ASTR178Other Worlds A/Prof. Orsola De Marco 9850 4241 firstname.lastname@example.org
Announcements • Website of the book. It contains many articles and links: http://bcs.whfreeman.com/universe9e/ Help questions (For this week) • 1-28, page 232, 233. • Most of the questions in this chapter are relevantsince I covered this chapter pretty thoroughly.
The Moon Practical • All instructions have been posted on the website. • Download the instructions and the sky chart. • Go out at least 5 times between 14 August and 27 August ~8-9PM. • Plot the Moon position on the Sky Chart provided, includingthe Moon’s phase. • Always go out at the same time for instance sometime between 8 and 9 pm. IF YOU DO NOT THE EXPERIMENTWILL NOT WORK. • Answer the questions. • Return the work to the boxes by September 17.
In last class • A quick wrap up of the magnetic fields in the Solar System. • Earth’s energy sources • The Greenhouse effect • Earth’s inner layers (we started it, we will finish in this class).
In this class • Earth’s inner layers • Plate tectonics • A few rock definitions • Earth’s early atmosphere and the rise of oxygen • Earth’s current atmosphere, temperature, pressure and circulation. • The Human effect on the atmosphere and climate. • We started talking about the moon, but this will be the subject of Week 4, Class 1.
Richard Dixon Oldham (Irish) 1858-1936 Hypothesized the existence of a molten core. Inge Lehmann (Danish)1888-1993 Hypothesized the existence of the inner core
Alfred Wegener (German) 1880-1930 Plate tectonics Arthur Holmes (British) 1890-1965
Roethosaurus – Early-mid Jurassic From Queensland!
Tectonic activity is cyclic • What we know of the tectonic movement (Pangaea to today) lasted ~200 million years. • Before then another cycle had taken place.The supercontinent before Pangaea was named Rodenia (1100-700 million years ago). • Tectonic activity has a ~500 million year “cycle”. “Pangaea Ultima” a possible next supercontinent http://science.nasa.gov/science-news/science-at-nasa/2000/ast06oct_1/
Types of tectonic activity • Converging – subduction zones (Chile coast) Himalayas • Spreading – mid-Atlantic rift • Sliding – St. Andreas fault
All plate boundaries are sources of volcanism and earthquakes Show Science Bulletins “Earthquakes today”: www.amnh.org/sciencebulletins/
The St. Andreas Fault –a type of conservative plate boundary
A few “rock” terms • Chemical elements make minerals (single atom or compounds) • Single atom: diamond, gold nugget. • Compound: feldspar=K,Al,Si,O; quartz=Si,O) • One or more minerals make rocks • Rock: granite = feldspar + quartz Granite Feldspar Quartz
Plate tectonics and the variety of rocks An example:In the early Earth CO2 was outgassed from volcanos. As it dissolved in the oceans it formed carbonate minerals.One such mineral, calcite becamepart of sedimentary rocks such as limestone, which werelater subducted, mixed up resulting in,e.g., marble is a metamorphic rock.
Earth’s early atmosphere • Early atmosphere: H, He, C, O, …. Same mix as the solar nebula • H, He easily escape, some H forms H2O which remains • Early atmosphere very dense and filled with water vapour • Earth cools, vapour becomes liquid, forms oceans • Earth would be very cold at this point, but CO2 outgassed from volcanoes is a green-house gas and keeps Earth warmer than itwould be otherwise. • CO2 is a green-house gas: in the atmosphere to keep the Earthwarm • Some CO2 dissolves in water and goes in the oceans where it is locked in rocks – some CO2 remains in the atmosphere • When we release too much CO2in the atmosphere we increase the green-house effect and … the end of the story when we talk more about the roasting surface of Venus!
The rise of Oxygen and complex life • Photosynthesis + Respiration: regulation of O2
Life on Earth Humans (~100,000 yr ago) Cambrian explosion (~500 Myr ago) Protoplanetary disk(~4.5 Gyr ago) First life (~3.8 Gyr ago)
The rise of oxygen • Science Bulletin’s piece www.amnh.org/sciencebulletins/
Pressure decreases with altitude. Temperature is more complicated … At hundreds of degrees, why isthe Shuttle notburning up? 50% of the atmosphere is in the troposphere.
The Earth biosphere • Climate can vary by natural causes (uneven Sun’s radiation, Earth’s axisprecession …). • CO2 levels can also vary naturally (intense periods of volcanic activity:extinction 250 million years ago driven by volcanoes in Siberia ….). • However, human influence ha been far above these natural chances (deforestation, destruction of the ozone layer, increase in CO2 emission).
90% of Ozone is between 40 and 60 km above ground. Ozone is O3. It is broken down by UV light so it absorbs UV light and protects us from it. It is then made by a reaction of O2 an O. It is alsodestroyed by reacting with O, a reaction that is catalysed by other chemicalssuch as CFCs
An Inconvenient Truth, by Al Gorehttp://video.google.com/videoplay?docid=2078944470709189270
Observations of the Moon • Aristotle thought that the lunar imperfections wereactually changes in density and the Moon was a perfect orb. • Plutarch (46-120 AD) suggested that it was due to canyons and valleys and might be inhabited. • It was Galileo that finally put the matter to rest using a telescope. • Influence of the Moon on human life.
One small step for (a) man, one giant leap for mankind http://www.youtube.com/watch?v=RMINSD7MmT4 Must watch the great Aussie movies “The Dish”.
Key Ideas • The Earth’s Energy Sources: All activity in the Earth’s atmosphere, oceans, and surface is powered by three sources of energy. • Solar energy is the energy source for the atmosphere. In the greenhouse effect, some of this energy is trapped by infrared absorbing gases in the atmosphere, raising the Earth’s surface temperature. • Tidal forces from the Moon and Sun help to power the motion of the oceans. • The internal heat of the Earth is the energy source for geologic activity.
Key Ideas • The Earth’s Interior: Studies of seismic waves (vibrations produced by earthquakes) show that the Earth has a small, solid inner core surrounded by a liquid outer core. The outer core is surrounded by the dense mantle, which in turn is surrounded by the thin low-density crust. • Seismologists deduce the Earth’s interior structure by studying how longitudinal P waves and transverse S waves travel through the Earth’s interior. • The Earth’s inner and outer cores are composed of almost pure iron with some nickel mixed in. The mantle is composed of iron rich minerals. • Both temperature and pressure steadily increase with depth inside the Earth.
Key Ideas • Plate Tectonics: The Earth’s crust and a small part of its upper mantle form a rigid layer called the lithosphere. The lithosphere is divided into huge plates that move about over the plastic layer called the asthenosphere in the upper mantle. • Plate tectonics, or movement of the plates, is driven by convection within the asthenosphere. Molten material wells up at oceanic rifts, producing seafloor spreading, and is returned to the asthenosphere in subduction zones. As one end of a plate is subducted back into the asthenosphere, it helps to pull the rest of the plate along.
Key Ideas • Plate tectonics is responsible for most of the major features of the Earth’s surface, including mountain ranges, volcanoes, and the shapes of the continents and oceans. • Plate tectonics is involved in the formation of the three major categories of rocks: igneous rocks (cooled from molten material), sedimentary rocks (formed by the action of wind, water, and ice), and metamorphic rocks (altered in the solid state by extreme heat and pressure).
Key Ideas • The Earth’s Magnetic Field and Magnetosphere: Electric currents in the liquid outer core generate a magnetic field. This magnetic field produces a magnetosphere that surrounds the Earth and blocks the solar wind from hitting the atmosphere. • A bow-shaped shock wave, where the supersonic solar wind is abruptly slowed to subsonic speeds, marks the outer boundary of the magnetosphere. • Most of the particles of the solar wind are deflected around the Earth by the magnetosphere. • Some charged particles from the solar wind are trapped in two huge, doughnut-shaped rings called the Van Allen belts. An excess of these particles can initiate an auroral display.
Key Ideas • The Earth’s Atmosphere: The Earth’s atmosphere differs from those of the other terrestrial planets in its chemical composition, circulation pattern, and temperature profile. • The Earth’s atmosphere evolved from being mostly water vapor to being rich in carbon dioxide. A strong greenhouse effect kept the Earth warm enough for water to remain liquid and to permit the evolution of life.
Key Ideas • The appearance of photosynthetic living organisms led to our present atmospheric composition, about four-fifths nitrogen and one-fifth oxygen. • The Earth’s atmosphere is divided into layers called the troposphere, stratosphere, mesosphere, and thermosphere. Ozone molecules in the stratosphere absorb ultraviolet light. • Because of the Earth’s rapid rotation, the circulation in its atmosphere is complex, with three circulation cells in each hemisphere.