Planetary Geosciences & The Universe PDF

# Planetary Geosciences Knowing the unknown... Planetary geology focuses on understanding the properties and processes of solid-surface objects in the Solar System. A relatively new discipline, planetary geology sees the techniques and understanding of geological phenomena on Earth applied to othe...

# Planetary Geosciences Knowing the unknown... Planetary geology focuses on understanding the properties and processes of solid-surface objects in the Solar System. A relatively new discipline, planetary geology sees the techniques and understanding of geological phenomena on Earth applied to other bodies, some of which appear vastly different to our own world. ## What is Planetary Geology? * The Solar System has an abundance of worlds with solid surfaces. * The terrestrial planets, Earth's Moon, and various other bodies are made of rock and other solid materials, which bear signs of their formation and history. * Planetary geology is the way researchers study the cratering, weather, volcanoes, and other processes that shape worlds in the Solar System. # The Universe * The Universe is commonly defined as the totality of everything that exists, including all physical matter and energy, the planets, stars, galaxies, and the contents of intergalactic space. * Born with the Big Bang, the Universe originated as an unimaginably hot, dense point. ## Who came up with the idea? * The idea of Big Bang was first appeared in scientific form in 1931, in a paper by Georges Lemaître, a Belgian cosmologist. * The term "Big Bang" was first used in the late 1940s by the astronomer Fred Hoyle. * Edwin Hubble was really the person who set up the observations studying the cosmic microwave. # Evolution of Universe * When the universe was just $10^{-32}$ of a second or so old *(i.e., a hundredth of a billionth of a trillionth of a trillionth of a second in age)*, it experienced an incredible burst of expansion known as inflation. * In this cosmic inflation, space itself expanded faster than the speed of light. * The size of the Universe doubled at least 90 times, going from subatomic-sized to golf-ball-sized almost instantaneously. # The Beginning of Everything... * After this initial expansion, which lasted a fraction of a second, gravity started to slow the universe down. * One second after the big bang, the universe consisted of an extremely hot *18 billion degrees Fahrenheit or 10 billion degrees Celsius* primordial soup of light and particles. * The cosmos now contained a vast array of fundamental particles such as neutrons, electrons and protons - the raw materials that would become the building blocks for everything that exists today. # Big Bang and Nucleosynthesis * In the following minutes, an era called nucleosynthesis occurred where protons and neutrons collided and produced the earliest elements - hydrogen, helium, and traces of lithium and beryllium. * **Nucleosynthesis:** After the universe cooled slightly, the neutrons fused with protons to make nuclei of deuterium, an isotope of hydrogen. * Deuterium nuclei then combined to make helium. * Further reactions between protons, neutrons, and different isotopes of helium produced lithium. * The hydrogen and helium produced during this phase of the universe eventually created the universe's first massive stars. * After five minutes of Big Bang, most of today's helium had formed, and the universe had expanded and cooled enough that further element formation stopped. * At this point, though, the universe was still too hot for the atomic nuclei of these elements to catch electrons and form complete atoms. # Recombination * About 380,000 years after the big bang, the universe had cooled enough for atomic nuclei to capture electrons, a phase known as the epoch of recombination. This led to two significant changes in the cosmos: * **First:** With most electrons now bound to atoms, there were not enough free electrons left to scatter light, causing the cosmic fog to lift. The universe became transparent, allowing light to travel freely across vast distances for the first time. * **Second:** The creation of these first atoms generated its own light. This glow, still visible today, is known as the cosmic microwave background, the oldest light we can observe in the universe. # Dark Ages * After the cosmic microwave background, the universe became opaque once more at shorter wavelengths due to the absorption by hydrogen atoms. For the following 200 million years, the universe remained in darkness, with no stars to emit light. * During this time, the cosmos was a vast expanse of hydrogen atoms, helium, and small traces of heavier elements. ## First Stars * Gas in the early universe was not evenly distributed; cooler regions were clumpier, containing denser clouds of gas. * As these clouds grew more compact, their centers heated up until they became hot enough for nuclear fusion to occur, giving birth to the first stars. * These stars were 30 to 300 times more massive than our Sun and millions of times brighter. * Over the course of several hundred million years, they gathered together to form the first galaxies. # Reionization * Initially, starlight couldn't travel far because it was scattered by the dense gas surrounding the first stars. * Over time, the ultraviolet (UV) light from these stars ionized the hydrogen atoms in the gas, breaking them down into electrons and protons. * As this reionization continued, starlight was able to travel greater distances, ionizing even more hydrogen atoms. * By the time the universe reached 1 billion years old, stars and galaxies had ionized almost all the gas, making the universe transparent to light as we observe it today.