Timeline of Earth
Introduction
The timeline of Earth reveals the planet's dynamic history, from its formation to the development of complex life. Over billions of years, geological, atmospheric, and biological transformations have shaped the world we know today.
Timeline
Geological Eras and Key Events
| Era/Eon | Time Period | Key Events |
|---|---|---|
| Hadean Eon | 4.6 - 4 billion years ago | Formation of Earth<br>Earth forms from cosmic dust and gas; intense volcanic activity and meteor impacts. |
| Archean Eon | 4 - 2.5 billion years ago | Origin of Life<br>First simple life forms (prokaryotic cells) appear in the oceans. |
| Proterozoic Eon | 2.5 billion - 541 million years ago | Oxygenation Event<br>Photosynthesis by cyanobacteria increases atmospheric oxygen. |
| Phanerozoic Eon | 541 million years ago - Present | Diverse Life<br>Major evolutionary events and the rise of complex organisms. |
| - Paleozoic Era | 541 - 252 million years ago | Cambrian Explosion<br>Sudden increase in the diversity of life forms. |
| - Mesozoic Era | 252 - 66 million years ago | Age of Reptiles<br>Dinosaurs dominate the land; first mammals and birds appear. |
| - Cenozoic Era | 66 million years ago - Present | Mammalian Evolution<br>Mammals diversify and humans emerge. |
Detailed Timeline
Hadean Eon (4.6 - 4 billion years ago)
- Formation of Earth: The planet forms from the accretion of dust and gas in the solar nebula.
- Early Atmosphere: A dense, toxic atmosphere composed of volcanic gases envelops the planet.
- Lunar Formation: The Moon is created following a massive collision with a Mars-sized body.
Archean Eon (4 - 2.5 billion years ago)
- First Continents: Small proto-continents begin to form as the Earth's crust cools and solidifies.
- Origin of Life: Simple prokaryotic cells, such as bacteria, emerge in the oceans, marking the beginning of life on Earth.
- Stromatolites: These layered, microbial-formed structures provide some of the earliest evidence of life.
Proterozoic Eon (2.5 billion - 541 million years ago)
- Great Oxygenation Event: Cyanobacteria produce oxygen through photosynthesis, transforming the atmosphere and enabling aerobic life.
- Multicellular Life: The first multicellular organisms begin to evolve, setting the stage for complex life forms.
- Rodinia Supercontinent: The assembly of one of Earth's earliest supercontinents influences global climate and geology.
Phanerozoic Eon (541 million years ago - Present)
Paleozoic Era (541 - 252 million years ago)
Cambrian Period (541 - 485 million years ago)
- Cambrian Explosion: A rapid diversification of life occurs, with most major animal phyla appearing in the fossil record.
- First Shells and Exoskeletons: Organisms develop hard parts, leading to better fossil preservation.
- Trilobites: These early arthropods become one of the most iconic groups of Cambrian fauna.
Ordovician Period (485 - 444 million years ago)
- Marine Biodiversity: Oceans are filled with diverse life forms, including brachiopods, mollusks, and the first coral reefs.
- First Vertebrates: Jawless fish emerge, representing the earliest vertebrates.
- Ordovician-Silurian Extinction: A major extinction event wipes out approximately 85% of marine species.
Silurian Period (444 - 419 million years ago)
- Terrestrial Colonization: The first plants and arthropods begin to colonize land.
- Evolution of Jaws: Fish evolve jaws, leading to a significant evolutionary advantage in predation.
- Eurypterids: Also known as "sea scorpions," these large arthropods dominate Silurian waters.
Devonian Period (419 - 359 million years ago)
- Age of Fishes: Fish diversify dramatically, including the rise of lobe-finned and ray-finned fish.
- First Amphibians: Tetrapods make the transition from water to land, evolving from lobe-finned fish.
- Early Forests: The first large trees and forests appear, transforming terrestrial ecosystems.
- Devonian Extinction: A series of extinction events severely affects marine life, including many fish and reef-building organisms.
Carboniferous Period (359 - 299 million years ago)
- Coal Forests: Vast swampy forests of ferns, horsetails, and lycophytes dominate the landscape, leading to extensive coal deposits.
- Amphibian Diversification: Amphibians thrive and diversify in the humid, forested environments.
- Reptiles Emerge: The first true reptiles appear, marking the beginning of the amniote lineage.
- Insect Gigantism: High oxygen levels support the existence of giant insects and arachnids.
Permian Period (299 - 252 million years ago)
- Pangaea Formation: The supercontinent Pangaea forms, dramatically affecting climate and biodiversity.
- Reptile Evolution: Reptiles diversify, including the ancestors of mammals and dinosaurs.
- Permian-Triassic Extinction: The largest extinction event in Earth's history occurs, wiping out approximately 90% of marine species and 70% of terrestrial vertebrates.
Mesozoic Era (252 - 66 million years ago)
Triassic Period (252 - 201 million years ago)
- Recovery and Radiation: Life gradually recovers from the Permian extinction, leading to new evolutionary radiations.
- First Dinosaurs: Dinosaurs emerge and begin to dominate terrestrial ecosystems.
- First Mammals: Small, early mammals evolve from synapsid ancestors.
- Pterosaurs: The first flying vertebrates take to the skies.
Jurassic Period (201 - 145 million years ago)
- Dinosaur Dominance: Dinosaurs become the dominant land animals, with giant sauropods and fearsome theropods.
- Ocean Reptiles: Marine environments are populated by large reptiles like ichthyosaurs and plesiosaurs.
- First Birds: Avian dinosaurs, or early birds, make their first appearance, evolving from theropod dinosaurs.
- Cy