Understanding the Universe: From Cosmology to Plate Tectonics

Posted on May 22, 2024 in Geology

Cosmology

• 3,000 years ago, keen observers—the first astronomers (people who study celestial bodies)—realized that what they could see above had a recognizable order: light visible to the naked eye moved slowly across the sky nightly, as if revolving around a fixed point. These points became known as the stars
• Greek philosopher (Homer) (people in the Mediterranean region) considered Earth to be a flat disk with land towards the center and water around the margins, lying at the center of a celestial sphere, a dome to which the stars were attached.
• Philosophers of Homer’s day argued about the nature of the Sun and why it produced heat and light: to some, the Sun was a burning bowl of oil, while to others it was a ball of red-hot iron. Many favored the notion that movements of celestial bodies represented the activities of gods and goddesses, and they named constellations—distinctive arrangements of stars—after these deities. Other societies developed quite different mythologies, full of symbolism, in which to interpret the heavens

Geocentric vs. Heliocentric Concepts

• Geocentric model –> The Earth sits without moving at the center of the universe while the Moon and the planets whirl around it in circular orbits
• The geocentric model is flawed because the stars are fixed in position relative to each other and the stars move across the sky every night, rotating about a fixed position

• But there are a few objects that move relative to the background of the stars

• Heliocentric model –> The Sun lies at the center of the universe, with the Earth and other planets orbiting around it

• Galileo Galilei was found suspect of claiming the Earth was not at the center of the universe      
• He was placed under house arrest

• The heliocentric view of the universe is flawed because the sun is not the center of anything beyond our solar system

Formation of the Universe

• The Big Bang Theory –> Formation of hydrogen and Helium
• Gravity causes the collapse of Hydrogen and Helium gas clouds into the first stars
• When hydrogen and helium supplies get low, there are different paths a star can take, including several that involve the explosion of the star into a “supernova”

• Supernova synthesizes heavier elements 

• Nuclear fusion in stars burns light elements to produce energy and heavier elements up to iron 
• Hydrogen, helium, oxygen, carbon, neon, iron, nitrogen, silicon, magnesium & sulfur are the most abundant in the galaxy

Stars, Galaxies, and the Universe

• Star: immense sphere of incandescent gas, mostly hydrogen and some helium, held together by gravity. Almost all stars are orbited by planets that have coalesced from a nebula of gas and dust
• Galaxy: immense grouping of stars
• Universe: immense grouping of galaxies
• Ultra-Deep Field Image, Hubble Space Telescope was viewing the same tiny patch of the sky for 23 days

Formation of the Solar System

  – Q: Why is the solar system made of planes and moons?     A: Nebular theory of solar system formation    — Planetesimals grow by continuous collisions. The interior heats up and gravity pulls the material into a sphere, forming planets and moons.

Earth’s Composition & Structure

Ice Giants, Gas Giants, and Terrestrial Planets

• Ice Giants: Neptune & Uranus
• Gas Giants: Jupiter & Saturn
• Terrestrial planets: Mercury, Venus, Earth & Mars

Terrestrial Planets in the Habitable Zone

• Planets in a “habitable zone” are at the right temperature to host liquid water at their surface

• Not too hot to boil the water      &     Not too cold that all the water freezes

Drake Equation and Earth’s Composition

• The Drake equation suggests we are probably not the only civilization in the solar system
• 66,000 civilization exist

Internal Layers of Earth

• Crust 
• Mantle
• Outer core = iron, really hot and liquid
• Inner core = iron, really hot and solid
• In the outer core, the temperature is slightly higher than iron’s melting point, which is why the outer core is liquid
• Inner solid core –> increase in temperature and pressure as depth increases
• Outer liquid core –> low viscosity, intense pressure increases towards the inner core, changes the melting point of iron and makes it solid