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4.5 BYA: Formation of Planet Earth - Start
Earth begins as a conglomeration of rocks and dust particles that coalesce into a molten, firey planet. It takes millions of years for Earth to cool down to a temperature where the crust forms and water vapor in the air condenses to form the liquid water of Earth's oceans. This cooling process allowed for the beginning of the chemical reactions that would ultimately form life. Watch Me Take 40 steps -
3.5 BYA: Earliest Fossil Record of Prokaryotic Cells
Life arose from chemical systems that could make copies of themselves and keep all of their components inside some type of structure. A molecule like RNA would meet the first requirement, surround that RNA with a thin membrane and you have the earliest forms of life. The first life formed on Earth without oxygen. These simple prokaryotic cells got their energy by breaking down minerals in Earth's early oceans. Watch Me Take 45 steps -
3.0 BYA: Oxygen Levels Lead to the Evolution of Photosynthesis
As oxygen levels increase in the atmosphere, early cellular organisms, called cyanobacteria develop the adaptation of photosynthesis. This process allows cells to use the excess oxygen to produce huge amounts of energy, speeding up the process of evolution.- Mark this from 3.5 BYA to 2.5 BYA with a bracket
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2.5 BYA: Earliest Fossil Eukaryotes
The increase in oxygen concentration in the atmosphere led to the adaptation of more complex cells that could derive their energy from oxygen. This energy boost allowed cells to grow larger and more complex. During this time small O2 dependent bacteria was engulfed by a larger cell. The bacterium provided both cells with more than enough energy, and from then on the two evolved together creating a group of cells called eukaryotes. Watch Me Take 40 Steps -
700 MYA: First Fossilized Evidence of Multicellular Organisms
Prokaryotes and eukaryotes existed as single-celled organisms until, likely due to an error in cell division, two eukaryotic cells did not separate after cell division. Overtime, a mass of identical cells became better adapted through cell specialization, the process where individual cells in an organism perform different functions. These small, soft-bodied organisms lived in the oceans, resting on the sea floor or floating near the surface where they could get sunlight. Take 5 Steps -
600 MYA: Ice Age
During this ice age, many species go extinct. The species that survive are left in an environment with ample resources and and increased amount of oxygen. Take 4 Steps -
500 MYA: First Vertebrates in the Fossil Record & The Cambrian Explosion
During this time, organisms were developing more complex body plans (muscles, segmented bodies, limbs, exoskeletons, shells, etc.) to help them fill new environmental roles that did not previously exist (predator/prey). All major animals groups that exist today can trace their development back to this time including the first vertebrates. Complex body designs were due to developments in genes which made these body plans successful adaptations. Watch Me 5 Steps -
416 MYA: First Insects in Fossil Record
50 million years after plants moved onto land, animals followed to escape predators in the oceans. The most successful animals dealt with the land's lack of water by developing waterproof exoskeletons and jointed legs. Before too long, insects had developed wings, another example of an adaptation that allowed species to exploit new environmental roles. Due to the high levels of oxygen in the atmosphere, some of these ancestral insects grew to be enormous. Take 8 Steps -
245 MYA: Permian Mass Extinction
The Permian Mass Extinction is the worst extinction in Earth's history (yup! There have been 5 mass extinction events!). Following a burst of volcanic activity, molten rock covered large areas and huge amounts of CO2 blanketed the planet, driving the temperature up. Sulfuric compounds from the volcanoes acidified the oceans and cause acid rain. 90% of all species went extinct. Watch Me Take 0.25 Steps -
230 MYA: First Dinosaurs in the Fossil Record
Following the Permian Mass Extinction where 96% of animal species went extinct, surviving species of reptiles experienced great diversification over the next 10 million years. Watch Me Take 2 Steps -
200 MYA: Earliest Mammals in Fossil Record
Early mammals appear in the fossil record as small, insect-eating, furry creatures that give birth to live young. Mammals diversified after the extinction of the dinosaurs to include a group called primates. This group gave rise to lemurs, monkeys, apes, and eventually our hominid ancestors. Watch Me Take 4 Steps -
65 MYA: K-T Extinction
The most famous of the five mass extinctions, this marks the end of the Cretaceous period. An asteroid hits Earth in the Yucatan Peninsula off Mexico causing 2/3 of all land species to go extinct, and ending the reign of the dinosaurs. The only surviving lineage of dinosaurs are ancestral birds, relatives of the birds that exist today. Watch Me Take 3 steps -
1.8 MYA: Earliest Homo erectus Fossils
Our ancestors, Homo erectus, were tall and thin, an adaptation for walking and running, which would have been useful for a group that relied on hunting, gathering, and scavenging to obtain food. All these activities also required a high degree of cooperation, favoring the evolution of ever-larger brains and the ability to communicate through spoken language. Watch Me
