1. Earth’ s Early History

2. Formation of the Earth The Earth is 4.6 billion years old.
The Earth was made of large pieces of cosmic debris that stuck together.
The Earth was hit with many large objects, which generated enough heat to melt the Earth

3. Formation of the Earth’s Crust
The liquid crust separated according to density.
Heaviest metals settled to form the core
The metals are radioactive and create enough heat to keep the middle layer liquid.
The middle weight metals became the crust and the mantle.
The lightest weight elements became the atmosphere – hydrogen and nitrogen

4. The Early Atmosphere The early atmosphere did not have any oxygen.
Hydrogen cyanide – very toxic
Carbon dioxide- suffocates people
Carbon monoxide- suffocates people
Nitrogen – harmless
Hydrogen sulfide – toxic in large quanities
Water – harmless.

5. Changes Early Earth was rocked with violent volcanic activity.
About 3.8 billion years ago, the Earth was cool enough for water to stay as a liquid.
This provided a place for life to appear.

6. Formation of Organic Molecules
Organic molecules are carbon-based molecules that are required for life.
Many scientists have created organic molecules from conditions similar to life on the early Earth.
Amino acids from lightning strikes
Microspheres similar to cell membranes
DNA and RNA appearing

7. Amino acids from lightning
Amino acids are needed for making protein.
The early atmosphere when lightning is present can have amino acids form from chemicals.
In 1995, scientists found that cytosine and uracil can form in the condition like early Earth.

8. Microspheres
Cell membranes are made of lipids with proteins embedded in the membrane.
These spheres form spontaneously when lipids and proteins are present.

9. Evolution of RNA and DNA
Scientists couldn’t figure out how to get RNA and DNA to evolve because RNA is needed to make DNA which makes RNA.
About 10 years ago, scientists found that RNA can make RNA.
Currently, scientists think RNA formed first and replicated itself.
DNA came later. No one is quite sure how the DNA appears.

10. Oxygen Production: 1st environmental crisis
By 2.2 billion years ago, photosynthetic organisms were living in the ocean.
Oxygen gas, a product of photosynthesis, was building up in the water of the ocean.
The first organisms were anaerobic.
Oxygen was a poison to those organisms.
Some organisms began using oxygen to create energy
Aerobic life evolved to survive in an oxygen-rich environment.

11. Endosymbiotic Theory: Life as we know it.
Modern plant and animal cells have two sets of genetic material
The genes found in the nucleus
The genes found in the mitochondria and/or chloroplasts
Scientists believe that early bacteria were taken in by other cells.
Modern cells are a combination of two bacteria that are supporting each other.