Chapter 7:
lithosphere
100 km of earth, earths crust and uppermost portion of mantle, solid, strong rocky layer
asthenosphere
100-350 km beneath earths surface, under lithosphere, layer of heat-softened, weak, slow flowing plastic rock it is within here that large scale geological processes such as mountains, volcanoes, earthquake and creation of oceans originate
Recap: What is the planet Theia and what did it do?
It was the mars sized planets that collided into earth, reshaping it and giving it the satellite moon.
What are the most ancient fossils found?
3.5 billion years ago single-celled organisms prokaryotes
Hydrosphere + Biosphere
4.0-4.5 billion years ago earth was hit by comets and asteroids that had water and when they landed the water remained in the atmosphere as water vapour However, when the surface of Earth had cooled, water vapour in the atmosphere started to condense and rain began. When it started raining, the hydrosphere was born. Earth's hydrosphere is largely a closed system. This means that you neither lose nor gain water; we have been recycling the water. This ancient Earth was a hostile enviornment, boiling and high CO2 levels primitive microscopic life eventually appeared on Earth, most probably somewhere in the ocean, because it was sheltered from the hostile atmosphere (the appearance of life marked the origin of the biosphere). Whenever the momentous life-event occurred, the biosphere slowly started to change the atmosphere in ways that made it friendlier for the biosphere to grow ever larger. Indeed, the atmosphere eventually became so friendly that, by several hundred million years ago, it was possible for life to leave the sea, stay continuously in contact with the atmosphere, and spread to the land.
How old is the earth
4.5 billion years
how much of earths surface is covered with water?
71%
What is our atmosphere made up of today
78% NITROGEN, 21% OXYGEN, carbon argon and water
What does earths atmosphere consist of?
78% nitrogen, 21% oxygen and then the other 1% contains traces of many elements and compounds (argon, co2, water, krypton and xenon)
How was carbon dioxide levels adjusted in the atmosphere?
As land forms rose above sea level - primarily as a result of volcanic deposits - weathering (by acidic rain) and erosion proceeded. elements ended up in seawater as a result. Calcium was carried by the slightly acidic 'fresh' water of rivers to the sea. Once in the seas, Ca chemically combined with carbon dioxide and formed grains of calcite (CaCO3) which precipitate and form limestone, or may be consumed, again with carbon dioxide, to form skeletons/shells for marine organisms. Thus CO2 is removed from the ocean water/atmosphere. Volcanic eruptions, tectonic processes and biological processes now maintain a continuous flow of carbon dioxide from the atmosphere to the various organic and inorganic "sinks" and back again. The tiny amount of carbon dioxide in the atmosphere at is extremely important to the maintenance of Earth's surface temperature via the greenhouse effect. The greenhouse effect maintains our temperature (without it, the oceans would freeze and life as we know it would be impossible.)
What earth system responds most sensitively to change?
Atmosphere, its always changing because biosphere is always evolving
Whats the most common rock on earth?
Basalt, and basalt is the dominant rock of the ocean floor
The Rock Magnetic Pattern
During the second world war magnetometers used to find sunked submarines were dragged behind ships well the magnetic patterns detected by the instruments showed a pattern of magnetization of earths crust that proved Wegeners hypothesis THUS when basalt lava spills on the ocean floor the lava will cool and temp will drop below the curie point (the magnetite grains will become magnets having the same polarity as earths magnetic field at location of eruption) this rock with magnetite locked inside will carry a record of earths magnetic field at the moment it cooled below the curie point as long as that rock remains unaffected
Earths Magnetic field
Earth has a strong magnetic field generated by electrical currents in the iron-rich core. Interaction of the liquid metal of the outer core flowing past solid metal of the inner core establishes an electrical current which in turn produces a magnetic field. Of the terrestrial planets, Earth's magnetic field is uniquely strong
Convection and Subduction
Explaining why the plates move, heat transfer. CONVECTION: through the earth's radioactive decay heat is produced and is the driving force of moving material around, the solid mesosphere flows like a liquic allowing convection currents to occur hot material from base of mesospher rises to the surface and replaced by colder material from the top, the surface rides on these circular currents (thus: if a plate is pulled down in the subduction zone it may move downward all the way into the mesosphere)
The hypothesis of Continental drift
LEONARDO DA VINCI recognized that some fossils he had collected were remains of seashells since he received these on a mountain top he understood it must've previously been an ocean floor, he predicted that either the mountains were covered by sea or sea floor uplifted into a mountain, since the fossils weren't found everywhere across the land surface he realized that the sea floor uplifted (making a mountain) CHARLES DARWIN then observed the coastline of Chile has been raised as a result of an earthquake, vertical movement was then accepted Continental drift was introduced by ALFRED WEGENER who examined coastlines of either side of atlantic ocean and found that a number of features like mountains and fossils could be connected across the gap of the ocean, the idea of PANGAEA was proposed (atlantic ocean didnt exist and north and south america were joined with europe and africa)
Whats responsible for most of the erosion and weathering of earths continents
Liquid water and it is a unique process
What was the pattern that proved the pangaea theory
On either side of a central ridge running more or less north-south down the Atlantic, they defined a symmetrical pattern of bands of basalt with 'normal' and 'reversed' magnetic polarity someone collected samples in a line perpendicular to the central ridge and on both sides of it, and age dated the samples, the data showed that the ages plus polarity of bands of rock on one side of the ridge was the exact mirror image of the bands on the other side. Without any doubt at all, they had just determined that the ridge was a center of spreading of plates; this was the process needed by Wegener to prove his hypothesis of many years before.
Dating Rocks (2)
Relative age dating: getting the age by looking at rocks around it Absolute age dating: the actual age of rock
What is the iron catastrophe?
Since iron constitutes 30% of earth composition it tells us it was a significant component of early earth and of the impactors from which the protoplanet grew From the impactor of kinetic energy, the upper 500 km of Earth melted and the hot liquid iron formed the upper layer pooled and sunk under its own great weight the sinking of the iron to the planets core caused it to release more energy and the whole planet to melt! It was a huge catastrophe and happened very quickly Because of this the Earths outer layers formed a liquid core of nearly 100% metal and as earth grew the pressure on the inner core was so great it went from liquid to solid (giving earth a hot central core of solid metal inside an outer core of liquid metal)
How was oxygen absorbed?
So since its believed that prokaryotes dominated earth initially and they are anerobic allergic to oxygen, how did they survive? the ocen floor would spew out a lot of lava contianign iron, and when the iron reached the atmosphere it was absorb the oxygen and oxide by rusting thus the oceans had no free oxygen, the pros would make a lot of oxygen due to their ability of photosynthesis then iron would lay on floor killing organisns and cycle would repeat no oxygen escaped the ocean
How did the biosphere change the atmosphere
The biosphere changed the atmosphere in two ways. ----through the process of photosynthesis, the biosphere added oxygen to the atmosphere. - removal of carbon from the atmosphere to form organic matter and limestone, the biosphere lowered the CO2 content; as a result, the temperature declined.
What elements make up 95% of Earths composition?
The elements iron (Fe) (iron alone accounting for 30%), oxygen (O), magnesium (Mg), silicon (Si) and sulphur (S) account for roughly 95% of Earth's composition
Transform Fault Margins
These are boundaries where two plates slide past each other, with no significant vertical motion Sometimes the faults themselves that make up the margin are called STRIKE-SLIP FAULTS. Example: the series of faults cutting across the western edge of California; the most noteworthy is the San Andreas Fault.
Divergent Margins
These are margins characterized by plates moving apart "spreading centres" Example:under-water volcanoes that mark the centre of the Atlantic Ocean; it's appropriately known as the Mid-Atlantic Ridge.
Convergent Margins
These are the boundaries characterized by plates moving towards each other, the edge of one plate (whichever is more dense) sinks beneath the edge of the second plate. we call this action of one lithosphere plate descending under a second plate SUBDUCTION, and the locations are called SUBDUCTION ZONES. Example: the convergent zone marking the western edge of the whole South American continent.
What is the significance of Theban, Polaris and Vega
They are the 'north pole star' and because of when earth rotates its axis moves like a cone patter - called precession- thus the celestial poles change so in egyptian times the north pole star was thuban today its polaris and in 1200 years it will be vega
Basic Facts of Earth
Third planet from the Sun Fifth largest planet. Densest major body in the solar system The first planet out from the Sun to have any natural satellite. Plane of orbit (called the ecliptic) is only 7 degrees from the Sun's equatorial plane Orbital path is very nearly circular. The tilt of the rotational axis (called the angle of obliquity, or the tilt angle) is primarily responsible for seasons.
What are the most common radioactive elements
Uranium and Thorium, because it takes many million-billin of years for the parent to decay (thus there daughters, lead helps date the oldest rocks)
How is CO2 removed from our atmosphere?
Water dissolves CO2 and brings it out of the atmosphere into the ocean through rain.
What is carbon dioxides role in the atmosphere
Water dissolves carbon dioxide, vastly lessening the amount of such gas in the air, and thus the atmospheric pressure. Since carbon dioxide is a very efficient greenhouse gas, it traps the heat of the planet without letting it escape into space. The almost complete removal of carbon dioxide from Earth's atmosphere meant that the temperature on our planet remained at much lower levels than on Venus, and made it possible for life to evolve.
Geological time scale
arranged sequences can be matched with others around the world to be dated These can be then recognized as block PROTEROZOIC (meaning development of life) 545 million yrs ago, Most life during that time was soft-bodied, and constructed of simple cells, ie no fossils PHANEROZOIC the time of the Cambrian Period until present day, abundant complex life present, this is then divided into 3 main peroid -PALEOZOIC (early life) -MESOZOIC (middle life) -CENOZOIC (recent life) *however, at 65.5 million years ago and 251 million years ago some catastrophic event killed off a large portion of life on earth.
mesosphere
below asthenosphere, pressure is so great that the rock is solid but temp is high that material acts like stiff plastic
Core
below the mesosphere is the core divided into liquid outer core and solid inner core, both pure metal (iron) inner core- 5000 and 7000 C (making it hotter than the suns surface)
From surface to core...
both pressure and temp increase, and density increases
anaerobic environment
containing no free oxygen, therefore must get energy from fermentation (breaking down carbs)
Curie point
curie point is a temperature where atoms are very active (but below that temperature, much less so), thus the iron oxide that forms magnetite responds to the magnetic field below its curie point THUS when basalt lava spills on the ocean floor the lava will cool and temp will drop below the curie point (the magnetite grains will become magnets having the same polarity as earths magnetic field at location of eruption) this rock with magnetite locked inside will carry a record of earths magneic field
Volcanic eruptions occur along which plate margins? Earthquakes occur along which plate margins?
divergent and convergent any of three types
Earths Magnetic Field
earth can be thought of as a 2 pole magnet the magnetic field line radiate b/w earths north and south poles a dynamo converts physical energy to electrical energy and anywhere that energy flows, theres a magnetic field surrounding it and sometimes it can go out of whack THUS throughout histroy earths magnetic poles have sometimes been normal and other times opposite (reverse) therefore the poles are always moving, proof that the internal dynamo is always changing
Plate Margins
explains how movement of plates on a sphere doesn't increase or decrease in volume: the boundaries are either pulled apart, pushed together or slides past one another divergent, convergent, transform
Relative Age dating
geologists can unravel the sequence of rock formations by looking at their relative rltshps So, for example, if you found a rock sequence containing a very particular shell or assembly of shells in one location, and studies from another location showed exactly the same rock sequence and assembly of shells, you could say they were the same age. Eventually you'd find that these rocks were younger than some second set of rocks but older than a third set In time, Earth scientists compared rock sections from all over the world and put them into a world-wide time scale.
Recap: What is accretion
growth by accumulation of smaller bodies, dust and gas
What are the zones of differentiation of the earth?
inner core, outer core, mantle and crust, with oceans and atmosphere on top completed by 4.4 billion years ago
Earths Atmosphere
it is unique The atmospheres composition, the atmospheric pressure and its density is the reasons why we have water and life Has changed from original helium and hydrogen atmosphere when earths surface solidified 4.5 billion years ago to an atmpsphere alike our neighbours Venus and Mars - 96% carbon dioxide -2-3% nitrogen -1% other elements TODAY nitrogen dominates at 78% of the atmosphere with oxygen at 21% and the rest carbon, argon and water Our atmosphere exists because water dissolves carbon dioxide and we have a lesson atmospheric pressure
Why is it so hard to date the earth's surface?
its always changing, its an active planet thats always reworking its surface and also the ocean floors have changed because of plate tectonics
How does sea floor spreading occur?
magma from the asthenosphere, erupts along the ocean floor rift, fresh lava spreads down both sides of rift and new basalt rock is formed in bands on both sides (they carry evidence of earths magnetic pole orientation within them)
Absolute Age Dates
minerals are natural clocks because of radiactivity (its unstabe and decays) To determine age: HALF-LIFE- the rate of radioactive decay PARENT- amount of isotop that is in the process of breaking down DAUGHTER- the amount of the isotope produced by the breakdown
Seismic Tomography
plates that are pulled under due to subduction in subduction zones then travel through the atehnsosphere down to the mesosphere and the are cooler than everything else in the mesosphere so we can detect them because they are cooler S waves pass trhough them at a different rate than through hotter mantle
Eukaryotes
right after the oxygen absorption most of iron was consumed and oxygen could exist the ocean, eukaryotes formed -They used oxygen for respiration, -Grew rapidly in very large colonies, -Were truly photosynthetic (so produced large amounts of oxygen), -Thus contributed a great amount of oxygen to the atmosphere, and rapidly changed the biosphere of Earth
Biosphere
the atmosphere esentially nurtures the biosphere
Mantle Plumes
the boundary between core and mesosphere is quite messy with numerous irregular protuberances into the mesosphere Mesosphere, the zone of stiff plastic, is not stable next to liquid metal core, thus the heat of the core produces large pockets of hot and less dense material that rises like a hot balloon through the more stable mesosphere even travelling all the way to the base of the lithosphere once it reaches lithosphere it breaks through the layer immediately forming volcanoes, OR it pools under lithosphere gradually pushing upwards until it urupts into a volcanoe.
What are the three main things that make Earth different from other planets?
the composition of our atmosphere liquid water on surface (hydrosphere) our biosphere
Plate tectonics
the earths lithosphere is divided into plates and they are always moving because of the moving plastic beneath it (mantle) other terrestrial planets have similar structures to earth but not same tectonics the moving of these plates dictate most of the things around us (like our minerals and rocks and our atmonsphere and hydrosphere)
What is differentiation
the idea that at the core the heaviest elements remain and closer to the surface the lighter elements are there Zonation of elements positions elements from heaviest at the core to lightest at the top, but zonation was not complete so there are still many heavy elements at the surface
Plate tectonics
the primary active process that controls things like volcanism and earthquakes lithosphere asthenosphere 100 km mesosphere 360 km outer core 2.890km inner core 5.150km
Paleomagnetism
the study of magnetic properties of rocks (proved pangaea theory)
what was the beginning of todays atmosphere?
volcanic gases, spewing gas, lava and water vapour and CO2
How do you date something thats organic?
you could use an isotope of carbon thats radioactive (only works for things no older than 100,000 years old)