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 blown out by the explosion eventually formed the stars and galaxies
After about 10 billion years, our solar system began to form

4. Birth of the Solar System
We know how the Earth and Solar System are today and this allows us to work backwards and determine how the Earth and Solar System were formed
Plus we can out into the universe for clues on how stars and planets are currently being formed

5. H atom + H atom = He atom + energy
The Sun
After sufficient mass and density was achieved in the Sun, the temperature rose to one million °C, resulting in thermonuclear fusion.
H atom + H atom = He atom + energy

6. Birth of the Solar System

7. Size of the Planets

8. 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

9. Geologic Time

10. 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

11. 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)

12. 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

13. 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

14. 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

15. 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)

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

17. Geologic Time

18. 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

19. 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

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

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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

27. 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

28. 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

29. 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)

30. 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

31. 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

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

33. 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

34. 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?

35. Geologic Time

36. 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

37. 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