Age of Earth and Age of the Universe

How do scientists determine the ages of the Earth and the Universe? –Peyami

Earth

Age of Earth

Planet Earth is approximately 4.54 billion years old. But how did scientists determine this? With the radiometric dating of meteorites and the ages of the oldest known minerals. While the oldest meteorites found on Earth are approximately 4.5 billion years old, the oldest known mineral, zircon, discovered by Jack Hills in Australia is at least 4.4 billion years old. One meteorite used was the Canyon Diablo meteorite (4.55 billion years old) aged by C. C. Patterson. Since most of Earth’s minerals have undergone change in the core, mantle, and crust by plate tectonics, weathering, and hydrothermal circulation (circulation of hot water), scientists usually cannot use them in dating Earth. However, scientists used ancient Archaean lead ores of galena (natural mineral form of lead II sulfide), the earliest formed homogenous lead isotope, which very precisely dated Earth at 4.54 billion years. Furthermore, inclusions rich in calcium and aluminum in meteorites were formed within the solar system about 4.567 billion years age. As the oldest known solid component of meteorites, these Ca-Al inclusions determine the age of the solar system and set the upper limit of the age of Earth. Scientists do not known the time of Earth’s accretion (growth by gravitationally attracting more matter), but believe it started some after the Ca-Al inclusions formed.

In fact, scientists have long debated over and calculated the age of Earth. People had estimated Earth at just hundred of thousands of years! Later, scientists extended their estimates with more evidence. However, it wasn’t until Charles Darwin, who proposed the theory of natural evolution, that scientists began to make closer estimates. Using the molecular clock and the rate of genetic divergence, scientists estimate the last universal ancestor of all organisms at 3.5-3.8 billion years old.

Expansion of the Universe

Age of the Universe

The age of the Universe is 13.75 billion years old. People long thought the Universe as much younger— millions, let alone billion of years old. Edwin Hubble’s observations in the 1920s showed that the Universe has a finite age. Using Doppler Shift, Hubble discovered that the Universe was expanding. Every galaxy seemed to be moving away from each other, showing red shifts in their spectral lines. In 1958, Allan Sandage made the first calculation of a value called the Hubble’s constant, which determines the rate of the Universe’s expansion. With the Hubble’s constant, Sandage made the first accurate (closer than before) estimate of the age of the Universe at ~20 billion years. Discovered in 1965, the microwave cosmic background radiation, a remnant of the Big Bang, confirmed the expanding Universe theory. As the Universe expanded, it gradually cooled. The CBR shows the Universe at 2.7 K. In fact, scientists have recently discovered dark energy. Dark energy accelerates the expansion of the Universe, reducing earlier estimates of >14 billion years to 13.75 billion years.

Graph of Expansion: Expansion is Accelerating!

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Dark Matter

Dark Matter: Visualization

In 1932, Jan Oort predicted dark matter to account for differences between mass calculated from astronomical objects’ gravitational effects and mass calculated from “luminous” matter contained in these objects (gas, stars, dust). In 1933, Fritz Zwicky observed that galaxies are moving too fast. In the Coma cluster, the gas is moving very fast, held at high temperatures. There must be a lot of gravity unseen to account for the pressure.

From 1965-1985, Vera Rubin discovered: 1. Rotation Curves – stars at the center and the edges travel at the same speeds, the closer the stars, the faster stars should travel, but evidence refuted this; 2. Gravitational Lensing – light is bent from the source as it travels to the observer.

Dark matter is believed to be a new class of subatomic particles. It cannot be seen or detected directly. Since it does not emit or absorb light and other electromagnetic waves, dark matter can only be predicted from its effects on visible matter. Astronomers believe dark matter account for 84% of matter and 23% of mass-energy in the Universe. Like “halos within halos,” dark matter surrounds galaxies, explaining such phenomena observed.

The Big Bang Theory

The Big Bang Theory

About 14 billion years ago, the Universe was much smaller and hotter. In the 1960s, Robert Dicke predicted a remnant “glow” from the Big Bang. In 1965, radio astronomers Penzias and Wilson discovered that glow, named the cosmic microwave background radiation. The CBR was seen in all directions in empty space, with a black body curve (temperature ~3K). About 1 second after the Big Bang, the Universe was very hot, at ~1 billion K. At 3 minutes, protons and neutrons combine to form the nuclei of atoms. The hydrogen/ helium ratio (3:1) found today is about the same as what’s expected after the Big Bang. Atoms were “ionized” with electrons roaming free without being bound. At 300,000 years after the Big Bang, the Universe becomes transparent with a temperature of 3,000K. Light red-shifted by a factor of 1000.

Big Bang: Timeline

*Recent measurements show the Big Bang at 13.75 billion years ago. Scientists recently discovered dark energy; the Universe is not only expanding, but accelerating in expansion. So, earlier estimates of the age of the Universe at 15 billion years have been reduced to 13.75 billion years.

The Universe: Main Points

  1. Expansion of the Universe
  2. Cosmic Microwave Background
  3. Primordial Nucleosynthesis
  4. Evolution of Galaxies and Large Scale Structure Over 14 Billion Years

The Universe: Composition

  • 0.03% heavy elements
  • 0.3% neutrinos
  • 4% stars and gas
  • 25% dark matter
  • 70% dark energy

Expansion of the Universe

Expansion of the Universe

Hubble’s Law, written by Edwin Hubble in the 1920s, describes the expansion of the Universe.

Edwin Hubble & Expansion of the Universe – Timeline

1917: Vesto Slipher discovered that the spectra of galaxies were almost always red shift (moving away). Infact, most galaxies are moving away and 2 out of 15 spirals moving at over 2 million miles per hour.

1929: Edwin Hubble derived distances to these galaxies and showed that implied recessional speed, v1, is proportional to its current distance from us

  • Hubble’s Law: V – H0d, where  H0 is Hubble’s constant (71 km·s –¹/Mpc), v is velocity, and d is distance
  • The value of Hubble’s constant is how fast the Universe is expanding now; if Hubble’s constant is bigger, the Universe is expanding faster

1927: Belgian astronomer, G. Lamaitre, had a similar result, proving that the Universe is expanding

  •  Combined Einstein’s theory of relativity with the redshifts of spiral galaxies
  • Published a paper on mathematical  super structure connecting redshifts and expanding Universe of general relativity, but nobody noticed since he was only an obscure Belgian priest and mathematician
  • Universe began as a single pinpoint, a primordial soup

1998: Acceleration of the expansion of the Universe is caused by “cosmic anti-gravity” or “dark energy” (still unexplained)

Measuring Velocities of Red Shift

  • Light of a galaxy moving away from us will be “red-shifted,” or the wavelength gets longer
  • Light of a galaxy moving toward us will be “blue-shifted,” or the wavelength gets shorter
  • The faster the speed galaxies travel, the more the “red-shift”
  • Objects at the edges of galaxies tend to move faster than objects in the centers

Understanding the Expansion

  • Galaxies are all moving away from us: Does that mean we are at the center of the Universe?
    • No. There is “no” center. All points in space claim to be the center
    • e.g. Raisin bread rising: raising don’t expand, the space between them expands

Olbers’ Paradox— Why is the night sky dark?

  • In the 19th century, astronomer Wilhelm Olbers asked: If the Universe is finite, why isn’t the sky bright from starlight?
  • The solution is not that stars are increasing far away, but that the apparent brightness of a star decreases (1/d²), the area of shells of stars surrounding the Earth increases like d², so the effects cancel out
  • Another solution was that the Universe has finite size, so that not all of the light from all the stars has had time to reach us (Universe expanding); the Universe is 14 billion years old, and we only see “out” 14 billion light years distance from us

Messier: The “M” in M31

What does the “M” in M31 or M11 stand for? Messier [Me-Si-Eh]

Charles Messier

Charles Messier (1758-1772), a French astronomer, identified about 110 diffuse fuzzy objects that he named “Messier objects.” Messier then cataloged these objects in his Messier Catalog. He also discovered 13 comets; finding comets was a way to make a name astronomers of the 18th century).

Messier Catalog

Orion Nebula

M42: Orion Nebula

  • local region in the Milky Way (~1,300 light years away) with new stars
  • appears mostly red due to hydrogen gas abundance

M82: galaxy

  • ~12 million light years away
  • clouds of glowing hydrogen blown out, released by recent star formation

M31: Andromeda Galaxy

Nebulae

  • hundreds of nebulae (discovered 20th century)
  • with George E. Hale’s idea and Hooker’s money –> the Hooker Telescope (100-inch in diameter, 11 years to build, $100 million)

Today, the Sloan Digital Sky Map holds 15 Terabytes of data on the Universe.

The Milky Way – Timeline

The Milky Way Galaxy

HISTORY

1750: Immanuel Kant: advocated the “lens-shaped” distribution of stars, or an “island universe” with galaxies like the Milky Way

1785: William Herschel + Caroline (wife): made the first attempt to determine the shape of the galaxy; found few stars near the edge  and many stars toward the center; determined the galaxy to be an irregular “grindstone” or hockey puck

1900: If the Sun is at the center of the Universe, why is it not brighter at the center? Gas and gas prevent seeing far toward the center and light absorbed and refracted by Earth’s atmosphere  only allows us to see a small portion of the galaxy

Harlow Shapley and Herbert Curtis

1920: The Curtis- Shapley Debate

Harlow Shapley: rising star and “golden boy” of astronomy

  • Since globular clusters are not uniformly distributed uniformly around the Sun, the center of the Milky Way must be centered 30,000 light years away
  • Concluded that the Milky Way is much larger than previously believed (>100,000 light years in diameter)
  • The “nebulae” seen are not island universes but contained in the Milky Way

Herbert Curtis: established astronomer and respected

  • Spiral nebulae are galaxies out side the Milky Way, with high recessional velocities
  • Predicted that these spiral nebulae are the right size to be galaxies –> “huge” galaxy idea

While Shapley advanced that the Sun is not at the center of the galaxy and the galaxy is much larger than believed, Curtis argued that since spiral galaxies are external, there must be more big galaxies.

Who was right? BOTH. Who was wrong? BOTH.

Shapley was right the Sun is not at the center of the Universe. Curtis was right the Universe is composed of many galaxies. However, the size of the Milky Way was in-between their estimates.

1920s-1930s: Edwin Hubble: With the Hooker Telescope on Mt. Wilson, Hubble observed Cepheid Variable stars in the Andromeda Galaxy (M31); Cepheid Variable stars are 500-10,000 brighter than the Sun (in absolute magnitudes)

  • 1920s: Discovered that M31’s distance is too large to be within the Milky Way; M31 is a galaxy like the Milky Way
  • 1930s: Further understanding of the distances and distribution of globular clusters; the scientific community accepted that they underestimated the size of the Milky Way and the Sun is not at its center