Timeline of Life

Early Earth and Oxygen

• Photosynthesis by early prokaryotes released oxygen into the atmosphere.
• Eukaryotes originated around 2.7 billion years ago.
• The Great Oxidation Event about 2.7 billion years ago led to the extinction of many organisms due to the toxic effects of oxygen.

Evolution of Life

• Mammals belong to the group of vertebrates, specifically amniotes (animals that lay eggs on land or retain eggs internally).
• Evolution of mammals can be traced through gradual changes in their skeletal structures and teeth.
• Prokaryotes were the earliest inhabitants of Earth.
• The age of the Earth is approximately 4.5 billion years.

Key Events in Earth's History

• The first multicellular eukaryotes appeared around 1.5 billion years ago.
• The oldest known fossil mentioned is a stromatolite from 3.5 billion years ago.
• The increase in atmospheric oxygen concentration began about 2.5 billion years ago.
• The Cambrian Explosion, a period of rapid diversification of life, occurred about 540 million years ago.
• Animals with jaws originated about 450 million years ago.
• The geological time scale used in the text is a system for dividing Earth's history into eons, eras, periods, and epochs.

Specific Organisms

• Prokaryotes were the sole inhabitants of Earth for more than 1 billion years.
• Stromatolites are layered structures formed by microbial mats, primarily prokaryotic bacteria.
• The oldest known fossil of jawed vertebrates dates back to 400 million years ago.
• The origin of multicellular eukaryotes is referred to as symbiosis.

"Evolutionary Timelines: From Multicellular Organisms to Single-Celled Lifeforms" - Test your knowledge on the timeline of life on Earth, from the emergence of multicellular organisms to the appearance of humans. Explore the origins of single-celled lifeforms and their pivotal role in evolution. Discover fascinating facts about the oldest fossil evidence and the timing of key milestones in the history of life.