Understanding Planet Earth

how old is Earth

4.54 Ga (bil years)

theories in figuring out Earth’s age - Leonardo da Vinci

• 1500 AD

• measured sedimentation rate in the Po delta, italy

• -200,000 years

theories in figuring out Earth’s age - Archbishop Usher

• 1650 AD

• used Old Testament to create a family tree from Adam and Eve

• 6000 years

theories in figuring out Earth’s age - Benoit de Maillet

• 1748

• observed marine fossils at mountain peaks as he assumed mountains were once under the sea

• - 2.4 Ga (billion years)

theories in figuring out Earth’s age - Georges de Buffon

• 1770

• measured rate of a cannon ball cooling and scaled this up to Earth’s size

• - 75,000 years

theories in figuring out Earth’s age - James Hutton

• 1780

• did not conclude age but said there was ‘no vestige of a beginning’

• over 6,000 years

theories in figuring out Earth’s age - Charles Darwin

• 1859

• calculated erosion rate in Downs, England

• at least 300 Ma (million years)

theories in figuring out Earth’s age - William Thompson, Lord Kelvin

• 1862

• computed the time it took for Earth to cool as they believed it was originally a molten planet

• 20-30Ma

7 (wrong) theories to predict Earth’s age

1. Leonardo da vinci

2. archbishop usher

3. Benoit de maillet

4. Georges de buffon

5. James hutton

6. Charles darwin

7. William Thompson, lord kelvin

3 principles to date Earth’s age

1. uniformitarianism - the physical processes that occur now also happened in the past

2. superposition - each layer must be younger than the one below it

3. original continuity - sediments accumulate in continuous sheets

geological column

correlating where rocks are form to piece together a column that represents Earth

relative vs numerical age

relative - age of a feature relative to another

numerical/absolute - age of feature in years

radioactive decay

• all atoms have the same number of protons in the nucleus

• not all atoms have the same number of neutrons in the nucleus

—> not all atoms have the same atomic weight

• some isotope of an element are stable but others undergo RD that converts them into another element

• RD stated in terms of half life (years) - time needed for HALF of the isotopes to decay

how far away is Earth from our Moon

384,000km

impact of the Moon on Earth

• ocean tides (moon has 2x more influence on tidal patterns than sun)

• stabilises Earth’s rotations - sustains seasons and climate

• lunar cycles

• cultural importance

• gradually slows Earth’s spins

pre Apollo prediction of Moon formation

1. co-accretion - Earth and Moon formed together

2. fission - Earth split off Moon chunk sized

3. capture - Earth captured the Moon

post Apollo prediction of Moon formation

• giant impact - large body called Theia collided with Earth, releasing material to form the Moon

petrology of moon

rock definition

naturally occurring, unconsolidated material comprised of one or more mineral phases

3 types of rock

igneous

sedimentary

metamorphic

igneous rock

• made from lava flow

• effusive eruptions

• Earth’s crust is mainly igneous

sedimentary rock

• comprised of weathered grains of other rock

• forms at/near Earth’s surface

  • cementation of fragments from other rock

  • precipitation of minerals

  • skeletal material in organisms

metamorphic rock

• formed when rocks are subjected to extreme temperatures/pressure and change completely

• leads to growth of new minerals/textures

• happens without melting

importance of sedimentary rocks

• serves as historical geological/biological record of events

• contains the bulk of water and energy sources

• can turn into soil

weathering process

: processes that break up/corrode rock turning it into sediment

physical: breaks rocks into grains/chunks

chemical: alter/destroys minerals when in contact with water solutions or air

plate tectonics

• drives the rock cycle

• lithosphere divided into 15-20 plates of diff size that move in relation to one another

structure of the Earth

crust

oceanic

• basalt (iron, magnesium)

• heavy and dense

continental

• granite (sodium, calcium)

• less dense

—> denser oceanic rock subjects under continental crust

hotspots

: isolated volcanic centres away from plate boundaries

• lies at end of chains of extinct volcanic islands and sea mounts