The Evolution of Our Understanding: From Earth's Age to the Earth-Moon System

The Evolution of Our Understanding: From Earth's Age to the Earth-Moon System

Our perception of the Earth-Moon system has evolved through the centuries, from ancient fossils to modern radiometric dating methods. This article explores the development of our understanding of the Earth's age and the formation and current state of the Earth-Moon system.

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1. The Earth Moon System Formation, Development, and Current State

2. We were wrong It was once believed that Earth was created, instantly, 6000 years ago. Ancient thinkers like Aristotle and Leonardo da Vinci saw fossils as evidence the Earth was much older. Lord Kelvin used heat to determine an age of 24- 400 million years old Arthur Holmes was the first to get a near accurate age of the Earth using, determining the earth to be about 1.6byo using radioactive decay. Later, improved methods of radiometric dating led to a much more accurate age of the Earth.

3. Formation About 4.5 billion years ago, Earth, along with the other planets in our solar system began to take shape. They formed in accretion disks. The material that formed the Earth was created in supernovas.

4. Proto-Earth Within 10-20 million years Earth, slightly smaller than today, had formed from the accretion disk located about 150,000,000km from the sun. It is hypothesized that another, even smaller planet was also forming at about the same distance. This planet, Theia, was about the size of Mars.

5. Giant Impact Hypothesis Shortly after the formation of these two planets, Theia struck Earth with a glancing blow. This impact liquefied Earth and ejected a large amount of molten material. The ejected material formed the Moon. The remainder of Theia sunk to the center of Earth to help form its iron core. /d1/Big_Slash.gif There are some other, less likely ideas as to how the Moon formed

7. Co-Formation Hypothesis Before, we visited the Moon and were able to analyze its contents, it was thought that the Moon formed at the same time and location as Earth. This would have left the Moon rotating directly above the equator with much more Iron than it currently has.

8. Fission Hypothesis It was also once believed that centrifugal forces pulled a chunk of earth out into space leaving a basin behind which later formed the Pacific Ocean. This would have required the Earth to be spinning much faster than it does today. It also would have formed the Moon rotating directly above the Equator. These facts make this an unlikely hypothesis.

9. Capture Hypothesis Because the Moons orbit is not directly above the equator, it was once believed that the moon was formed elsewhere in the Solar System and later captured by Earths gravity. For this to have occurred the Earth would have needed a much larger atmosphere to slow down the approaching Moon. This too is very unlikely.

10. Explanation The Giant impact Hypothesis is the most likely because it helps explain other features about the Earth Moon system. Large amount of Iron in the core Still molten mantle Tilt of the Earth Speed of Rotation of Earth

11. A Changing Planet Time Line 4.5 bya - Magma Earth 4.4bya - Ocean Earth Carbon dioxide atmosphere, iron rich oceans 3.4bya - Continents form Granite floats on magma 2.2-1.5bya - Blue Planet Stromatolites release oxygen that turns oceans and sky blue.

12. Time Line (cont) 1.0bya Rodinia Super-continent Trilobites best evidence 700mya Snowball Earth Caused by massive super-continent 630mya Cambrian Explosion Shallow seas allows for evolution of a wide variety of life Evidence found in Burgess Shale

13. Time Line (cont) 300mya - Animals/Plants moved on land Oxygen in atmosphere created ozone that protected animals and plants from UV rays 250mya - Massive volcanic eruptions Led to extinction of 95% of living things Creation of Pangea 235mya - Dinosaurs began to rule Lukewarm blooded, allowed them to survive in hot, oxygen rich environment.

14. Time Line (cont) 180mya - Pangea breaks up. Dinosaurs survive 65mya - KT Boundary Asteroid/Comet impacts Mexico Volcanoes erupting in India Most dinosaurs go extinct

15. Time Line (cont) 50mya - Mammals began to flourish Uplift and Erosion shape surface of Earth 2mya - Human ancestors leave Africa Ice Ages send glaciers back and forth across the continents 10,000ya - Last Ice Age retreats Human civilization begins

16. The Future +15000y - New Ice Age Within the next 15000 years a new Ice Age will begin. +200my - New Super-Continent forms +2by - Mantle and Core cool Stops tectonic movement Stops magnetic field

17. Earth Earth is the 5th largest planet. 12,800km diameter. Not a perfect sphere Centrifugal force makes the circumference around equator bigger than circumference around poles. (difference of 67km) Oblique Spheroid

18. Earths Axis Earths axis is an imaginary line that runs through the Geographic North and South Poles. The Earth spins about this axis once every 23hours 56minutes. The axis is tilted at an angle of 23.5 from vertical. This tilt is responsible for the seasons.

19. Seasons The seasons have differing weather patterns for two reasons 1. The angle of the Suns rays varies from most direct in the summer (hotter) to least direct in the winter (cooler) 2. The length of day varies from longest in the summer to shortest in the winter, giving the Suns rays less time to warm the Earth. The Northern and Southern Hemispheres have opposite seasons.

21. Solstices The solstices occur on when the amount of daylight is the greatest or least and the angle of the Suns Rays are the most or least direct. Winter Solstice - December 21st Summer Solstice - June 21st

24. Equinoxes An equinox occurs when there is exactly 12hours of daylight and the Suns rays are pointing directly at the equator. Spring Equinox - March 21st Fall Equinox - September 23rd

26. Earths Structure Earth is comprised of several layers. These layers are separated due to their density. Crust Upper Mantle Lower Mantle Outer Core Inner Core

28. Crust The Crust is the layer of the Earth we all walk on. 0-35km below the surface of the Earth. Two different types Granite Crust - Covers continents, thicker Basaltic Crust - Ocean Floor, thinner Crust contains rock in all phases of the rock cycle.

29. Mantle The Mantle is the area of rock between the core and the crust. (35-3000km) The rock is plastic in characteristic and flows too slowly to be considered a liquid. The difference between the upper and lower mantle is due to the way seismic vibrations pass through. Seems to be pressure related.

30. Outer Core Liquid layer of Iron and Nickel located between the inner core and the lower mantle. 3000-5000km deep Predominantly responsible for Earths magnetic field due to the rapid movement of the liquid metal.

31. Inner Core The center of the Earth. Solid alloy of nickel and iron. 5000-6400km deep Thought to be hotter than the surface of the sun. (Remains solid due to immense pressure)

32. Earths Magnetic Field As a result of the rapidly spinning liquid metal found in the outer core, Earth has a magnetic field, similar to a giant bar magnet. This magnetic field protects us from harmful rays and particles emitted from the sun.

36. Magnetic Poles Just like a bar magnet, Earth has magnetic north and south poles. A compass is a small magnet that aligns its self to Earths magnetic field, always pointing to the North and South Magnetic Poles. A compass above either magnetic pole will point in random directions. These poles do not align with Geographic poles. They can move up to 15km a year.

37. The Moon The Moon is Earths only natural satellite. It is the fifth largest moon in the Solar System. The Moons orbit ranges from a distance 363,000km to 406,000km. The moon is about 3500km in diameter This gives the moon roughly 1/6th the gravity of here on Earth.

38. Moon (cont) The moon takes 27.3 days to orbit the Earth. As the Earth is also moving during this time the Moon completes its cycle of phases over a period of 29.5 days.

39. Structure of the Moon Like Earth, the Moon has a crust, mantle and core. Unlike Earth, only a small portion of the Moons core is still liquid. The Moon has cooled significantly since it was formed.

41. Surface of the Moon The Moons surface has several important features. Maria - dark, relatively featureless plains on the moon. Formed as lava filled depressions left by impacts. Terre - Lighter colored highlands of the moon Mountains exist only around the edges of Maria and were not formed by tectonic movement.

42. Surface of the Moon (cont) Regolith - the soil of the Moon Result of many impacts breaking up rock into very fine particles. Maria has 3-5m of regolith, Terre has 10-20m. Impact Craters - form as asteroids, meteors, and comets impact the Moon. Lack of atmosphere leaves these craters undisturbed.

44. Motion of the Moon If we could view the Earth moon system from above the North Pole, the moon would rotate around the Earth counterclockwise. It also rotates once about its axis, again in a counterclockwise motion.

46. Tides One of the most obvious effects of the relationship between the Moon and Earth are tides. Tides are the result of the gravitational pull of the Moon and the Sun on Earths oceans. They can cause the level of the ocean to change as much as 17 meters depending on the location

48. Types There are two types of tides. Spring tides occur when the Moon, Earth and Sun form a straight line. These tides are the most extreme, highest and lowest. Gravity of Sun and Moon work together. Neap tides occur when the Moon, Earth, and Sun form a right angle. These tides have the least variation between high and low tide. Gravity of Sun and Moon are work against each other.

51. Sides of the Moon Because the Moon rotates exactly once for each revolution around the Earth, the same side of the Moon always faces the Earth. We call this side the Near Side of the Moon. The Far Side of the moon is often incorrectly called the Dark Side of the Moon. The Far Side of the moon has almost no Maria. Likely due to lack of tidal forces from Earth.

54. Phases of the Moon Like any sphere lit by a single source, half of the moon is always dark. As the Moon spins around Earth, we see varying amounts of this lit portion. When the amount of the lit Moon we can see each night is getting larger the moon is considered to be waxing. The Moon is considered to be waning as the lit portion decreases each night.

55. New Moon The new moon occurs as the moon is between the earth and the sun. The new moon is not visible. It rises and sets with the sun.

56. Waxing Crescent Is the phase in between the New Moon and the First Quarter The edge of the Moon is on the right. They rise between sunrise and noon and set between sunset and midnight.

57. First Quarter The First Quarter occurs when the Moon and the Sun form a right angle with Earth. The curved side of the Moon is on the right. Rises at noon and sets at midnight.

58. Waxing Gibbous Occurs between the First Quarter and the Full Moon. The more rounded side is on the right. Waxing Gibbous moons rise between noon and sunset, and set between midnight and dawn.

59. Full Moon Full Moons occur when the Earth is between the Moon and the Sun. Full Moons rise at sunset and set at sunrise. A Blue Moon occurs when there are two Full Moons in one month.

60. Waning Gibbous The phase between a Full Moon and the Last Quarter. Gets a little smaller each night. The more rounded side is now on the left. Rises between sunset and midnight and sets between sunrise and noon.

61. Last Quarter Last Quarter occur when Moon Earth and Sun form right angle. The round side of the Moon is on the left. Rises at midnight and sets at noon.

62. Waning Crescent Phase between the Last Quarter and the New Moon. Edge of moon on the left Rises between midnight and sunrise, sets between noon and sunset.

63. Eclipses An eclipse occurs as the shadow of the Earth or Moon blocks the sun from the other. Because the Moon revolves around Earth at a slight angle, and is quite a distance from Earth, rarely does the shadow of one obscure the other.

64. Solar Eclipse Solar Eclipses occur as the Moon casts a shadow on the Earth. The Moons shadow has two parts Umbra - darker, center part of the shadow Penumbra - lighter outer part of the shadow An area that lies in the Umbra will see a full solar eclipse An area that lies in the penumbra will see a partial solar eclipse.

70. Occurrence Must occur during the New Moon phase. They occur somewhere on Earth about every 18 months. A total solar eclipse occurs in any given area of Earth about once every 370 years. As the shadow moves at 1700km/hr totality only lasts for at most 7.5 minutes.

71. Lunar Eclipse A lunar eclipse occurs as the Moon passes through the Earths shadow. Like solar eclipses, lunar eclipses vary according to the part of the shadow that Moon passes through. As the shadow occurs on the Moon it can be seen from the entire hemisphere that can view the Moon. Because of this Lunar Eclipses are seen more frequently


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