week 1 2 Universe and earth strucutre

Earths orbital configuration controls what?

climate and habitability

earths orbit around the sun

ecliptic

tilt

23.45 degrees perpendicular to the ecliptic (why we have seasons)

North tilti towards sun

summer solstice (june 21)

south tilt towards sun

winter solstice

precession

• slow movement of the axis of a spinning body around another axis due to a torque

• polestar changes : 26k yrs

• gravity-induced, slow, and continuous change in the orientation of an astronomical body's rotational axis

Eccentricity

• currently 0.016

• causes 6.4% annual variation in solar radiation

• varies over 100,000-400,000 yr cycles

• a dimensionless number measuring how much an orbit deviates from a perfect circle, ranging from 0 (perfect circle) to just under 1

Perihelion

earth closest to sun

Aphelion

earth furthest away from sun

Milankovitch cycles

• long-term, natural variations in Earth's orbit and axial tilt

• change the amount and distribution of solar radiation received, influencing climate patterns like ice ages over thousands of years

• Contoled the formation of glaciers

Northern hemisphere ice growth

• low obliquity (low seasonal contrast)

• northern hemisphere summers during aphelion (cold summers in the north)

• high eccentricity

Northern hemisphere ice melt

• High obliquity (high seasonal contrast)

• northern hemisphere summers during perihelion (hot summers in the north)

• high eccentricity

key roles of the moon

• stabilise angle of axial tilit: 22.1-24.5 (mars chaotically tilits 0-60)

• generates the lunar tides slows earths rate of rotation

obliquity

tilt

Neap tides

when moon and sun at 90 degrees

spring tides

when moon and sun aligned

intertidal zone

dynamic area of the seashore between the high tide and low tide marks, constantly exposed to air and submerged by water

key evolution for land-walking animals

perigee

moon closest to earth

apogee

moon furthest away from eath

moons orbital plane

inclined about 5.2° from the ecliptic

lunar eclipse

earth shadows moon

needs to be a new moon

solar eclipse

moon passes infront of sun

only a small spot on earth will see it

has to be full moon

stars formation:

when outward pressure from nuclear fusion of H to He balances gravitational collapse

Stellar nucleosynthesis

H to He stop at Fe-56

Rare earth factor

the crucial role rare earth elements have

galactic habitable zone

• high metality - likely to have habitable life

small stars < 0.33 M(sun)

becomes a white dwarf

large stars 10x size of sun bigger

red giant phase

Nebular theory

• Shockwave: trigger instability of nebula

• collapse under own gravity

• gravitational potential energy→ kinetic energy → heat

• as size decrease rotate faster (conservation of angular momentum )

• trigger star formation

• sun forms centre of disk

• dust→ pebbles→ rocky planets form and planetestimals

• moon formed by another planet hitting earth

What changes with depth

• pressure (P) - weight of overlaying rock increases

• temp - heat generated in earths anteriror - radiocativity

• temperature increase

Geothermal gradient

rate at which Earth's temperature increases with depth

determined by tetonic setting

P waves

compressed (solid and liquid)

S waves

shear - travel through solid but not liquid

2 types of earthquakes - solid earth (P and S waves)

seismological evidence for liquid outer core

drives earths magnetic field

outer core:

• liquid iron-nickle sulfur

• 2,225 km thick

• 10-12 g/cm cubed

Inner core

• solid iron- nickle alloy

• 13 g/cm cubed

solar wind

• continuous stream of charged particles (plasma) — mainly protons and electrons

• constantly flowing outward from the Sun's outer atmosphere (corona) at high speeds

• carries the Sun's magnetic field throughout the solar system

solar wind distorts what

the magentosphere : teardrop shape

Magnetosphere

deflects most of the solar wind, protect from ionising radiation

Earths layers

• Crust

• Mantle

• outer core

• inner core

Lithosphere

• crust and upper mantle

• uppermost 100-150 km of Earth

• rigid

Astenosphere

• upper mantle below the lithosphere

• shallow under oceanic lithosphere

• deeper under continental crust

• flows as a soft solid

Crust

• Oceanic

• continental

Oceanic

• thinner

• high density (floats lower)

• Mafic (ballistic and gabroic) in composition,- less silica

Continental

• thicker (thickest under mountains)

• low density (floats higher )

• felsic (granitic) to intermediate in composition, more silica