Discover and read the best of Twitter Threads about #snowballearth

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2.4 billion years ago, Earth's atmosphere was free of oxygen. Iron didn't rust! Only anaerobic species could survive.

And then ... cyanobacteria evolved photosynthesis, and began to pump oxygen into the atmosphere.


🧵 1/n

#GreatOxygenationEvent… Image
Suddenly, iron dissolved in the oceans bonded with oxygen and precipitated, forming layers of rust on the ocean floor. The deposits got thicker and thicker, reaching 100s of meters. 60% of iron is mined from these layers! 2/n

#bandedironformations… Image
Methane was no longer stable: it reacted with oxygen to form CO2. Methane is a far more powerful greenhouse gas - so dropping methane levels triggered sudden cooling. The Earth froze over, with glaciers reaching as far as the tropics. 3/n

Read 6 tweets
It's chilly today but nothing like during #SnowballEarth – a deep freeze that took place about 720-640 million years ago. Carbon dioxide levels plummeted, #Earth cooled and was mostly covered in ice.
#nspoli #cbpoli #Novascotia #capebreton #NS #CB Image
We know about #SnowballEarth thanks to #geology. Glacial deposits - rocks that were left by glaciers - indicate there were glaciers at the equator at that time. If there were glaciers in #Earth's warmest areas, there were probably glaciers everywhere.
#nspoli #cbpoli #Novascotia Image
#SnowballEarth likely ended because volcanic eruptions under the ice put CO2 back into the atmosphere and warmed earth again. This facilitated the #CambrianExplosion ~541 million years ago, in which complex animal life forms appeared on Earth for the 1st time.
#nspoli #cbpoli Image
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