Biology 106: History of Life on Earth, Domains, and Supergroups

This set pertains to terms and problems associated with the history of like on Earth, including mass extinctions, different eras, the rise of Eukaryotes, and fossils. There will also be terminology and definitions regarding bacteria and fungi, as well as the polyphyletic group collectively called protists.

When did life on Earth begin?

Earth began 3.5 to 4 billion years ago (most likely 3.8 bya). The earliest evidence of life comes from 3.5-billion-year-old fossils resembling modern cyanobacteria.

What is a fossil?

Fossils are preserved remains of past life. Rocks with fossils are often sedimentary (formed with layers). Organisms are buried quickly, and hard parts like bone are replaced by minerals. The deeper the fossil, the older it is.

What is radiometric dating?

Fossils can be dated using elemental isotopes found in accompanying rock. Radioisotopes spontaneously decay at a constant rate (the half-life). Age can be determined by measuring the amount of a given isotope or decay product.

When did the Big Bang occur?

13.7 billion years ago.

When did earth form?

4.5 billion years ago.

What are the Earth’s four eons? Which ones are Precambrian?

Hadean, Archaean, Proterozoic, and Phanerozoic. Precambrian includes Hadean,

Archaean, and Proterozoic.

What are Eons divided into?

Eons are divided into eras. Eras are divided into periods.

What was the Hadean eon?

The inhospitable beginning of Earth 4.5 bya until 3.8 bya. No ozone to shield from radiation, volcanic activity, earthquakes, and no oxygen.

What was the Archaean eon?

Started after the Hadean 3.5 bya and ended about 2.5 bya. The first prokaryotic cells came to life in this period, including cyanobacteria that would produce O2 as a byproduct.

What was the great oxygenation event? Why was it important for Eukaryotes and multicellular life?

Photosynthetic life like cyanobacteria were very successful, using the CO2 in the atmosphere and turning it into O2. Many cyanobacteria die (which later became crude oil). Using oxygen would later be advantageous for the electron transport chain, allowing eukaryotes to make more ATP. More energy allowed for more reproduction thus rapid evolution and diversification of life.

What was the Proterozoic eon?

The Proterozoic eon began 2.5 bya and ended 543 mya. Eukaryotes rose during this eon, and then multicellular organisms. Life began to diversify rapidly from the use of oxygen produced by cyannobacteria. The first plants emerged from ancestral green algae in the middle Proterozoic. Fungi and Animals branched from a common ancestor in the late Proterozoic.

What are the eras of the Phanerozoic eon?

Paleozoic, Mesozoic, and Cenozoic.