Geologic Timelines
Time on the scale of a planet!
Slow change...
over eons...
Planet Earth has been around for billioins of years...and that's a lot of time to keep track of. The standardized geologic timescale used by historians and geologists breaks time down into 5 different catagories: Eons, Eras, Periods, Epochs, and Ages. The different catagories are for better understanding scales of time. The largest catagories, Eons and Eras, are for understanding big picture things about Earth in the realm of hundreds of millions to billions of years. The smaller scales, periods and Epochs, are for more specific details spaning thousands to a couple million years.
The Eons:
- Hadean - the initial formation of Earth from dust, gasses, and planetesimals into a stable core with a crust.
- Archean - the emergence of a primitive atmosphere and ocean, along with the earliest forms of microbic life.
- Proterozoic - the atmosphere developes, and with it the first oxygen dependant life and metallic ores/minerals as the planet "rusts."
- Phanerozoic - photosynthesis takes over the planet and rapid evolution happens, continents drift to form mountain ranges.
Featured Facts
"Plants developed photosynthesis in the Phanerozoic eon, which is what caused the atmosphere to fill with oxygen and the animals to evolve dependancy on it."
"There are missing chunks of history in the geologic record in many places; this is due to weathering, glaciers, or eventually tectonics as all land is eventually recycled into the Earth."
"The earliest animals all looked more like plants, as many of the features we associate with animals hadn't evolved yet."