Age of Earth and Age of the Universe

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


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!


JPL/ NASA Chronicles of Discovery: Innovations IN SPACE, ON EARTH


From: JPL/ NASA Timeline: Chronicles of Discovery


  • Radar used for the first time to observe another planet when signals are bounced off Venus; a follow-up test reveals surface features as the planet rotates.
  • Digital image processing developed for the Mariner and ranger missions leads to many applications in medicine, law enforcement, and other fields.
  • Error-correcting codes designed to avoid dropouts in radio communication with Mariner spacecraft eventually find their way in to cell phones and compact discs.
  • Technology designed to purify “clean rooms” in which spacecraft are built are adapted for hospital operating rooms and other work environments.
  • JPL collaborates with the Department of Energy to develop low-cost solar panels for home energy and other applications.
  • 3-D computer animation techniques developed to model the flight of spacecraft lay the groundwork for computer-animated cartoon movies of the 1990s.
  • JPL debuts an experimental car powered by a hybrid mix of gasoline and electricity – a precursor of commercial models two decades.
  • Infrared technology from the Viking mission to Mars is adapted to create devices that are inserted into the ear to read body temperature.
  • A JPL team works with doctors from the Los Angeles Cedars-Sinai Medical Center to develop a tool for cleaning out clogged arteries without surgery, JPL excimer laser technology is evaluated as an alternative to balloon technology.
  • A JPL instrument called a spectrometer helps archeologist identify minerals on an ancient Guatemalan funeral mask.
  • An imaging system is created for the National Archives to monitor and preserve the original copies of the Constitution, the Declaration of Independence, and the Bill of Rights.
  • Explorers discover the lost city of Ubar, an outpost on the spice route of the Arabian Peninsula, thanks in part to images from radar imagers flown on the space shuttle.
  • Shuttle astronaut John Glenn helps test JPL’s Electronic Nose, a device that measures trace vapors in close environments. Applications include environmental monitoring, quality control, food processing, and medical diagnosis.
  • An ultrasonic drill is developed that adapts easily to extreme temperatures and can core the hardest rocks. The drill has application in space missions and in medicine.
  • JPL establishes a Global Positioning System ground network that provides highly precise location information for use in agriculture, earthquake monitoring, and aviation.
  • JPL’s rugged urban robot, known as “Urbie,” is developed as a prototype for military reconnaissance and police, emergency, and rescue personnel.
  • JPL scientists create a transparent welding curtain technology that maximizes protection from blue and ultra-violet radiation. They follow this with a superior technology for protective sunglasses for various light environments.
  • A tiny image sensor on a chip developed by JPL researchers originally for space imaging application has now become widely available for consumer use, cell phone cameras, digital still and video camera, and personal computer cameras use the image chip, which is easier to manufacture and consumes less power than other images sensors.
  • EPOXI is a multiple-use spacecraft. Originally Deep Impact, EPOXI was renavigated to a different comet, Hartley 2. EPOXI also observed extrasolar planets and tested the “Interplanetary Internet” from deep space.
  • JPL robot technology was used by a U.S. firm to create two mobile robots that investigated damage at Japan’s devastated Fukushima nuclear power station.

JPL/ NASA Chronicles of Discovery: Timeline (1990-2011)

Mars Rovers

From: JPL/ NASA Timeline: Chronicles of Discovery

August 10, 1990: Magellan enters orbit around Venus. Over the next four years, it maps 98 percent of the planet’s surface.

October 6, 1990: The U.S. – European Ulysses spacecraft launches a mission to study the Sun and its poles.

October 29, 1991: En route to Jupiter, Galileo makes the first flyby of an asteroid when it passes by Gaspra.

August 10, 1992: The U.S. – French ocean-monitoring satellite Topex/ Poseidon launches.

August 28, 1993: Galileo flies by a second asteroid, Ida, on its way to Jupiter.

December 2, 1993: Shuttle astronauts take a spacewalk to install JPL’s Wide-Field and Planetary Camera 2 in the Hubble Space telescope, compensating for a flaw in the telescope’s main mirror. The instrument allows Hubble to capture remarkable images of galaxies, nebula, planets, and many other celestial objects.

April 9, 1994: A decade after the first shuttle radar imaging mission, the third in the series launches. A JPL instrument is combined with a German-Italian radar system.

December 7, 1994: Galileo arrives at Jupiter, delivering a descent probe into the giant planet’s swirling atmosphere.

August 17, 1996: The NASA Scatterometer launches aboard Japan’s Advanced Earth Observing Satellite. The instrument studies near-surface ocean winds.

November 7, 1996: Mars Global Surveyor launches on a mission to orbit the red planet.

December 4, 1996: Mars Pathfinder launches, carrying a lander and instrumented rover.

February 12, 1997: JPL teams with a Japanese spacecraft launched under the Space Very Long Baseline Interferometry program to make radio observations of the distant Universe.

July 4, 1997: Mars Pathfinder lands, delivering the first mobile rover to another planet, By the final data transmission on September 27, the mission returns 2.3 billion bits of information, including more than 16,500 lander images and 550 rover images.

September 12, 1997: Mars Global Surveyor enters orbit.

October 15, 1997: Cassini launches to travel 6-1/2 years to Saturn, where the European-built Huygens probe will descend to the surface of the shrouded moon Titan.

February 17, 1998: Voyager 1 passes another spacecraft to become the most distant human-made object in space.

October 24, 1998: Deep Space 1 launches on a mission to flight-test advanced technologies, including an ion propulsion system.

February 7, 1999: Stardust launches on a mission to fly past a comet and return samples of comet and interstellar dust to Earth.

June 19, 1999: The Quick Scatterometer satellite launches into Earth orbit to study near-surface ocean winds around the globe.

December 18, 1999: Two JPL instruments, the Multi-angle Imaging SpectroRadiometer and the Advanced Spacebourne Thermal Emission and Reflection Radiometer, launch aboard NASA’s Terra satellite.

December 20, 1999: The Activity Cavity Irradiance Monitor Satellite launches to study the energy output of the Sun.

February 11, 2000: The Shuttle Radar Topography mission launches. The instrument uses a pair of large antennas to make a near-global map of Earth’s topography.

December 30, 2000: En route to Saturn, Cassini flies by Jupiter, making joint observations of the giant plant with the Galileo spacecraft.

April 7, 2001: Mars Odyssey launches; it enters orbit at the red planet on October 24.

August 8, 2001: Genesis launches on a mission to return samples of the solar wind to Earth.

December 7, 2001: The U.S. – French Jason 1 oceanography satellite launches.

March 17, 2002: Twin Earth-orbiting satellites are launched under the gravity Recovery and Climate Experiment mission.

May 4, 2002: JPL’s Atmospheric Infrared Sounder instrument launches aboard the Aqua satellite to study Earth’s climate and weather.

April 28, 2003: Galaxy Evolution Explorer launches to study the history of star formation.

June 10, 2003: Mars Exploration Rover “Spirit” launches to Mars.

August 25, 2003: Spitzer Space Telescope launches. It uses infrared technology to study asteroids, dust-shrouded stars, and distant galaxies.

January 3, 2004: Mars Exploration Rover “Spirit” lands at Gusev Crater on Mars.

January 24, 2004: Mars Exploration Rover “Opportunity” lands at Meridiani Planum on Mars.

March 2, 2004: JPL’s Microwave Instrument on the Rosetta Orbiter launches.

May, 2004: The Mars Exploration Rover begins the first of several extended missions.

June 30, 2004: Cassini-Huygens enters Saturn’s orbit.

July 15, 2004: JPL’s Microwave Limb Sounder and Tropospheric Emission Spectrometer launch aboard the Aura satellite to study ozone in Earth’s atmosphere.

January 12, 2005: Deep Impact launches to encounter comet Tempel 1.

January 14, 2005: The Huygens probe lands on Titan, Saturn’s mysterious smoggy moon.

July 3, 2005: Deep Impact’s impactor collides with comet Tempel 1.

August 12, 2005: Mars Reconnaissance Orbiter launches to seek out the history of water on the red planet.

July 3, 2007: Deep Impact becomes the EPOXI mission, retargeted to comet Hartley 2.

August 4, 2007: Phoenix, a Mars lander, launches to the red planet.

August 13, 2007: The Stardust spacecraft is reactivated to conduct a follow-up visit to comet Tempel 1.

September 13, 2007: Mars Exploration Rover “Opportunity” descends into Victoria Crater.

September 27, 2007: The Dawn mission to asteroid Vesta and the dwarf planet Ceres launches.

May 25, 2008: Phoenix lands near Mars’ North Pole to dig for water ice and analyze the soil.

June 20, 2008: The Ocean Surface Topography/ Jason 2 mission launches.

June 30, 2008: Cassini begins its first extended mission, called the Saturn Equinox mission.

October 22, 2008: The Moon Mineralogy Mapper launches aboard India’s Chandrayaan-1.

March 6, 2009: The Kepler mission launches on a search for Earth-like planets.

March 14, 2009: JPL technology launches on the European Space Agency’s Herschel/ Planck mission.

June 18, 2009: Diviner launches aboard Lunar Reconnaissance Orbiter to map temperatures at the lunar North Pole.

December 14, 2009: Wide-field Infrared Survey Explorer launches. It will scan the sky in infrared light, creating a vast catalog of celestial objects.

May 20, 2010: The Mars Exploration Rover project passes a historic longevity record: “Opportunity” rover surpasses the duration record set by the Viking 1 lander of 6 years and 116 days operating on the Martian surface.

September 27, 2010: Cassini begins its second extended mission, named the Cassini Solstice Mission.

November 1, 2010: The giant 70-meter (230-foot) antenna at the Goldstone Deep Space Communications goes back on line tracking deep space missions after a seven-month upgrade.

November 4, 2010: Deep Impact-EPOXI flies by comet Hartley 2.

December 25, 2010: Mars Odyssey becomes the longest-serving spacecraft at Mars – 3,340 days in orbit.

June 10, 2011: Aquarius launches to study Earth’s sea-surface salinity.

July 15, 2011: The Dawn Spacecraft enters orbit around asteroid Vesta.

August 5, 2011: Juno launches to Jupiter to explore the origin and evolution of the giant planet.

September 10, 2011: Gravity Recovery and Interior Laboratory twin spacecraft launch to explore the Moon’s gravity.

November 26, 2011: Mars Science Laboratory, “Curiosity” launches. The rover will investigate whether conditions on Mars have been favorable for life.

December 5, 2011: The Kepler Mission announces its first exoplanet in a Sin-like star’s habitable zone.

JPL/ NASA Chronicles of Discovery: Timeline (1950s-1989)

Voyager 1

From: JPL/ NASA Timeline: Chronicles of Discovery

January 31, 1958: Built in just three months, Explorer 1 is launched as the first U.S. satellite; it discovers the Van Allen radiation belts.

March 3, 1959: Pioneer 4 launches and escapes Earth’s gravity to orbit the Sun.

August 27, 1962: Mariner 2 launches and conducts the first flyby of another planet when it visits Venus on December 14.

July 28, 1964: Ranger 7 launches and executes an intentional crash-landing into the Moon on July 31. As it closes in, it sends back more than 4,000 pictures of the lunar surface.

November 28, 1964: Mariner 4 launches with a destination of Mars.

February 17, 1965: Ranger 8 launches and impacts the Moon in Mare Tranquillitatis three days later. This location will become the landing spot for the Apollo 11 astronauts 4-1/2 years later.

March 21, 1965: Ranger 9 launches and three days later impacts the Moon in the 108-kilometer-diameter (67-mile) crater Alphonsus, sending back more than 5,800 images.

July 14, 1965: After an eight-month voyage to Mars, Mariner 4 makes the first flyby of the red planet. The spacecraft radios back the first close-up photos of another planet.

May 30, 1966: Surveyor 1 launches. On June 2, it becomes the first U.S. spacecraft to make a soft landing on the moon.

April 17, 1967: Surveyor 3 launches, lading on the Moon on April 20. Two and a half years later, the Apollo 12 astronauts will land nearby and photograph the Surveyor 3 site.

June 14, 1967: Mariner 5 launches and flies by Venus on October 19.

September 8, 1967: Surveyor 5 launches and lands on the Moon September 11.

November 7, 1967: Surveyor 6 launches and soft-lands on November 10. The lunar mission runs until December 14.

January 7, 1968: Surveyor 7, the last of the Surveyor series, launches and soft-lands on the Moon on November 9. Overall, the Surveyors acquire 90,000 images from five sites on the Moon.

February 24, 1969: Mariner 6 launches. A month later, on March 27, Mariner 7 launches. They complete the first dual mission to Mars with flybys on July 3 and August 5.

May 30, 1971: Mariner 9 launches and reaches Mars on November 13, becoming the first spacecraft to orbit another planet. The craft operates for nearly a year around Mars.

November 3, 1973: Mariner 10 launches on a mission to Mercury and Venus, the first craft designed to visit two planets.

February 5, 1974: Using gravity-assist for the first time, Mariner 10 swings by Venus to borrow the planet’s gravity to propel it on to Mercury, which it passes on March 29. On September 21, it flies past Mercury again.

March 16, 1975: Mariner 19 flies by Mercury a third time.

August 20, 1975: Viking 1 launches an orbiter and lander toward Mars. On September 9, Viking 2 launches a similar orbiter- lander pair.

June 19, 1976: Viking 1 arrives in orbit at Mars. On July 20, its lander becomes the first craft to soft-land on another planet. On August 7, Viking 2 arrives in orbit, and its lander touches down on September 3.

August 20, 1977: Voyager 2 launches, followed by the launch of Voyager 1 on September 5.

June 26, 1978: The experimental Seasat satellite launches to test four instruments that use radar to study Earth and its seas. The satellite collected more ocean topography data than the previous 100 years of shipboard research.

March 5, 1979: Voyager 1 makes its closest approach to Jupiter. On July 9, Voyager 2 flies by the giant planet. Together, the Voyagers take more than 22,000 images of Jupiter and its moons.

November 12, 1980: Voyager 1 flies by Saturn.

August 25, 1981: Voyager 3 flies by Saturn.

October 6, 1981: The Solar Mesosphere Explorer launches to study processes that create and destroy ozone in Earth’s upper atmosphere.

November 12, 1981: The first in a series of radar imagers is launched on the space shuttle.

January 25, 1983: The Infrared Astronomical Satellite launches into Earth orbit. The telescope discovers solid material around distant stars, strongly suggesting the existence of planets.

October 5, 1984: The second in a series of imaging radar missions launches on the space shuttle.

January 24, 1986: Traveling to a planet more distant than any visited before, Voyager 2 makes the first ever flyby of Uranus, nearly 3 billion kilometers (1.8 billion miles) from Earth. Voyager images 15 of Uranus’ moons.

May 4, 1989: Magellan launches a mission to Venus.

August 25, 1989: Voyager 2 is the first spacecraft to fly by Neptune.

October 18, 1989: Galileo launches on a six-year journey to Jupiter.

Meteors, Meteorites, and Meteoroids


Meteors, Meteorites, and Meteoroids

Meteoroids are debris in space from comets or asteroids; meteors are shooting stars or fire balls in air; meteorites are meteoroids that invade Earth’s atmosphere and impact the ground; micrometeorites are perfect shiny spheres microscopic in size and the major cause of small-scale erosion on the moon. The three major types of meteoroids are stony, stony iron, and iron.

  • Several meteors can be seen per hour on any given night; when this number increases dramatically, these events are called “meteor showers” that occur annually or at regular intervals as the Earth passes through the trail of dusty debris left by a comet
  • The Perseids peak around August 12 every year; each Perseid meteor part of the comet Swift-Tuttle that swings around the Sun every 135 years
  • Other meteor showers and their associated comets: Leonids (Tempe-Tuttle), the Aquarids and Orionids (Halley), and the Taurids (Encke)
  • Comet dust in meteor showers burns up in the atmosphere before reaching the ground
  • Most meteorites no bigger than an average Earth rock
  • Large meteorites can cause extensive destruction: Barringer Meteor Crater in Arizona (1,000 meters, 50,000 years old), asteroid impact which created the 300 km Chicxulub crater on Yucatan Peninsula (65 million years ago)
  • Ann Hodges of Sylacauga, Alabama was severely bruised by a 3.6 kilogram stony meteorite that crashed through her roof in November, 1954
  • Meteorites have a “burned” exterior, formed as the meteorite is melted by friction as it passes through the atmosphere
  • Three types of meteorites: “irons,” “stones,” “stony-irons”
  • More than 30,000 meteorites found on Earth, 99.8% came from asteroids
  • Evidence for an asteroid origin includes: orbits calculated from photographic observations of meteorite falls project back to the asteroid belt, spectra of several classes of meteorites match those of some asteroid classes
  • All but rare lunar and Martian meteorites are very old, 4.5-4.6 million years
  • Only one group of meteorites can be traced to a specific asteroid; eucrite, diogenite, and howardite igneous meteorites traced to third largest asteroid Vesta
  • Meteorites and asteroids that fall on Earth are of the original diverse materials from which planets formed; tells the conditions and processes during the formation and earliest history of the solar system
  • Remaining 0.2% of meteorites split equally between meteorites from the Moon and Mars
  • 35 known Martian meteorites blasted off Mars by meteoroid impacts; all igneous rocks crystallized by magma
  • Controversy of whether structures in meteorite ALH84001 might be evidence of fossil Martian bacteria
  • 36 lunar meteorites similar in mineralogy and composition to Apollo Moon rocks, but come from other parts of the Moon


4.55 billion years ago: Formation age of most meteorites, age of the solar system

65 million years ago: Chicxulub impact leads to the extinction of dinosaurs and 75 percent of animals on Earth

50,000 years ago: Age of Barringer Meteor Crater in Arizona

1478 BC: First recorded observation of meteors

1794 AD: Ernst Friedrick Chladni publishes first book on meteorites

1908 (Tunguska), 1947 (Sikote Alin), 1969 (Allende and Muchison), 1976 (Jilin): Important 20th century meteor falls

1969: Discovery of meteorites in a small area of Antarctica leads to annual expeditions by US and Japanese teams

1982-1983: Meteorites from the Moon and Mars are identified in Antarctic collections

1996: A team of NASA scientists suggests that Martian meteorite ALH 84001 may contain evidence of microfossils from Mars

2005: NASA’s Mars Exploration Rover Opportunity finds an iron meteorite on Mars

References: NASA <>

The Solar System: Basics

The Solar System


  • Eccentricity of Orbit: measures the ellipticity of orbit (ranges 0-1, with 0 as spherical and 1 as very elliptical)
  • Density: mass per unit volume; mass in grams and volume in cubic centimeters
  • Oblateness: measures how much the middle section of the planet bulges
  • Surface Gravity: the larger the surface gravity, the thicker the atmosphere as gravity pulls in more gases
  • Albedo: measures the fraction of light reflected compared to the amount of light received from the Sun; the higher the albedo, the more reflective the surface
  • Escape Velocity: minimum speed or velocity needed to escape the planet’s gravitational pull
  • Rotation: most planets rotate in counter-clockwise direction (prograde); others rotate in the clockwise direction (retrograde)
    • Rotational period is shortest for gaseous planets and longest for Venus
  • Roche Limit: about two and a half times the radius of the planet; within the Roche Limit, matter cannot accretes to form moons because the tidal force of the planet tears matter apart to form rings

Giant Planets: Giant planets have lighter elements such as hydrogen and helium in their atmospheres. They have stronger gravity and are at larger distances from the Sun. Jupiter, Saturn, and Neptune are stormy with great spots of lasting storms and belts and zones. However, Uranus is comparatively bland and uniform. All giant planets are home to convection, or hot gases rising and cold gases falling.

Terrestrial Planets: Terrestrial planets have heavier elements such as carbon, oxygen, and nitrogen. Mercury is most heavily cratered while Earth is least cratered. Larger terrestrial planets have plate tectonics. Earth has a sizable magnetic fields that can protect it from solar wind particles and Van Allen Belts. Earth has the “Goldilocks phenomenon,” or the right conditions for the development of life.