Scientists have divided this timeline into huge “chunks”, or intervals, of time. The largest "chunk" of time is known as the Supereon. Supereons are broken down into smaller units of time called Eons. Eons are further divided into Eras, and Eras are divided into periods. The “chunks” are all divided by huge events that end one and begin another.
Since the Earth is so old, scientists describe most events in terms of “Million Years Ago” (MYA).
1. Cenozoic Era (65 MYA to present)
2. Mesozoic Era (250-65 MYA)
3. Paleozoic Era (544-250 MYA)
4. Precambrian Eon (4600-544 MYA)
The Precambrian Supereon makes up the first 4 billion years of our planet’s history, which is almost 90% of the earth’s entire history! The Precambrian Supereon began with the birth of the earth, and ended with an event called the “Cambrian Explosion”. During the Precambrian Supereon, the atmosphere and oceans formed, and marine life originated. We know this from fossils that date over 60 million years old. Some fossils include worms, jellyfish, corals, and other primitive invertebrates.
The end of the Paleozoic era brought on the beginning of the Mesozoic era, which was the era of dinosaurs and the first mammals! During this time, the super-continent “Pangea” also began to break up. The Mesozoic Era ended when a meteor hit the earth 65 MYA, killing many life forms, as well as making dinosaurs extinct.
This event marked the beginning of the Cenozoic Era, which is the age of mammals, birds, bony fish and flowering plants. The Cenozoic Era began 65 million years ago and has not ended yet. During this era, a number of mountain ranges were formed. Some of these were the Alps, Andes, and Himalayas. Along with mountain ranges, some volcanoes were formed. The animals and plants that we are familiar with today came in to existence during this period, including human beings.
We humans are very new to planet earth. The first human ancestor was on earth only 2 MYA, and the first modern human was on earth only 0.4 MYA!
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