Atmosphere timeline by Gracen Marshall

4.6 billion years ago

marshag26 — 2025-07-07 22:35:22 UTC

Earth formed about 4.6 billion years ago from hot gases and solids. At first, it had almost no air, and the surface was melted rock. As the Earth cooled down, volcanoes released gases that made the first atmosphere. This air had gases like hydrogen sulfide, methane, and a lot more carbon dioxide than today. After around 500 million years, Earth cooled enough for water to gather on the surface.

The Archean Eon (4 to 2.5 billion years ago)

marshag26 — 2025-07-07 22:56:22 UTC

The Archean Eon had little oxygen and much more carbon dioxide and methane than today. These gases kept Earth warm even with a weaker Sun. Hydrogen escaped into space, helping oxygen build up. Temperatures ranged from 0°C to 40°C. Scientists know more now, but many details are still unclear. A long time ago, during the Archean Eon, Earth was covered in a thick, hazy air with no oxygen to breathe. Oxygen only existed in things like water. In the oceans, simple chemical changes turned carbon into tiny living cells that didn’t need oxygen they got energy from things like sulfur. About 2.7 billion years ago, tiny blue-green organisms called cyanobacteria lived in the oceans. They used sunlight, water, and carbon dioxide to make oxygen through photosynthesis. Over time, they made enough oxygen to fill about 1% of today’s air level. Today’s air has 21% oxygen. cite https://www.science.org/doi/10.1126/sciadv.aax1420

2.6 bya- 400 million years ago

marshag26 — 2025-07-07 23:44:11 UTC

Life and Earth’s air changed together. Tiny organisms that used sunlight made oxygen. Over time, this oxygen reacted with methane, clearing the thick haze. Around 2 billion years ago, the sky turned blue. After about 300 million years, there was enough oxygen to combine with iron from in the ground, to create rocks that were colored red called redbeds. Scientists study these to learn about Earth’s early air.

400 mya- 290 mya

marshag26 — 2025-07-07 23:49:54 UTC

This time frame was also known as the Carboniferous period. During the Carboniferous Period, plants covered the land and changed the air. About 350 million years ago, oxygen levels were around 20%, like today, and later rose to about 35%. Between 318 and 299 million years ago, huge forests and swamps grew. Normally, when plants die, they break down and release carbon dioxide. But in the swamps, dead plants were buried and didn’t decay, so less carbon dioxide went into the air. This made the Earth cooler.

290 mya- present

marshag26 — 2025-07-07 23:53:18 UTC

This time frame is known as the Modern atmosphere. For most of the last 290 million years, Earth was alot warmer than it is today. From 200 to 45 million years ago, there was little or no ice at the poles, and winters were mild. Many plants and animals lived even in polar areas. The warmest time was the Eocene Epoch. Palm trees grew in Canada, and redwood forests and alligator like animals lived near the North Pole. The Arctic Ocean wasn't frozen. Because the Eocene was not that long ago, scientists still find clues about the air, climate, and life from that time.