Origins and Structure: Earth and It’s Oceans Unit 1: Chapter 2 in Garrison 6th Edition
Humankind appears A Timeline of Earth’s History Fig. 1.12, p. 12
The Milky Way is not just a candy bar… • Our galaxy is called the Milky Way and is composed of stars, dust, gas and other materials held together by gravity. • Stars are composed of incandescent gases. • The sun is a star • Earth was formed by stars
The Life of a Star • Life: An area of spinning nebulae (clouds of gas and dust) begins to shrink and heat up. Protostar forms as it flattens and condenses at the center into a knot of gases Nuclear fusion, hydrogen fuses to form helium, begins at 10 million degrees Celsius = energy • We now have a star, stable and no longer shrinking or expanding. • Source of food = hydrogen fuel • Job = convert H into other elements like O and C • Death begins as it consumes these C and O atoms. • Extreme temperatures can form atoms up to the mass of iron
Collapse of a Star • Without hydrogen the star begins to collapse on itself increasing the internal temperature. • Intense compression causes an extreme expansion = Supernova • The star is blown to bits and the shattered mass expands outward. • Almost the speed of light, 30 seconds beginning to end • Now can from atoms heavier then iron. • Earth was an indirect result of a supernova explosion
The Formation of Earth • The Big Bang – approximately 14 BYA Mass and energy began to expand from a geometric point. Evidence: Galaxies are still moving away from us at a speed proportional to their distance. • Early Universe expanded and began to cool. • Cooling allowed for the formation of atoms, such as hydrogen which is the most abundant form of matter still today.
Solar Nebula: Our Special Event • Thin cloud struck by a supernova causing two important events: 1) Condensing mass began to spin 2) The nebula absorbed heavier atoms passing by. • This now spinning mass became our solar system….inner most portion = sun (protosun) outer material = planets (protoearth)
Formation of the Solar System: Nebular Hypothesis The Sun and planets formed by accretion (smaller particles in the spinning nebular cloud clumping together to form larger objects)
Birth of Planets • Accretion (30 to 50 million years) = clumping of small particles into larger masses. • First to form: Jupiter, Saturn, Uranus, and Neptune Why? Cooler temperatures allowed methane and ammonia ices to congeal together. • Higher temperatures near the protosun allow solidifying of metals and some rock minerals ex) Mercury which is mostly iron. • Earth with an array of elements is somewhere in the middle.
A sun and solar system is born • Our sun begins to fuse hydrogen into helium, and is no longer considered a protosun. • Solar radiation “blows” away excess particles, which is now only seen in the areas surrounding the outer plants.
Earth Accretion and “Iron Catastrophe” Fig. 1.8, p. 8
Most of the water is here We are here
A Changing Earth Early Earth • Homogenous mixture of colder particles • Earth’s surface heated up by impact of asteroids, comets, and other falling debris. • Heat and gravitational compression causes certain elements to accumulate internally and parts of Earth begin to melt. Density Stratification (4.6 bya) • Iron and Nickel internally increased temps = Core • Other elements, silicon, magnesium, aluminum, and oxygen-bound compounds rose to the surface = Crust
A Changing Earth • Cooling • Another planet crashes into Earth causing the metallic core to combine with Earth’s core. • Rocky mantle was ejected to form a ring of debris, which condensed to form our moon. • Initial atmosphere burned up by the sun, this allowed contained gases to form a second atmosphere. • Outgassing = volcanic venting, which included water vapor that later formed clouds.
Formation of the Oceans and Early Atmosphere Volcanic outgassing Recently some researchers have suggested that ice meteorites could have been an important source of water, although this view has been challenged. Figure 2 – 07
Fig. 1.12, p. 12 Oceans = Volcanic Outgassing + Ice-Rich Comets
Formation of the Oceans • Earth still very hot, no collection of water. • Thick clouds would not allow the sun to reach Earth. • Eventually clouds cooled enough to form water droplets..quick water cycle did not stay on Earth. • 20 million years of heavy rains which eventually deposited minerals and began to collect. • Ocean waters and Earth’s crust grew deeper and thicker. • Icy comets and asteroids would later contribute to our oceans as well. • Today the ocean continues to expand..0.1 Cubic km per year.
Changing Atmosphere • Rich in CO2 , N, Water Vapor, with traces of ammonia and methane. • 3.5 BYA mixture begins to change mostly N and O.
The Early Atmosphere:Very Different Than Today’s There was no oxygen (it would be made later by photosynthesis), and there were methane, ammonia, and high amounts of carbon dioxide.
Life begins in the ocean • Carbon compounds initiate life. • These carbon compounds might have come from comets and other materials that crashed into our planet. (Miller –Urey Experiment) • Bodies of living organisms are made up of saline water. • Biosynthesis: Organic Compounds to Living Organism • Early oceans were frozen, trapping life, because of a lack of heat given off by the sun. (Good because elements in the atmosphere would have destroyed these simple organisms)
Cyanobacteria The Origin of Life on Earth • The earliest life forms probably arose in the oceans. • Lightning? Hydrothermal vents? Outer space? • The first fossil life forms are primitive bacteria found in rocks >3.5 billion years old! Animals and plants would evolve much later.
The Future • Speculation: 5 billion year maintained as it is. • The sun (star) will eventually die. • Not big enough for a supernova, but will engulf inner planets and eventually the sun will cool.