Atmosphere by Issabella Scoggins

4.6 billion years ago (Earliest atmosphere)

scoggii26 — 2025-07-23 03:47:44 UTC

When Earth formed 4.6 billion years ago, it had almost no atmosphere and a molten surface. As it cooled, gases from volcanoes created an early atmosphere with hydrogen sulfide, methane, and much more carbon dioxide than today. About 500 million years later, the surface cooled enough for water to collect.

4.0 bya-2.5 bya (The Archean Eon)

scoggii26 — 2025-07-23 03:50:45 UTC

Between 4 and 2.5 billion years ago, Earth’s atmosphere had no oxygen and was filled with methane, creating a thick haze. Simple life forms used chemicals like sulfur for energy. Later, Cyanobacteria began making oxygen through photosynthesis, slowly adding it to the atmosphere.

2.6bya-400mya

scoggii26 — 2025-07-23 03:51:12 UTC

As photosynthetic organisms produced oxygen, it reacted with methane in the air and changed the atmosphere. Around 2 billion years ago, the methane haze cleared, and the sky turned blue.

400mya-290mya (The Age of Oxygen)

scoggii26 — 2025-07-23 03:51:35 UTC

As land plants spread during the Carboniferous Period, they boosted oxygen levels in the atmosphere. Around 350 million years ago, oxygen reached 20% similar to today, and later climbed to 35% over 50 million years. Massive forests and swamps covered low areas. Plants like Cordaites, seed ferns, horsetails, and early conifers were common. Some lycopsids grew over 130 feet tall, while others stayed small like modern club mosses. As dead plants piled up in oxygen-poor swamps, less carbon combined with oxygen to form carbon dioxide. This drop in CO2 made Earth’s climate cooler.

290mya-present (Modern Atmosphere)

scoggii26 — 2025-07-23 03:51:50 UTC

For most of the last 290 million years, Earth was warmer than it is today. Between 200 and 45 million years ago, winters were mild and polar ice caps were small or missing. These warmer climates allowed many plants and animals to live in polar areas.

The Eocene Epoch was 55.8-33.9 million years ago and this was the warmest time in the past 65 million years. Palm trees grew as far north as Canada, and redwood forests reached the Arctic. The Arctic Ocean wasn’t frozen year-round, and animals like alligator relatives and early mammals lived in the north. Because this time is geologically recent, scientists can still study it to learn how climate and the atmosphere influenced life.