Earth and Life Change Together
- Earth & Space
- Ages 14–18 · Grades 9–12
What you’ll find out
- Photosynthesising cyanobacteria oxygenated the atmosphere, leaving banded iron formations and building the ozone layer.
- Land plants created soils, changed the shape of rivers and drew down carbon dioxide, cooling the climate.
- Changes in Earth’s systems, such as massive eruptions and an asteroid impact, have in turn redirected evolution.
No sign-up and no real names. In the lesson you check your understanding as you read, and practise until it sticks.
How life changed the air
Earth’s surface and the living things on it have shaped each other for billions of years. Earth’s early atmosphere contained almost no free oxygen. Probably more than 2.7 billion years ago, cyanobacteria began photosynthesising in shallow seas. They built layered mounds called stromatolites. Their waste product, oxygen, first reacted with dissolved iron, forming rusty bands in rock called banded iron formations. Once the iron was used up, oxygen began to build up in the air. This Great Oxidation Event began about 2.4 billion years ago. Later, oxygen in the upper atmosphere formed the ozone layer. By blocking harmful ultraviolet light, it helped life move onto land.
How life changed the land
Life has reshaped Earth’s land surface too. For most of Earth’s history, the continents were bare rock and sand, with no soil as we know it. Plants began to colonise land about 470 million years ago. Their roots and the acids they released broke rock down faster. Dead plant matter mixed with the rock fragments to build soil. Roots also held riverbanks together, so single winding channels became common. As forests spread, they drew carbon dioxide from the air and helped cool the climate. Buried forest remains later became coal. The influence runs both ways. Volcanic eruptions and an asteroid impact have caused mass extinctions. The asteroid ended the age of the dinosaurs, 66 million years ago.
Curriculum links: NGSS HS-ESS2-7 · England KS4: Chemistry · NCERT Geography, Class 11