Lecture notes
Complete Geological Time Scale
- Module
- Life On Earth (GS10720)
- Institution
- Aberystwyth University (UWA)
A time scale containing all major eon, eras and ages with dates and notable events
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The Archean Eon was the second eon of the Earth's history, and it lasted from approximately 4 billionyears ago to 2.5 billion years ago. It was a time of great change and transformation for the young
planet, as it was undergoing rapid cooling and solidification, and the first life forms were beginning to
emerge. Here are the main stages and ages of the Archean Eon:
1. Eoarchean (4.0-3.6 billion years ago): This was the earliest period of the Archean Eon, and it was
characterized by intense volcanic activity, the formation of the first continents, and the emergence of
the first life forms.
2. Paleoarchean (3.6-3.2 billion years ago): During this period, the Earth's crust was still undergoing
intense volcanic activity, and the first evidence of plate tectonics began to emerge.
3. Mesoarchean (3.2-2.8 billion years ago): This period was marked by the continued evolution of life
forms, including the emergence of photosynthesis, which helped to oxygenate the Earth's atmosphere.
4. Neoarchean (2.8-2.5 billion years ago): This was the final period of the Archean Eon, and it was
characterized by the emergence of more complex life forms, such as eukaryotic cells, and the
continued evolution of the Earth's crust and atmosphere.
Throughout the Archean Eon, the Earth underwent significant changes, including the formation of the
first continents, the emergence of life, and the evolution of the planet's geology and atmosphere. These
changes set the stage for the subsequent eons of the Earth's history and helped to shape the planet
into the complex and diverse ecosystem that we know today.
,The Paleoproterozoic is a geologic eon that lasted from approximately 2.5 to 1.6 billion years ago. It is
the second eon of the Proterozoic Eon and followed the Archean Eon. During the Paleoproterozoic, the
Earth underwent significant changes, including the emergence of the first continents and the evolution
of life. Here are the main stages and ages of the Paleoproterozoic Eon:
1. Siderian (2.5-2.3 billion years ago): This period was characterized by the formation of the first stable
continents, the evolution of photosynthetic organisms, and the build-up of oxygen in the Earth's
atmosphere.
2. Rhyacian (2.3-2.05 billion years ago): During this period, the Earth's crust underwent significant
tectonic activity, resulting in the formation of large basins and mountain ranges. The evolution of life
continued, and the first evidence of sexual reproduction emerged.
3. Orosirian (2.05-1.8 billion years ago): This period was marked by the continued evolution of life,
including the emergence of multicellular organisms. The Earth's atmosphere became more oxygenated,
leading to the formation of a protective ozone layer.
4. Statherian (1.8-1.6 billion years ago): During this period, the Earth underwent a period of relative
stability, with little major tectonic activity. The evolution of life continued, with the emergence of more
complex organisms such as algae and fungi.
Overall, the Paleoproterozoic Eon was a time of significant change and evolution for the Earth, with the
emergence of stable continents, the evolution of life, and the build-up of oxygen in the Earth's
atmosphere. These changes set the stage for the subsequent eons of the Earth's history, including the
Mesoproterozoic and the Neoproterozoic.
, The Mesoproterozoic is a geologic eon that lasted from approximately 1.6 to 1.0 billion years ago. It
followed the Paleoproterozoic and preceded the Neoproterozoic. During the Mesoproterozoic, the Earth
underwent significant changes, including the continued evolution of life and the formation of
supercontinents. Here are the main stages and ages of the Mesoproterozoic Eon:
1. Calymmian (1.6-1.4 billion years ago): During this period, the Earth underwent a period of relative
stability, with little major tectonic activity. The evolution of life continued, with the emergence of new
groups of organisms such as dinoflagellates and ciliates.
2. Ectasian (1.4-1.2 billion years ago): This period was marked by the formation of the supercontinent
Nuna, which included most of the landmasses of the Earth at the time. The Earth's climate was
relatively stable, with no major glaciation events.
3. Stenian (1.2-1.0 billion years ago): During this period, the Earth underwent significant tectonic
activity, resulting in the formation of new mountain ranges and the breaking apart of supercontinent
Nuna. The evolution of life continued, with the emergence of new groups of organisms such as red and
green algae.
Overall, the Mesoproterozoic Eon was a time of continued evolution and change for the Earth, with the
formation of the supercontinent Nuna and the emergence of new groups of organisms. These changes
set the stage for the subsequent eons of the Earth's history, including the Neoproterozoic and the
Phanerozoic.
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