the speed of p-waves and s-waves. What two things could this cause in waves?
Refraction or reflection
Measurements taken from seismographs at different points on the Earth’s surface can be used to give evidence about what?
The structure of the Earth
What can be used to give evidence about the structure of the earth by using measurements at different points on the Earth’s surface?
Seismographs
What provides the heat in the Earth’s core?
The decay of radioactive elements
What evidence do scientists study to obtain information about the Earth’s age?
Fossils of plants and animals, and radioactivity of rock
What type of wave, generated by an earthquake, travels through the liquid outer core of the Earth?
P-waves
In plate movement, old rock is destroyed by which process? (HT)
Subduction
What two factors produce rock stripes of alternating polarity? (HT)
Deep-floor spreading and the changing polarity of the earth’s magnetic field every million years
What are waves?
Regular patterns of disturbance that transfer energy from one point to another without transferring particles of matter.
What are the two types of waves?
- Longitudinal
- Latitudinal