Known from dates on meteorites (Carbonaceous chondrites) suggests condensation of the protoplanetary disc of dust ~4.5562±2 Ga suggesting a minimum solar system age of 4.5695±2 Ga (Baker 2005)
Zircons surviving from this period show that continental crust had formed and there was a water ocean by 4.4 Ga.
The other problem is the “Heavy Bombardment” with potentially Earth sterilizing impacts until ~3.8 Ga (Schopf 2002). Hyperthermophiles would do well here if large areas of the ocean were turned to near steam by big impacts.
Sedimentary Uraninite (UO2), siderite (FeCO3) and pyrite (FeS2) pebbles found unoxidized in sediments older than 2.3 to 2.6 Ga but none afterward; pebbles of pyrite do not occur today in stream gravels. Indeed, today sulfide ores can “melt” in open air creating sulfuric acid and eating holes in things—like the desk in my office!
Banded Iron Formations (BIFs) common between 2-2.5 Ga,--
Contain ~90% of world’s iron supply
Fe+2 is soluble in seawater but when oxidized to Fe+3 becomes insoluble.
Possibly ppt in waves by cyanobacterial production of O2—would account for the ‘varve-like’ nature of some BIFs
BUT the deep oceans seem not to have become oxic until later, since have large BIFs until ~1.8 Ga [Canfield 1998]; (indeed, rare BIFs at ~700-800 Ma)
The dates of the first red beds are not known exactly –the soils are cut by intrusive dikes and sills with 2.2, 2.1 and 2.06 Ga dates, so they must be somewhat older than 2.2 Ga
The widespread development of lichens and terrestrial vegetation (but not higher land plants) by ~800-700 Ma; the addition of organic matter to terrestrial soils was critical for the production of clay (by chemical weathering). Before this time, there was little clay on land or in the ocean.
Last BIFs associated with an interval ~600-750 Ma associated with repeated phases of the “Snowball Earth”.
”Snowball” is the theory that the Earth froze completely over. Evidence:
glacial deposits that are found near the equator (and near sea level),
anoxia in the deep sea (suggestive of low turnover of the ocean, and
“Cap carbonates”—massive deposits of microbial carbonates that the hypothesis suggests were rapidly ppt when the Earth was unfrozen and CO2 stored in the ocean was released into the ATM.
The development of forests ~350 Ma; The burial of lignin and woody plant material drew down atmospheric CO2 concentrations creating a major glaciation and creating the first coal deposits; before this we did not have coal.
graphite crystals and graphite inclusions. δ13C = -40‰ which is difficult to achieve without life [Indeed, such negative ratios are commonly associated with methanogenesis, suggesting this biochemical pathway existed at the dawn of life. metosomatic (hydrothermal-metamorphic) in origin, not sedimentary, and suggesting that the negative δ13C could be produced by breakdown of carbonate rocks at high temperature metamorphism
Furnes et al. 2004, Science: Microbial borings in 3.48 Ga pillow basalt glass rims from Barberton, S. Africa. Furnes et al.  report trace fossils and δ13C values (to -16‰) in pillow basalts dated at 3482 Ma (zircon age) and 3486 Ma (Metamorphic age) and age on cherts overlying the lavas (3472 Ma)
The borings are suggestive of thermophillic (>70°C) life in hydrothermal systems. The nature of these organisms has not been determined, but similar traces are found in modern basalts to a depth of several 100 m depth in basalt sequences
S isotope evidence for sulfate reduction in 3.47 Ga Australian rocks
Original claim: Filaments preserved in the 3.465 Ga Apex Chert in Western Australia (e.g. Schopf et al. 2002). Schopf et al have argued that the fossils are made of kerogen (refractory organic material) and are similar to filaments in younger Precambrian rocks.
filaments show structures similar to cyanobacterial structures including possible segmentation
sizes similar as well.
The biological nature of these fossils has been questioned (see Braisier et al 2002) on the grounds that they:
occur in a hydrothermal chert deposit, not sedimentary rocks
occur as isolated strands, not mats
are composed of graphite with similar composition to small flecks and spheroids in the same rocks
are found in both clasts and vein-filling material in the cherts.
Knoll seems to agree that these are not definitely biogenic.
3.465 Ga Stromatolites from Strelley Pool Chert, Pilbara, Australia: laminated sediments have been described as stromatolites created by consortia of prokaryotic bacteria, but these have also been disputed on the grounds that such structures can form inorganically.
For example: Lowe (1994) Geology argues that these stromatolites are inorganic because they are rare, have no sediment between the mounds, have uniform laminae thickness, are associated with evaporates, and show, in one case, evidence of mechanical folding.
Others have re-examined the area and found more stromatolites: the “new” stromatolites have features (several orders of contorted laminae, kerogen-rich laminae, and lenses of desiccated fragments, filling troughs between mounds) that are unlikely to reflect hydrothermal activity or deformational features (Buick 2001).
BUT nobody has reported filaments from these structures.
Allwood et al. (2006) note also that these stromatolites show:
diversity of shapes from conical to mound-like, cuspate and “egg carton” forms
evidence of being soft (and therefore not abiotic crusts)
morphological diversity distinctive of different depositional environments.
methane in fluid inclusions in chert by 3.46Ga suggesting antiquity for Archaea
Buck Reef Chert, South Africa (Tice and Lowe, 2004, Nature): 3416 Ma, Laminations, stromatolites, and carbonaceous matter in shallow water sediments with δ13C = -20 to -35‰, but no body fossils. Possible methanogens and probable plankton.
Carbon isotopes show period (2.8-2.3 Ga) when organic C dominated by methanogenesis—suggests little O2 around to oxidize methane before ~2.3 Ga; eventual loss of CH4 in ATM is possible trigger for the Paleoproterozoic glaciation.
The presence of long chain steranes (and cholesterols) by 2.75 Ga indicates the presence of eukaryotes about 500 million to 1 billion years before the body fossil record shows their presence (Brocks et al. 1999)
These Eukarya might not be full blown eukaryotes however, but may have been just nuculate forms without mitochondria or chloroplasts.
Tumbiana Formation, Australia (Buick, 1992): 2720 Ma, stromatolites, in lake sediments; must have used oxygenic photosynthesis since there was no sulfate around (being fresh water) and there was little H2 around (since the lakes are calcitic not siderite) to permit anoxygenic photosynthesis to occur. More isotopic evidence for methanogens.
Methanogens turn up as distinct lipid biomarkers by 2.7 Ga
Marra Mamba Formation, Jareenha formation, Australia (Brocks et al. 1999, Science): 2600-2690 Ma: Biomarkers of cyanobacteria (2-methylhopanes) and eukaryotes (28C and 30C steranes)
stromatolites become diverse and common after 2.5 Ga, suggesting diversification associated with oxygenic photosynthesis and perhaps with eukaryotic communities.
1.85 Ga: Grypania—macroscopic ‘comma’ or spiral-shaped organic compression fossils from Montana (1420 Ma), China (1850 Ma) up to 13 mm long and 2 mm wide.
~1.8 Ga have first Acritarchs—simple, often large, crushed bags with a split in them that could be eukaryotes but could be prokaryotes too
Get excellent preservation of cyanobacteria.
The reason this is important is because it proves small little dinky things CAN be preserved. But there are no blade-like algae, no testate (shelled) aeomebas.
Instead, get large, compressed spheres. These spheres tend to be big but unexceptional in terms of ornamentation- see plate 6 in Knoll.
Also something called Tappania- Plate 6E. Very clearly eukaryote with processes on the outside of a vegetative-like cell wall.
In addition, in scattered places all around the world, there are large helical impressions, >5cm wide and also strings of beads
Nobody really knows what they are, but they are definitely biological and have to be eukaryotes.
1.2 Ga: Sommerset Island cherts- up in Artic Canada- clear red algal filaments. This tells us that reds and greens separated from each other more than 1.2 Ga.
Lakhonda Formation, Siberia: Simple branching filaments of Heterokont algae. Heterokonts are algae (like Kelp, datoms) that have motile reproductive stages with two types of flagella. In other words: a complex life cycle.
800-700 mya: Grand Canyon shales and also Spitzbergen- there are green algae, almost
able to identify to genus level. Green algae are a primary engulfing of a cyanobacterium unlike the multiple engulfing origins of red algae
Also vase-shaped testate ameobae.
635 mya- Doushantuo Formation in southern China.
Think about this one in terms of origin of animals- extraordinarily important deposit. Composed of shales, phosphates and carbonates.
Fossils are preserved in phosphatic minerals and has huge diversity of eukaryotic forms- see plate 5 and figures 9.2 and 9.3 But then some of these things went extinct.
And the coolest is the EMBRYOS. All over. Can see divisions.
There are small spheres with bumps and stuff, seaweeds, flanged tubes, multicellular red and green algae,
Animal eggs and embryos, Probably sponges.
Doushantou embryos are ~599 Ma
Fish first appear in the early Cambrian (~525 Ma) of China. These are chordates characterized by a notochord (a stiffened rod) a dorsal nerve cord, chevron folded muscles. The early chordates lacked jaws (they were “agnathans” “no jaws”) and bone and resemble modern “Amphioxis” [now called Branchiostoma].
[Interlude: Amphioxis song]
The conodonts appear in the early Cambrian ~525 Ma still lack bone but have
mineralized tooth-like elements arranged in 7 batteries of specialized structures.
Wear patterns suggest they were used as teeth rather than supporting a feeding structure and
they range from stabbing forms at the front of the mouth to crushing forms at the rear, further demonstrating their use as teeth;
However conodont animals had no jaws. Large eyes suggest these were visual predators. Conodonts were likely pelagic predators since they:
are very widespread (and used for biostratigraphy)
small (a few centimeters, max),
are found commonly in relatively deep ocean sediments
Bone, indicating the development of modern fishes (Craniates) appears in the early Cambrian (~525 Ma; again in the Chengjiang Lagerstätten) as ostracoderms—torpedo shaped bony-plate covered fishes without jaws.
518 Ma: Chengjiang Biota, China—has 170 species (and will likely increase in a few years). Most of major phyla are represented, but for some strange reason, Molluscs and Echinoderms are RARE. Dominated by Arthropods (>65% of specimens and >50% of species)
BUT, also a lot of “Lobopods” (like Microdictyon), sponges, worms, and fish.
510 Ma: Mass Extinction. Almost all of the trilobites that were alive from 530-510 Ma go extinct. That mass extinction of trilobites is what determines the stratigraphic limit of the Lower Cambrian.
507 ma ICONIC fossil deposit (most famous) BURGESS SHALE. This is EARLY MIDDLE CAMBRIAN. It is in northwestern Canada, Discovered by Wolcott. Then Simon Conway Morris came and got all the fossils and reanalyzed them. In the Burgess got basically all basic architecture of the animals- EXCEPT the bryozoans. Which is weird, because they are obviously missing.
The period of 530 MA-to-Burgess produces the radiation of animals with modern body plans.
It is the CROWN GROUP radiation in the Burgess as opposed to the STEM GROUP radiation with occurred in 543-530.
But, in early middle Cambrian, Burgess Shale, still have stem and crown taxa living together.
Even though organisms look really weird- we have predators, deposit feeders, filter feeders, swimming things, etc.
Bottom Line: here we have quite complex marine communities with all trophic levels, an ability to mine sediment (and recycle nutrients in the sediment), and ability to suspension feed near the sea floor. Also have reefs (made by archeocyathids). At least some critters were active predators and therefore highly mobile. These features are part of all modern marine ecosystems—the parts are all there ~30 million years after the base of the Cambrian.
The first jawed fishes are known from the late Ordovician (~470 Ma).
Jaws are believed to be derived from modified gill arches that were first used for respiration;
one hypothesis is that jaws evolved in fishes that were using the gill arches to forcefully suck in water.
Jaws then just carry the suction feeding to an extreme. [suction feeding involves the abrupt increase in the opening of the jaws, creating a pressure difference that sucks the food into the mouth.]
The jaws emerge from the enlargement of the inner gill arches and the hyoid bones emerge from a secondary gill arch behind the jaws.
Sharks appear about 420 Ma (Silurian [although there are probable Ordovician shark teeth]) and develop
many modern features including partly calcified cartilage,
a heterocercal tail (in which the notochord beds into the upper limb of the tail) and
two sets of pectoral and pelvic fins located under dorsal fins.
The sharks diversify still further in the Carboniferous although the main radiation of modern sharks is in the Jurassic and Cretaceous.
We think of sharks as big scary things, but sharks have a relatively low basal metabolic rate compared to later boney fishes and particularly compared to marine reptiles and mammals. Sharks, accordingly, do quite well in relatively low O2 Paleozoic oceans.
The ichthyosaurs are an early Triassic (~245-91 Ma) to late Cenomanian group, with most diversity in the Triassic and Jurassic.
The first marine turtles appear in the Aptian/Albian ~105 Ma and split off early into the green sea turtles and leatherback turtles
hippos (whales-E. Eocene ~55 Ma)
Fully pelagic whales evolve in the late Eocene (~34-36 Ma) with the split between the odontoceti (toothed whales) and the mysticeti (baleen whales). First mysticetes had “crab-eater” type teeth with numerous cusps. These were replaced by hairy panels (baleen plates) as a filtration device
minks (otters-Late Oligocene ~ 25 Ma), and
bears (seals-Oligocene ~30 Ma),
bears (polar bear-mid Pleistocene ~400,000 yrs)