Biology - Major Life Events

What was the first major event in Earth’s history related to life?

The first life (prokaryotes) appeared — about 3.5 billion years ago.

What type of organisms were the first life on Earth?

Single-celled prokaryotes living in oceans.

What was the second major event in the history of life?

Atmospheric oxygen appeared — about 2.6 billion years ago.

What caused oxygen to appear in Earth’s atmosphere?

Photosynthetic bacteria released oxygen as a byproduct.

What was the third major event in the history of life?

The first eukaryotes evolved — about 1.8 billion years ago.

How did eukaryotic cells form?

Through endosymbiosis, when larger cells engulfed smaller bacteria that became organelles.

What was the fourth major event in the history of life?

Multicellularity evolved — about 1.3 billion years ago.

What did multicellularity allow organisms to do?

Form larger, more complex bodies made of specialized cells.

What was the fifth major event in the history of life?

Animals developed — about 600 million years ago.

Where did the first animals evolve?

In the ocean.

What was the sixth major event in the history of life?

Plants and fungi colonized land — about 500 million years ago.

What adaptations allowed plants to move onto land?

Roots, waxy cuticles, and vascular tissues.

What was the seventh major event in the history of life?

Animals moved onto land — about 450 million years ago.

Which animals were among the first to live on land?

Arthropods and early vertebrates.

What was the eighth and most recent major event in the history of life?

Humans evolved — about 200,000 years ago.

Where did modern humans first appear?

In Africa, later spreading worldwide.