1. 14-2: EARTH’S HISTORY

2. The Formation of Earth
About 5 billion years ago, our solar system was a swirling mass of gas and dust
Over time, these materials collapsed inward forming the sun

3. Formation (cont.)
The planets are thought to have been made from 400 million years of constant collisions of dust and debris
Earth grew from these collisions
Thermal energy was released each time debris hit the Earth

4. Earth’s Age Earth is more than 4 billion years old (~4.6 b.y.)
How do we know?
Scientists have drilled holes down into Earth’s layers
More modern techniques established in the 20th century

5. Radiometric Dating A radioactive isotope is used to date material
The isotope is chemically unstable
Nucleus will release particles/radiant energy
Known as radioactive decay
Scientists will measure the half-life of a radioactive isotope
Length of time it takes for ½ of the isotope to decay
Half-lives vary from fraction of a second to billions of years

6. Half-live Graph

7. Example: C-14 Dating
Organic materials can be dated by comparing the amount of C-14:C-12
Living things take carbon into their bodies constantly, most of it in the form of C-12; a very small proportion of it is C-14, which undergoes decay

8. Example: C-14 Dating
When an organism dies, its uptake of carbon STOPS, and decay of the existing C-14 continues
Thus over time, the amount of C-14 declines with respect to the original amount of stable C-12
The half-life of C-14 is 5,730 years
C-14 is limited to organic remains less than 60,000 years old

9. Radiometric Dating (cont.)
The two isotopes that were used to date the Earth were:
Thorium-230 (75,000 years)
Uranium-238 (4.5 billion yrs)
Scientists found rocks + zircon crystals that are 4.2 billion years old - - so Earth must be older than that

10. The First Organic Compounds
All of the elements in organic compounds were thought to have existed on Earth and in the solar system when Earth formed
How did all these elements assemble into life forms?

11. Alexander I. Oparin In 1923, Oparin + Haldane
“Primordial Soup” model
Spontaneous origin from inorganic gases
They believed the atmosphere contained:
Ammonia – NH3
Hydrogen gas – H2
Water vapor – H2O
Methane gas – CH4

12. Oparin (cont.)
At high temps, these gases might have formed org. comps such as amino acids
When the Earth cooled, water condensed to form lakes and seas
compounds collected in water
over time, entered chemical reactions = fueled by lightning + UV radiation
These rxns could have ultimately resulted in macromolecules essential to life such as PROTEINS; building blocks for the 1st cells

13. Synthesis of Org. Compounds
Oparin never tested his hypothesis
In 1953, Miller + Urey tested Oparin’s hypothesis
Set-up this apparatus

14. Miller-Urey (cont.) Experiment:
Chamber with gases Oparin thought were on early Earth
Simulated lightning (spark from electrode)
Chemical reactions
Produced a variety of organic compounds, including AA

15. Miller-Urey (cont.)
Since the 1950s, scientists have continued to explore this idea of spontaneous origin
Have been able to produce AA, ATP, and DNA nucleotides
Suggests that there were many ways these compounds could have formed on young Earth

16. Miller-Urey (cont.) The gases included:
In more recent years, new hypotheses were proposed as to the atmosphere on early Earth
The gases included:
Carbon dioxide – CO2
Nitrogen – N2
Water vapor – H2O
Lab simulations showed the CO2 + O2 interfere with production of organic compounds
Organic compounds might have only been able to be produced in protected areas from the atmosphere…
Under WATER???

17. Org. Compounds beyond Earth
Another Hypothesis…
The organic compounds could have been carried to Earth by debris from space (meteorite)
Scientists hypothesized that these compounds were formed in space and could have accumulated on Earth’s surface

18. From Molecules to Cell-like Structures
Scientists (Sidney Fox) have tried to create the physical structures that may have given rise to the first cells
These cell-like structures were created in a lab from simple organic compounds
Microspheres
Spherical in shape
Composed of many protein molecules organized in a membrane
Coacervates
Collection of droplets from dissimilar substances (AA + sugars)

19. From Molecules to Cell-like Structures
For many years, it had been assumed that all cell structures and the chemical reactions of life required ENZYMES that were specified by the genetic information of the cell
Both microspheres and coacervates were spontaneously created in a lab and have several life-like properties, such as growth, reproduction, + taking in substances from their environment
Microspheres + coacervates do not have hereditary characteristics and thus aren’t LIVING!