Science – Prehistoric Times – What Was the Archean Period?

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Prehistoric Times

The Archean (ar-KEE-uhn) Period started about 4 billion years ago and lasted until about 2.5 billion years ago. That’s a looooooooot of zeroes! It was so long ago, that there isn’t much left to find from that time period. But we do know that life probably started during the Archean, and we’ve found a few fossils of bacteria that may be from that time!

Fancy Science Words
Archean PeriodThe period of time between 4 billion to 2.5 billion years ago when life may have begun on earth
Greenhouse GasesGases like carbon dioxide and methane that trap heat in the atmosphere and warm the planet
ZirconA very tough crystal that forms as magma or lava cools
Sedimentary RockRock formed by sand and other small particles as they settle beneath the water
ErosionThe process of water or wind wearing away rocks or soil over time
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What Did the Earth Look Like?

Since there isn’t much left over from the Archean, it’s hard to say exactly what the earth looked like then. The atmosphere was probably thick with greenhouse gases like methane and carbon dioxide. There were probably continents then, but they would have been smaller than today. We do know that there were oceans of water because 4-billion-year-old zircon crystals have been found in sedimentary rocks.

How does that show us that the earth had water? Well, zircon crystals need extreme heat and pressure to form. They probably formed after giant meteorites hit the earth and turned the land into oceans of lava. Water erodes, or wears away, rocks and creates sand. When sand settles together underwater, it can form a sedimentary rock. So, for zircon crystals to get into sedimentary rock, they had to be eroded away by water.

Science Facts
Did you know that about 37% of methane in the atmosphere comes from cows? They should really cover their mouths when they burp!
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What Was the Climate Like?

The sun was much younger during the Archean than it is now. That means that it wouldn’t have been as hot, and there would have been less light. Because the sun was so much weaker, the earth should have frozen solid during that time, but it didn’t! We aren’t totally sure why, but one theory is that all of the greenhouse gases in the atmosphere kept the planet warm. Actually, the earth was much hotter than it is today. The temperature was probably somewhere between 130-175° F (55-80° C)!

Fancy Science Words
Single-celled OrganismsLiving creatures whose bodies are made of just one cell
ArchaeaVery tough single-celled organisms. Maybe the first things to ever live
Anaerobic BacteriaBacteria that don’t need oxygen to live
PhotosynthesisThe process some living things use to make food from sunlight, carbon dioxide, and water
ChemosynthesisThe process some living things use to make food from rocks and minerals
Proterozoic PeriodThe time period from about 2.5 billion to 541 million years ago
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What Lived Then?

There wasn’t much oxygen, and it was really hot, so only single-celled organisms could live during the Archean. Things like archaea (ar-KEE-uh) and anaerobic (an-uh-ROH-bic) bacteria. Archaea are kind of like bacteria. Some can make food by using photosynthesis or chemosynthesis. Archaea are really tough and can survive in harsh environments. Anaerobic bacteria don’t need oxygen to survive, which is why they would have been able to live during the Archean Period.

Science Facts
There are millions of different types of bacteria on earth. Some can make you sick, and some can make you healthy! They help you digest food, and they turn dead leaves into soil. Bacteria are everywhere!

That’s it for the Archean Period. Next time, we will talk about the Proterozoic (proh-ter-uh-ZOH-ic) Period. Life on earth is about to get more interesting!

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