1. The History of the Earth

2. Origin of the Universe The universe began about 14.4 billion years ago
The Big Bang Theory states that, in the beginning, the universe was all in one place
All of its matter and energy were squished into an infinitely small point, a singularity
Then it exploded

3. Origin of the Universe
The tremendous amount of material formed clouds of hydrogen gas. This was blown out by the explosion eventually formed into a star and galaxies
After about 10 billion years, our solar system began to form

4. Stars Stars, through nuclear fusion turn hydrogen into other elements
Therefore, Stars make elements
At the end of a Star’s life it runs out of hydrogen gas and the Star explodes called a Super Nova.

5. The Nebular Hypothesis
In cosmology, the Nebular Hypothesis is the currently accepted argument about how a Solar System can form

6. The Nebular Hypothesis
A large Molecular Gas Cloud or Nebula begins to condense
Most of the mass is in the center, and there is turbulence in the outer parts

7. The Nebular Hypothesis
The turbulent outer parts collect matter measuring meters across. Then,
Small chunks grow and collide, eventually becoming large aggregates of gas and solid chunks

8. The Nebular Hypothesis
Pictures from the Hubble Space Telescope show newborn stars emerging from dense, compact pockets of interstellar gas called evaporating gaseous globules

9. The Nebular Hypothesis
Gravitational attraction causes the mass of gas and dust to slowly contract and it begins to rotate
The dust and matter slowly falls towards the center. The Nebula Collapses and spins into a disc

10. Protostar
The center of the disc ignites into a star

11. False Color Image of Protostar
The multi-colored area shows a dust disk surrounding a newborn star
The red-orange area at the center represents the brightest region, which contains the young star
It is surrounded by the cooler, dusty disk, which appears as yellow, green and blue
The diameter of the disk is about 20 times larger than our entire solar system

12. (H atom + H atom = He atom + energy)
Stars
After sufficient mass and density was achieved in a star, the temperature rises to one million °C, resulting in thermonuclear fusion.
(H atom + H atom = He atom + energy)

13. Stars
Recall,
Stars, through nuclear fusion turn hydrogen into other elements
At the end of a Star’s life it runs out of hydrogen gas and the Star explodes into a Super Nova.
This spreads elements and gas all over the universe

14. Birth of the Solar System
Elements collide and form planets

15. Protoplanets
Gravitational forces allow the inner planets to accrue and compact solid matter (including light and heavy atoms)
Solar radiation from the star, blew gases (primarily hydrogen, helium) away from inner planets
These gases were collected and condensed into the outer gas giants (Jupiter, Saturn, Uranus, Neptune)
Beyond Neptune, ice and frozen gases form Pluto, Sedna and the Kuiper Belt Objects
Left-over debris form comets and asteroids

16. Birth of the Solar System
Planets orbit the star, called a Solar System

17. Start of Our Planets

18. Size of the Planets

19. Venus, Earth and Mars
These maps are color coded to display different elevations on the surface of each planet
Fig. 1.9

20. The Age of the Earth Earth is ~ 4,570,000,000 years old
Meteorites give us access to debris left over from the formation of the solar system
We can date meteorites using radioactive isotopes and their decay products

21. Bombardment From Space
For the first half billion years of its existence, the surface of the Earth was repeatedly pulverized by asteroids and comets of all sizes
One of these collisions formed the Moon

22. The Early Earth Heats Up
Three major factors that caused heating and melting in the early Earth’s interior:
1. Collisions (Transfer of kinetic energy into heat)
2. Compression
3. Radioactivity of elements (e.g. uranium, potassium, or thorium)

23. The Core
About 100 million years after initial accretion, temperatures at depths of 400 to 800 km below the Earth’s surface reach the melting point of iron
*In a process called global chemical differential, the heavier elements, including the melted iron, began to sink down into the core of the Earth, while the lighter elements such as oxygen and silica floated up towards the surface

24. Global Chemical Differentiation
This global chemical differential was completed by about 4.3 billion years ago, and the Earth had developed a inner and outer core, a mantle and crust

25. Chemical Composition of Earth
Each of the major layers has a distinctive chemical composition, with the crust being quite different from the Earth as a whole
Whole Earth:
Fe+O+Si+Mg = 93%
Crust:
Si+O+Al = 82%

26. Chemical Composition of Earth
Lithosphere: strong, rocky outer shell of the solid Earth including all the crust and the upper part of the mantle to a depth of ~100 km (forms the plates)
Asthenosphere: weak,ductile layer of the mantle beneath the lithosphere; deforms to accommodate the motions of the overlying plates
Deep Mantle: mantle beneath the asthenosphere (~400 to 2900 km in depth)
Outer core: liquid shell composed of mostly iron
Inner core: innermost sphere composed primarily of solid iron

27. Chemical Composition of Earth
Continents: Formed from solidified magma that floated up from the Mantle
Oceans and Atmosphere: Fluid and gaseous outer layers believed to have been created by out-gassing of gases and fluids from volcanic eruptions (in a process called volatile transfer)

28. The Evolving Atmosphere
Right after its creation, the Earth is thought to have had a thin atmosphere composed primarily of helium (He) and hydrogen (H) gases
The Earths gravity could not hold these light gases and they easily escaped into outer space
Today, H and He are very rare in our atmosphere

29. The Evolving Atmosphere
For the next several hundred million years, volcanic out-gassing began to create a thicker atmosphere composed of a wide variety of gases
The gases that were released were probably similar to those created by modern volcanic eruptions

30. The Evolving Atmosphere
These would include:
Water vapor (H2O)
Sulfur dioxide (SO2)
Hydrogen sulfide (H2S)
Carbon dioxide (CO2)
Carbon Monoxide (CO)
Ammonia (NH3)
Methane (CH4)
Note that oxygen (O2) gas is not created by volcanic eruptions

31. Creating the Oceans
It is hypothesized that water vapor escaping from the interior of the Earth via countless volcanic eruptions created the oceans (this took hundreds of millions of years)

32. Creating the Oceans
Astronomers also hypothesize that comets impacting the Earth were a major source of water that contributed to creation of the oceans
Remember, that comets are best described as “dirty ice balls”

33. Creating the Oceans
The earliest evidence of surface water on Earth dates back about 3.8 billion years

34. Geologic Time

35. A billion Year Old Earth
By 3.5 billion years ago, when the Earth was a billion years old, it had a thick atmosphere composed of CO2, methane, water vapor and other volcanic gases
By human standards this early atmosphere was very poisonous
It contained almost no oxygen
Remember, today our atmosphere is 21% oxygen

36. A billion Year Old Earth
By 3.5 billion years ago, the Earth also had extensive oceans and seas of salt water, which contained many dissolved elements, such as iron

37. A billion Year Old Earth
But most important, by 3.5 billion years ago, there was life on Earth

38. The Creation Of Life
These 3.5 billion year old fossilized algae mats, which are called stromatolites, are considered to be the earliest known life on earth
They are found in Western Australia

39. A billion Year Old Earth
These stromatolite fossils, found in Glacier National Park, half a planet away from Australia, also may be 3.5 billion years old

40. A billion Year Old Earth
Stromatolites are formed in shallow seas or lagoons when millions of cyanobacteria (a primitive type of bacteria) live together in a colony

41. Cyanobacteria
Cyanobacteria, commonly called blue-green algae, is a phylum of bacteria that obtain their energy through photosynthesis
This was the first life on Earth

42. Prokaryota Bacteria are cells without nuclei and are called Prokaryota
While prokaryotes are nearly always unicellular, some are capable of forming groups of cells called colonies

43. The Creation Of Life How do you create cyanobacteria?
The composition of the early atmosphere and oceans were conducive to the creation of primitive amino acids which are the building blocks of protein molecules, as demonstrated in this picture

44. Miller – Urey Experiment
Fifty years ago, Stanley Miller, a graduate student working with cosmologist Harold Urey, was able to create amino acids by exposing a gas that simulated the early Earth atmosphere to ultraviolet radiation and water

45. Oxygen
The ability of cyanobacteria to perform oxygenic photosynthesis is thought to have converted the early Earth atmosphere into an oxidizing one, which dramatically changed the life forms on Earth and provoked an explosion of biodiversity

46. Oxygen
By around 2.2 to 2.4 billion years ago, the Earth had developed an atmosphere that is very similar to today’s atmosphere (nitrogen and oxygen)

47. Banded Iron Formations
How do we know that there was no oxygen in the early Earth atmosphere?
Oxygen oxides native iron and created minerals such as hematite (iron oxide which is F2O3)
Simply put, water and oxygen creates rusts out of iron

48. Banded Iron Formations
Banded iron formations (also known as BIFs) are a distinctive type of rock often found in primordial sedimentary rocks
The structures consist of repeated thin layers of iron oxides, either magnetite or hematite, alternating with bands of iron-poor shale and chert

49. Banded Iron Formations
BIFs are primarily found in very old sedimentary rocks, ranging from over 3 to 1.8 billion years in age

50. Banded Iron Formations
It is hypothesized that the banded iron layers were formed in sea water as the result of free oxygen released by photosynthetic cyanobacteria combining with dissolved iron in the oceans to form insoluble iron oxides, which precipitated out, forming a thin layer on the seafloor

51. The Continents
By 2.5 billion years ago, the continents had been formed
The density of the continental crust (2.8 gr/cm3) is lighter that the crust found on ocean bottoms (3.2 gr/cm3), so the continents rise above the ocean floor
A question that remains unanswered is, when did plate tectonics start?

52. Geologic Time

53. Nucleus Bearing Cells Nucleus-bearing cells are called Eukaryotes
About 2.2 billion years ago, the first primitive Eukaryotes appeared on Earth
For 1.7 billion years, Eukaryotes slowly evolved and spread across the Earth

54. Nucleus Bearing Cells
Then, at the start of the Cambrian, 570 million years ago, there was an explosion in the diversity of life on Earth by Nucleus-bearing cells