Origin of solar system

1. Origin of solar system • “Big Bang’ theory • Broadly accepted theory for the origin and evolution of our universe • Postulates that the observable universe started from an instantaneously expanding point 13 to 14 billion years ago • Since then, the universe has continued to expand • Prior to Big Bang, all matter and energy were compacted into single, inconceivably small dense point

2. Evidence for Expanding Universe • Astronomers looking at distant galaxies directly observe this expansion • Originally detected by Edwin Hubble • The expansion of the universe "stretches" light rays converting blue light into red light and red light into infrared light • Example of a Doppler effect • Thus, distant galaxies, which are rapidly moving away from us appear redder • Geologists look to the formation of the solar system to understand formation of the Earth

3. Evidence for “Big Bang” • Expansion of the Universe • Abundance of helium, deuterium and lithium • Thought to be synthesized primarily in the first three minutes of the universe • Thermal spectrum of cosmic microwave background radiation • The universe is filled with the remnant heat from the Big Bang called the "cosmic microwave background radiation“ • Today, this radiation is very cold: only 2.728 degrees above absolute zero. It fills the universe and can be seen almost everywhere we look • Cosmic microwave background radiation appears hotter in distant clouds of gas • Since light travels at a finite speed, we see these distant clouds at an early time in the history of the universe, when it was denser and thus hotter

4. What “Big Bang” does not Explain • Origin of galaxies and the observed large-scale clustering of galaxies • Astronomers observe considerable structure in the universe, from stars to galaxies to clusters and superclusters of galaxies • "Deep Field Image" taken by the Hubble Space Telescope, provides a view of such structure • How did these structures form? • Most astrophysicists believe that the galaxies that we observe today grew gravitationally out of small fluctuations in the nearly-uniform density of the early universe • These fluctuations leave an imprint in the cosmic microwave background radiation in the form of temperature fluctuations from point to point across the sky • Origin of the uniform distribution of matter on very large scales

5. Origin of solar system Pick a theory, any theory, but it must be consistent with these facts: • Planets all revolve around the Sun in the same direction in nearly circular orbits • Counterclockwise direction • The angle between the axis of rotation and the plane of orbit is small (except Uranus) • Roughly perpendicular to the plane of orbit

6. Origin of solar system Pick a theory, any theory, but it must be consistent with these facts: • All planets (except Venus and Uranus) rotate in the same direction as their revolution; their moons do, too • Counterclockwise direction • Each planet is roughly twice as far as the next inner planet is from the Sun

7. Origin of solar system • 99.9 % of mass is in the Sun; 99 % of angular momentum is in the planets • Sun rotates very slowly • Planets in two groups with different chemical and physical properties: • terrestrial (inner): Mercury, Venus, Earth, Mars Mercury is mostly Fe ( = 5.4) • Jovian (outer): Jupiter, Saturn, Uranus, Neptune. Jupiter mostly gas and ice (  = 0.7) Pluto ????

8. Origin of solar system • Terrestrial planets are mostly O, Si, Fe, Mg. The Sun is almost entirely H & He (also important in Jovian planets) • Interplanetary material • Existence of asteroid belt between terrestrial and Jovian planets • Existence of planetary dust

9. Nebular hypothesis • Primeval nebula (slowly rotating cloud of He and H gases + dust) • Initially cloud are stable and move slowly • Occasionally they are disrupted by shock waves from exploding star called a Supernova

10. Nebular hypothesis • Massive explosions create turbulence in the dust cloud induce gravitational instabilities • Gas cloud contracts under the force of gravity and flattens • As a result the cloud starts to rotate in order to conserve its original angular momentum

11. Nebular hypothesis • Eventually, the increasing speed of rotation causes the cloud to collapse into a flat disk

12. Nebular hypothesis • Sun forms and dust particles collide and clump together to form planetesimals

13. Nebularhypothesis

14. Our Solar System

15. Evidence for the Nebular Hypothesis • Because of the original angular momentum and subsequent evolution of the collapsing nebula, this hypothesis provides a natural explanation for some basic facts about the Solar System: • The orbits of the planets lie nearly in a plane with the sun at the center (neglecting the slight eccentricity of the planetary orbit) • The planets all revolve in the same direction • The planets mostly rotate in the same direction with rotation axes nearly perpendicular to the orbital plane • The nebular hypothesis explains many of the basic features of the Solar System, but we still do not understand fully how all the details are accounted for by this hypothesis

16. Collision hypothesis • Portions of the Sun were torn off by a passing star: planetesimals then collided to form planets. • Problems: gases coming from Sun would be too hot to condensestellar collision exceedingly rare.

17. Protoplanet hypothesis • Large gas cloud begins to condense. • Most mass in center, turbulence in outer parts. • Turbulent eddies collect matter meter across; small chunks grow and collide, eventually becoming large aggregates of gas and solid chunks. • Protoplanets, much bigger than present planets, eventually contracted due to their own gravity.

19. The Moon • Only a little smaller than Mercury (small planet in two-planet system). • Surface of the moon very different from the surface of Earth. • No atmosphere, therefore, no weathering.

20. Formation of the Moon • Mars-sized body collides with Earth ~4.5 Billion yr BP • Debris ejected to form Moon

21. A catastrophic impact between theproto-Earth and a Mars-sized impactor

23. Timeline for the Sun, Earth, and Moon

24. Why worry about the beginning? • The evolutionary course is significantly influenced by the initial state. • We know the state of the Earth today relatively well; knowing the beginning will help constrain the in between.

25. A Differentiating Planet

26. Heating of Planet • Accretion. Impacting bodies bombard the Earth and convert their energy of motion into heat • Gravity. As the Earth gets bigger, the extra gravity forces the mass to contract into a smaller volume, producing heat • Just like a bicycle pump gets hot on compression • Radioactive Disintegration. The surrounding material absorbs the energy released in radioactivity, heating up • This is a very slow but steady source of heat • About 20 calories of heat are generated by 1 cubic centimeter of granite in the course of a million years • It would take this amount of rock 500 million years to brew a cup of coffee!

27. An Early Homogeneous Earth Early Earth was a homogenous body

28. Differentiation • Rock is a very poor conductor of heat • So heat continued to build up until some materials started to melt • Calculations have been carried out to determine what happened to the early "homogenous" earth before differentiation • At some point, probably during the first few hundred million years of Earth history a region at a depth of ~500 km became so hot that iron (a plentiful element) started to melt • The molten iron collected and began to sink under its own weight. • About one third of the primitive planet's material sank to the center and in the upheaval heating rates increased and a large part of the body was liquefied

29. Differentiation Begins Irons sinks to the interior and lighter material floats upward

30. Differentiation • The formation of a molten iron core was the first stage of the differentiation • Converted Earth from a homogenous body with roughly the same kind of material at all depths to a zoned, or layered body with a dense iron core, a crust composed of lighter materials with lower melting points and between them the mantle • The first stage of differentiation iron melting (which took a long time to occur) led to the onset of a mechanism that speeded up the differentiation • Convective overturn -- a process whereby molten material may overturn, transferring heat buried deeply within the planet to the outer layers

31. Present day Earth Now Earth is a zoned planet with a dense core and lighter crust

32. Differentiation • Perhaps the most significant event in the history of the Earth • It led to the formation of a crust and eventually the continents • Differentiation probably initiated the escape of gases from the interior • eventually led to the formation of the atmosphere and oceans

33. Origins of the Atmosphere • Some geologists believer that most of the air and water on Earth came from volatile-rich matter of the outer solar system that impacted Earth as it formed • Countless comets may have bombarded Earth bringing water and gas that gave us our oceans and atmosphere • The very hot young Earth would also have lots of volcanic activity leading to outgassing of volatile gases from within the magma • Originally water and gases were locked up in minerals • There is evidence that the hot outgassing that occurred during the first billion years also led to the first atmosphere of the Earth

34. Interacting Earth SystemsVolcanoes contribute gases to the atmosphere and solids to the crust

35. Atmospheric Gases • Did not inherit all our atmosphere from ancestral bodies • Water vapor and other gasses released from rocks by outgassing • Outgassing by volcanic emission occurs today • Water vapor, H, HCl, CO, CO2, N2 • Early atmosphere higher H content • Possibly also ammonia and methane • Gasses from modern volcanoes from recycled rocks • Reasonably sure early atmosphere not from accretion • i.e., accumulation of light volatiles from nebula • Relative scarcity of inert gasses in modern atmosphere • Ar, Ne, Krypton • Too heavy to escape from earths gravity • Less abundant than in atmosphere of stars • Our atmosphere not residue of gasses from nebula

36. Rapid Degassing • Rapid degassing must have produced much water vapor • Condense to form seas when earth cooled sufficiently • Know oceans formed early • Water laid sediments • Metamorphosed sediments date 3.8 by • Detrital grains 4.4 by

37. “Big Burp” • If the Big Bang led to all the universe • The "Big Burp" of differentiation led to much of the environment we live in • It could have occurred over millions of years or it could have been a more catastrophic event • The earliest Earth was probably an unsorted conglomeration • Mostly silicon compounds, iron and magnesium oxides and smaller amounts of all the natural elements

38. Relative Abundance of Elements

39. Earth System Science • Earth should be studied as a unified system • Interactions and interrelationships between all Earth systems • Earth can be divided into 4 subsystems • Biosphere • Lithosphere • Hydrosphere • Atmosphere • Materials and energy cycle among these these subsystems

40. Lithosphere, Hydrosphere, Atmosphere, Biosphere and Uniformitarianism

41. Interacting Earth Systems

42. Kinds of Systems

43. Example of an Open System

44. Another view of the hydrologic cycle

45. The Earth is a Closed System

46. CO2 and Long-Term Climate • What has moderated Earth surface temperature over the last 4.55 by so that • All surface vegetation did not spontaneously catch on fire and all lakes and oceans vaporize? • All lakes and ocean did not freeze solid?

47. Greenhouse Worlds • Why is Venus so much hotter than Earth? • Although solar radiation 2x Earth, most is reflected but 96% of back radiation absorbed

48. Energy Budget • Earth’s temperature constant ~15C • Energy loss must = incoming energy • Earth is constantly receiving heat from Sun, therefore must lose equal amount of heat back to space • Heat loss called back radiation • Wavelengths in the infrared (long-wave radiation) • Earth is a radiator of heat • If T > 1K, radiator of heat

49. Energy Budget • Average Earth’s surface temperature ~15C • Reasonable assumption • Surface of Earth radiates heat with an average temperature of 15C • However, satellite data indicate Earth radiating heat average temperature ~-16C • Why the discrepancy? • What accounts for the 31C heating?

50. Energy Budget • Greenhouse gases absorb 95% of the long-wave, back radiation emitted from Earth’s surface • Trapped radiation reradiated down to Earth’s surface • Accounts for the 31C heating • Satellites don’t detect radiation • Muffling effect from greenhouse gases • Heat radiated back to space from elevation of about 5 km (top of clouds) average 240 W m-2 • Keeps Earth’s temperature in balance