The air makers
Most scientists think that the first tiny sea plants made it possible
for life to come onto the land.
To live, plants and animals must take in a gas called oxygen. The tiny
sea plants and animals of billions of years ago got oxygen from the
water, just as fish and sea plants do today. But scientists think that
long ago there was no oxygen in the world’s air. So there were no land
plants or animals because there was no way for them to get oxygen.
When plants make their food—out of sunlight, water, and carbon dioxide
gas—they give off oxygen. The tiny sea plants of long ago gave off
tiny bubbles of oxygen. The bubbles rose to the top of the water and
burst. Tiny puffs of oxygen went into the air.
For millions and millions of years, billions and billions of tiny plants
put oxygen into the air. Finally, there was enough oxygen in the air so
that plants and animals could live on the land.
Scientists think that the first oxygen in the air came from tiny sea
plants.
