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History of Life on Earth. Deep Time 4550 mya to present. eon. era. era. era. Precambrian Eon. Hadean Era Geology Birth of solar system - 4.55 bya Escaping gasses create early atmosphere Earth’s core forms - 4.4 bya Great oceans form Oldest known rocks - 4.055bya Biology
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History of Life on Earth Deep Time 4550 mya to present
eon era era era
Precambrian Eon • Hadean Era • Geology • Birth of solar system - 4.55 bya • Escaping gasses create early atmosphere • Earth’s core forms - 4.4 bya • Great oceans form • Oldest known rocks - 4.055bya • Biology • First evidence of life - 3.85 bya
Precambrian Eon • Archaean Era • Geology • Small continents form • Continents begin to shift • Biology • Bacteria diversify -3.85 bya • First photosynthetic bacteria – 3.7bya • Oldest fossils – 3.5 bya • First Eukaryotes – 2.7 bya • Bacteria on land – 2.6
Key Concepts Potential signs of life date to 3.85 bya but claim is controversial Earliest accepted fossils of bacteria date to 3.5 bya Microbes still constitute most of the earth’s biodiversity
Archaea 1st Mass Extinction
First photosynthetic bacteria • Early microbes thrived in an oxygen-free environment, feeding on organic molecules like glucose and produced energy by the process of fermentation. • As populations grew and food supplies became scarce, bacteria that could generate their own food and energy evolved. • Many of them used photosynthesis in which energy radiated from the sun is converted into chemical energy the organism can store and use. • Photosynthesizing bacteria grow larger and reproduce faster than their competitors.
Oxygen and diversity • As more and more cyanobacteria spread across Earth, the oxygen waste they produced through photosynthesis proved toxic to most other microbes. • In fact, only those sheltered in oxygen-poor habitats like the murky depths and those with genetic mutations that somehow enabled them to tolerate oxygen survived. • The alternating layers of rust-colored and gray deposits suggest oxygen production fluctuated over suggest oxygen production fluctuated over time.
Paleoproterozoic (2500 to 1600 mya) • Oxygen present in atmosphere so - • Metabolism began diversification • Earliest Proterozoic life was single-celled and anaerobic – did not use oxygen • Oxygen was toxic to these organisms – 1st max extinction event! • Various ways to breakdown glucose anaerobically • Later, more complex single-celled aerobic life evolved which used oxygen • Use oxygen for the process of respiration
Paleoproterozoic • Peak of stromatolites • Cyanobacteria oxygenated the atmosphere • Oxygen caused “Rusting of the Earth” • Depletion of oceanic iron • Combined with oxygen and precipitated as “rust” • Precipitated iron settled to the ocean floor • Iron found in Banded Iron Formations
Earliest signs of life • Oldest evidence of life dates to 3.7 bya • Carbon contained in rocks • Claim is controversial • Oldest stromatolite (bacteria) fossils date to 3.45 bya Top: Living stromatolites Bottom: Fossil stromatolites
Oldest Fossils • Look like cyanobacteria suggesting ancient origin for photosynthesis • Cyanobacteria fossils from stromatolites date to 2.8 to 3.45 bya • Filamentous strands of cells resembling modern species of Oscillatoria or Lyngbya • Stromatolites still exist as living fossils
Stromatolites • Layered mounds of calcareous material between cyanobacterial cells. • Following slides show fossil stromatolites • Closest place to find these: Upper Peninsula of Michigan
Doing the backstroke among the stromatolites in a tropical Precambrian sea in Michigan
Kona Dolomite from Michigan dated to over 2 billion years old. Thought to be astromatolite.
Stromatolite Formation • Many layers were produced as calcium carbonate precipitated over the growing mat of bacterial filaments. • Photosynthesis by the cyanobacteria depleted carbon dioxide in the surrounding water, initiating precipitation of calcium carbonate. • The minerals, along with grains of sediment precipitating from the water, were then trapped within the sticky layer of mucilage that surrounds the cyanobacterial colonies, which then continued to grow upwards through the sediment to form a new layer.
Stromatolite Formation • As this process occured over and over again, the layers of sediment were created.
Stromatolite formation still occurs today; Shark Bay in western Australia is well known for the stromatolite "turfs" rising along its beaches. • Shallow, marine, low latitude, hypersaline environments. Also found in the Bahamas.
Oxygen and diversity • As more and more cyanobacteria spread across Earth, the oxygen waste they produced through photosynthesis proved toxic to most other microbes. • In fact, only those sheltered in oxygen-poor habitats like the murky depths and those with genetic mutations that somehow enabled them to tolerate oxygen survived. • The alternating layers of rust-colored and gray deposits suggest oxygen production fluctuated over suggest oxygen production fluctuated over time.
Paleoproterozoic (2500 to 1600 mya) • Oxygen present in atmosphere so - • Metabolism began diversification • Earliest Proterozoic life was single-celled and anaerobic – did not use oxygen • Oxygen was toxic to these organisms – 1st max extinction event! • Various ways to breakdown glucose anaerobically • Later, more complex single-celled aerobic life evolved which used oxygen • Use oxygen for the process of respiration
Paleoproterozoic • Peak of stromatolites • Cyanobacteria oxygenated the atmosphere • Oxygen caused “Rusting of the Earth” • Depletion of oceanic iron • Combined with oxygen and precipitated as “rust” • Precipitated iron settled to the ocean floor • Iron found in Banded Iron Formations
Banded Iron Formations • Banded Iron Formations (BIFs) are another type of stromatolite • 1.8 to 2.5 billion years old • Composed of alternating layers of iron-rich material (commonly magnetite) and silica (chert) • Also found in Northern Michigan • How they were made • Cyanobacteria provided the source of oxygen for BIF formation.
Banded Iron Formations • How they were made #1 • Large amounts of the soluble form of iron were released from the Earth's interior into the Archaean oceans. (reduced ferric iron) • Oxygen in the oceans would have oxidized (rusted) this iron to form insoluble (ferrous) iron oxide which precipitated and formed layers of reddish sediment on the ocean floor. • The layers or banding is assumed to result from cyclic peaks in oxygen production. It is unclear whether these were seasonal or followed some other cycle.
Banded Iron-Formation • Seasonal and/or biological cycles resulted in intervening periods when iron or oxygen were not as available • The black layers are made of chert (micro-crystalline quartz) that was laid down during these intervening periods.
Banded Iron Formations • How they were made #2 • It is also thought that bacteria may have played a role in the formation of these bands of precipitated iron. • Certain bacteria can oxidize reduced ferric iron to insoluble ferrous iron
Banded Iron Formations • Economic significance • BIF’s are important sources of iron ore (mining) • Bacteria can precipitate a number of other minerals including manganese and even gold • These processes are being adapted to facilitate mining of these minerals and removal of heavy metal pollutants from soils
Key Concepts Potential signs of life date to 3.7 bya but claim is controversial Earliest accepted fossils of bacteria date to 3.45 bya Microbes still constitute most of the earth’s biodiversity
