Roughly 4.6 billion years ago, Earth would gain its first atmosphere, yet this was an atmosphere that was completely unlike the atmosphere we know today. Today’s oxygen-rich atmosphere we’re familiar with didn’t form until the Proterozoic, between 2,500 and 541 million years ago, when oxygen-producing bacteria killed off much of the previously thriving life from the preceding Archean.

This, along with studies of massive insects such as the 75 cm wingspan Meganeuropsis permiana dragonflies from the Permian, and reconstructed temperature, oxygen, and carbon dioxide levels via paleoclimatology show periods during which Earth’s atmosphere and accompanying climate would be unrecognizable to us humans.

Human history covers only a minuscule fraction of Earth’s history during arguably one of the latter’s coolest, least eventful periods, and yet anthropogenic (man-made) climate change now threatens to rapidly change this. But wait, how do we know what the climate was like over such vast time scales?  Let’s take a look into how we managed to reconstruct the Earth’s ancient climate, and what these findings mean for our prospects as a species today.

Welcome to the Holocene

The current geological era is called the Cenozoic (also known as the Age of Mammals), which encompasses 66 million years, divided into three periods:

  • Paleogene: 66 – 23.03 million years ago (Mya)
  • Neogene: 23.03 – 2.58 Mya
  • Quaternary: 2.58 Mya – today

The Quaternary forms roughly the period in which recognizable humans existed and consists of two epochs:

  • Pleistocene (2.58 Mya – 11,700 ya)
  • Holocene (11,700 – today)

Some have proposed we recognize a new geological epoch called the Anthropocene (‘human epoch’), which would be defined as the epoch in which human activity first began to leave significant traces in the geological record. Although still the subject of intense debate, the search is on to find a so-called ‘golden spike’ in the geological record that may consist out of radionucleotides, heavy metals, fly ash and similar finds which would be indicative of the rise of human activity during the early 20th century.

If the Anthropocene becomes the new current epoch, its beginning would likely be placed around the 1950s. Yet the Holocene and to some extent the Pleistocene are probably our best indicators for what counts as the current ‘normal’, as far as Earth’s current climate and global temperatures goes, and what would be the result of…

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