Humans and other organisms did not suddenly appear on Earth; instead, they evolved from earlier organisms. The first life forms appeared about 4 billion years ago and were microscopic, single-celled organisms. Earth started out as a jumble of gases and inorganic materials that later reacted together and formed organic materials, which made way for prokaryotic cells and later eukaryotic cells to form. We know this by looking at the fossil record, and we measure the age of the fossil through absolute and relative dating
RNA World Hypothesis: RNA was the first genetic material to appear on earth.
Last Universal Common Ancestor (LUCA): A prokaryotic cell that paved the way for all life on Earth to form.
Oxygen Catastrophe: As some early cells began making their own food via photosynthesis, cells that could not tolerate living in an oxygen environment(because oxygen is a waste product of photosynthesis)died, but there were also cells that evolved to use the oxygen for things like cellular respiration.
Endosymbiosis: Formed when an organism lives within another organism.
Fossil: What’s left of an organism after it has died, usually the bones or teeth. Even though the soft parts of the body often decompose soon after an animal’s death, the hard parts of the body can leave an imprint on rock or dirt, which means that the imprinted rock can be found millions of years later, after everything else has decomposed.
Relative Dating: If the fossil is lower in the rock, then the fossil is older. This does not give an exact age to the fossil.
Absolute Dating: By understanding a half-life of carbon-14, scientists can measure the amount of carbon-14 left in an organism to figure out how old it is.
Half-Life: Time it takes for 50% of atoms to decay.
Here is a figure depicting the history of the Earth, displaying each milestone
Notice how relatively recent humans' appearance onto Earth was, and how much time passed by before photosynthesis began on Earth.
Ma=million years ago
Ga=billion years ago
Living things are made up of organic molecules. The first organic molecules were thought to have formed from lightning passing through Earth’s early atmosphere.
According to the RNA world hypothesis, RNA was the first organic molecule to evolve.
Of the different early cells and molecules, scientists think that all life today evolved from one cell called the
Last Universal Common Ancestor (LUCA).
About 2.5 billion years ago,the oxygen catastrophe took place.
Eukaryotic cells probably evolved about 2 billion years ago by forming endosymbiosis (plural of endosymbiosis).
Fossils are used to piece together the history of life on Earth. There are two ways to determine how old the fossil is:
When an organism is alive, it has a certain percentage of carbon-14 atoms. Once the organism has died, the number of carbon-14 atoms decays over time.
We can determine how long ago the organism died if we know the half-life of carbon-14. The half-life of carbon-14 is about 5,730 years. Taking the fossil remains, we could figure how much carbon-14 is in the remains and compare that amount with how much carbon-14 is in a living organism.
We can then figure out how many half-lives the remains went through. When we have that information, we can multiply the number of half-lives with how many years are in a half-life to determine the approximate time of when the organism died.
Carbon dating is important to figuring out the age of the fossil. However, after a certain point, the amount of carbon-14 remaining is so small that it is undetectable, or not enough to predict how many half lives an organism has gone through. Therefore, carbon dating is only useful for dating back 60,000 years.