Exploring Early Life and Its Patterns

1. Chapter 9 Early Life and Its Patterns • The oldest known fossils consist of filaments of • cyanobacteria (blue green algae) in rocks about 3.5 billion • years old. Fig. 9.1 • Because the heavy meteorite bombardment of the earth • did not cease until 3.8 billions years ago, life must have • originated in less than 300 million years early in the • plant’s history. • Because the simple early fossils do not preserve details • of biochemistry, we must simulate the origin of the life • through laboratory experiments. Forty years of laboratory • work have shown that most basic chemicals of life and • even simple cells with many of the properties of life can • arise by natural processes.

2. Fig. 9.1: Algal stromatolites exposed at low tide in Shrank Bay, Australia. Scale is one meter long. These concentrically layered, domed structures are formed when cyanobacteria trap sediment with their mucous coating, then grow upward through the sediment layer each day. Today large stromatolites are a very unusual occurrence, because most are heavily grazed by a variety of invertebrates. This sence must have been typical for over 3 billion years because stromatolites are the only common megascopic fossils known from rocks over 3.6 b.y. old until the early Cambrian.

3. 9.1 The Origin of Life • 1. Spontaneous generation • Prior to the microscope, people confused reproduction • with the actual origin of life. During middle ages, many • scholars were preoccupied with the idea of Spontaneous Generation, believing that putrefaction somehow produced metamorphosis of nonliving to living matter. • The spontaneous generation mean that life arise from • non-life in the beginning, but why it does not arise from • non-life today?? • The believer of this idea was argued that; spontaneous • generation does not occur under present earth conditions • because the earth’s modern atmosphere is too corrosive • and too oxidizing to allow it. • The early atmosphere had almost no free molecular • oxygen and was rich in the right kinds of chemicals to • produce life.

4. 2. The Warm little Pond or Physical condition. • Darwin suggested that ‘ insome warm little pond, with all • sorts of ammonia and phosphoric salts, light, heat, • electricity, a protein compound was chemically formed, • ready to undergo still more complex changes’. • Oparin & Haldane 1920, follwed Darwin’s idea, they • proposed that an earth with a reducing atmosphere and • abundant methane CH4 and ammonia NH3 would have • been the ideal soup for the origin of life. • The simplest building blocks of life, such as amino acids • (which are linked to form proteins), sugars, and fatty • acids (which linked to form complex fats, or lipids) can • easily be produced in laboratory experiments that • simulate the original conditions of the early earth. Other • experiments show that droplets of proteins can • condense, surrounded by a lipid membrane, to form • proteinoids with very lifelike properties.

5. Carl Woese 1984 has studied the genes of a number of types of bacteria and finds two types came from the universal ancestors:- • Archaebacteria: a bacteria kingdom live on hydrogen sulfide, on methane, or in extremely hot salty springs. • Eubacteria or true bacteria, including most familiar bacteria, plus cyanobacteria. Fig. 9.6 • 9.2 The Record of early life Before the Paleozoic • Earliest life in the form of single-celled autotrophic cyanobacteria (blue-green algae) is found in some of the oldest rocks known in northwestern Australia, dated at about 3.5 billion years. • From most of the Cryptozoic, until about 650 million years ago, only single-celled or filamentous cyanobacteria are known. They occur in structures called Stromatolites.

6. Fig. 9.6 Family tree of life based on molecular similarities of RNA.

7. Fig. 9.8 F • one of the oldest known stromatolites , from the 3.4 b.y. old beds in the swaziland super group of South Africa. • They are the only megascopic fossils in rocks from 3.5 billion to 700 million years in age. • They found in Warrawoona Group in north west Australia and in the Fig Tree Groups in South Africa.

8. Fig. 8.9 G Modern filamentous cyanobacterium whose cell are identical in size and shape to the cyanobacterial fossils from western Australia.

9. Fig. 8.9.H A four-celled colonial cyanobacterium surrounded by thick sheath, from cherts in the Ural Mountains about 1.55 b.y. in age.

10. Fig. 9.8 I Living Gloecapsa, a cyanobacterium identical in size and shape to the four-celled fossil.

11. Fig. 9.8 K : Living colonial cyanobacterium .

13. The first cells were prokaryotes- they had neither an • organized nucleus nor organelles ( sub-cellular • structures) and reproduced by simple cell division. • The first eukaryotes- cell with an organized nucleus and • organelles appeared in the late Precambrian. • Multicellular animals (metazoans) are known first as • trace fossils, usually either tracks or trials of wormlike • creatures. • Ediacaran fossils are the earliest animal fossils. They are • apparently not related to later groups found in the • Paleozoic. Fig. 9.11.

14. B C A Fig. 9.11:some of the complex Ediacaran metazoan fossils from the Ediacara Hills, South Australia. A: a segmented, wormlike creature that reached almost a meter in length. B: more elongated worm like form. C: a strange form that has been linked to arthropods .

15. 9.3 Metazoans, Vendozoans, and the Cambrian explosion The sudden appearance of species belonging to several of the main divisions of the animal kingdom in the lowest known fossiliferous rocks, namely those of the Cambrian was great problem for Darwin in 1859 and other scientists. Simply the problem was the appearance of richly fossiliferous Cambrian strata full of trilobites were underlain by seemingly barren Precambrian rocks!!! Based on this notes many question was raised, such as Did life originate abruptly, or was there hidden somewhere an undiscovered fossil record of the transition to multi-cellular life? Many scientists shared to answer this question:- 1. Stanley Tyler in 1950 found the microfossils from 2 billion years old rocks. After this discovery, Barghoorn, Schopf and many others has documented hundreds of microfossil localities and has shown that single-celled organisms dominated the earth from 3.5 billion years ago until about 600 million years ago.

16. 2. In 1946 Reg Sprigg found impressions of “jellyfish” in the Rawnsley Quartzite in the Ediacara Hills of South Australia. Fig. 9.11. After decades of Sprigg’s discovery Australian paleontologists collect more of these fossils until there was clear evidence of a diverse assemblage of soft bodied animals that predated the Cambrian. These specimens are all impressions of soft bodied animals preserved in a shallow – marine sandstone, they are often difficult to interpret, but there is no question that they represent multicellular animals, or Metazoans . These fossils are known as the ‘Ediacaran fossils’ and found later in many places over the world such as England, China, Siberia, Scandinavia and Russia….and so on, therefore, it became a reality that these fossils are dominated the world in the interval of time now called theVendian. 600 – 544 M.Y Many Vendian fossils vaguely resemble jellyfish, sea pens and wormlike animals, but many more are clearly unrelated to anything living today. So they called Vendozoa.

17. 9.3.1 Cambrian Explosion of Shelly Invertebrates • For times earlier than 600 m.ys. ago, the fossil record • yields only stromatolites and microfossils, such as • acritarchs, which declined about 675 m.y. ago. • From 600 to about 550 m.y. ago, the world was dominated • by the Ediacaran soft bodied forms. Except for some • tiny, tube-shaped fossils made of calcite, there are no • other animals preserved, Fig. 9.13 and 9.14. • Early in the Cambrian Period, Vendian animals • disappeared completely and were replaced by little • shelly fossils (fig. 9.14). These tiny shells were the • harbingers of the abundant shelled invertebrates found • later in the Cambrian. • In addition to the small shellies earliest Cambrian strata • yield burrowing or trace fossils in the sediments; which • mean that complex worms, tube like bodies capable of • burrowing must have been present.

18. Fig.9.13 Fossils from the lowest Cambrian Tommotlanstage are mostly microscopic phosphatic tubes, caps, and spicules from tiny animals, which were just beginning to form skeletons. All scale bars are 1 mm. specimens are from south Australia and China.

19. Fig. 9.14 Vendian and lower Cambrian strata documented the transition from the simplest soft bodied metazoans to complex skeletonized invertebrates.

20. After this information, there is a logic questions, that • What triggered the replacement of microfossils with large soft-bodied animals in the Vendian??? • Why were the latter (the soft-bodied animals) replaced by shelly fossils in the Cambrian ????? • There are several hypotheses competing, but some points seem clear: • The extinction of the late Proterozoic acritarchs seems to correlate with a gigantic glacial event about 600 m. y. ago, were the earth close to complete refrigeration, therefore late Proterozoic microorganisms were nearly wiped out and never completely recovered after glaciers retreated. • Vendian oxygen level was estimated to reach 6-10 percent, this percent was too scarce for large animals to function, so limited oxygen was the critical factor preventing the evolution of multicellular life for almost 3 billion years.

21. 3. The latest Proterozoic was an episode of tectonic change; rifting and volcanic activity produced a worldwide transgression which expanded the area of shallow marine shelf available for life. Also rifting and volcanic activity may have released many of nutrients and carbon into shallow-marine environment, where shell-building organisms could use them. All above reasons caused explosive growth of organisms near Vendian-Cambrian boundary. 4. Increased nutrients provide materials for animals to build hard shells, mostly calcite. The hard shell used by animals for protection from predators and competitors. As a fact that living organisms cannot secrete calcium carbonate until the atmospheric oxygen level reaches a critical threshold; this explain why earliest shelly fossils are mostly calcite or phosphatic tubes, meanwhile, the oxygen reached modern level in late Cambrian, great number of hard CaCO3 shelled organisms start toappear.

22. 5. The shallow marine world was once covered with thick • cyanobacterial mats, but in the early Cambrian they • nearly disappeared. • Based on this note:- • The appearance of the small shelly fossils and deep • burrows are correlated with this decline in stromatolites • which formed by cyanobacteria. • So, is this was an accident ??? • The answer :- • Before the appearance of small invertebrate animals, • nothing fed on cyanobacterial mats. • - Some of these small shelly fossils must have been • primitive molluscus that grazed and cropped • stromatolites. • Once these shelly animals evolved, they would have a • virtually unlimited food source and could easily cut the • cyanobacterial mats and domes to pieces.

23. The believer of this idea reasoned that, by the recent distribution of stromatolites, while stromatolites survive today only in environments that are hostile to grazing invertebrates. • Therefore, stromatolites found today in lagoons environment which is too salty for grazing snails to live in. • Also the same case in shallow channels in the Bahamas where currents are too strong for clinging invertebrates. • 6. Diversification of invertebrates led to even more • complex ecological relationships, such as predation. • By the middle Cambrian time, there is evidence of large • predators, which reached half a meter in length, as well • as trilobites with healed bite marks, in the other hand, • many Cambrian animals have spiky or platy armor as • devices to thwart the predators. • the appearance of predators represents a more complex food chain as well as from producer (plants) to feeder.

24. Cambrian fauna • Arthropods: • this is the jointed legged phylum of animals that also includes insects, spiders, scorpion, crabs, many other kinds of animals. • The most famous fossils from this phylum are the trilobites, (Fig. 9.16) these fossils was well preserved due to the skeleton composition, which consists of both calcite and organic chitin. • Modern arthropods skeletons composed of only chitin, that’s why its not found as fossils . • In Cambrian seas the trilobites evolved so rapidly around the world, therefore they used as tool of correlation. • More than 600 species are known from the Cambrian, but they ended by the Ordovician. • Trilobite burrows and feeding tracks are among the most common trace fossils of the Cambrian.

25. Fig. 9.16a Fig. 9.16 A Early Cambrian Trilobite Olenellus

26. Fig. 9.16. B Middle Cambrian Trilobite Ogygopsis

27. Fig. 9.16. C Middle Cambrian Trilobite Paradoxides

29. 2.Archaeocyathids: • a strange group of organisms shaped like double-walled • ice cream cones, Fig. 917A-I. • They are 25mm in diameter and up to 150 mm high, but • some large ones can reach one meter in length. • They are perforated by bores, they were probably filter- • feeders as sponges, some paleontologists think • archaeocythides are just aberrant sponges, other argue • that their anatomy is completely different from that of • modern sponges or any living group. • Because they are now extinct and we have no soft • tissues preserved, their relationships are controversial.

30. Fig 9.17 A-I Early Cambrian Archaeocyathids J-k inarticulate brachiopods L-O Archaic molluscus P An eocrinoid, true crinoids replaced them in the Ordovician. Fig. 9.17

31. 3. Brachiopods • These animals have two clam-like shells joined for • protection. • A long, fleshy stack called a pedicle extends through the • hing area and helps the animal burrow are attach to hard • surfaces. • The earliest Cambrian brachiopods known as inarticulate. • Most inarticulate brachiopods have shells of chitin and • phospate.

34. 4. Molluscs • Today they are represented by clams and snails , but • early Cambrian were much simpler. • By the middle Cambrian, true snails and clams had • evolved, but they remained rare until the Ordovician.

35. 5. Echinoderms or • spiny skinned • animals. • Today they are • represented by • starfish, crinoids • and cucumbers. • Most are built of • calcite plates. • All living • echinoderms are • built on a pattern of • five-fold symmetry, • such as the five • arms on starfish. • Cambrian • echinoderms have • no living • representatives. • See Fig 9.19.

36. Fig.9.19 • Heicoplacus, • it show no Similarity with • living ecinoderms. • It represents a primitive • type from the lower • Cambrian. • Based on its spiral • arrangement of plates, it • apparently transported • food up the spiraling • grooves by means of tube • feet. • Original specimen • approximately 10 cm3 long.

37. When the Cambrian fauna examine the following note will • be clear:- • Most of the animals were extremely primitive forms which did not survive, many of them represents an early stages of their phyla evolution. So, after each evolution stage the old stage pushed aside or extinct. • The ecological communities were very simple. • For example: • The stromatolite – cyanobacteria – archaeocyathid, included only a few burrowers, mostly worms and inarticulate brachiopods. • It seems from all the information which discussed till now about the Cambrian fauna, that the Cambrian life is simple and monotonous!! But the Burgess Shale fauna which discovered in the Rocky Mountains near Field, British Columbia showing that Cambrian world was much richer than what we imagined.

38. Cambrian life include:- • At least 20 types of Arthropods with body designs • fundamentally different from those of any living • arthropod. • - A number of wormlike animals. • At least fifteen other kinds of animals that cannot fit into • any living phylum of invertebrates. • Therefore each type of the above Cambrian organisms represents a different version of metazoan design that has not survived. • So, the Cambrian had diversity comparable to that of later periods, but with an important difference: almost all this diversity is in primitive forms, each of which would represent a different phylum or class in a modern classification. By contrast, from the Ordovician onward, most fossils fit into about eight phyla, and just a few classes and orders within these phyla account for most species.

39. Fig. 9.22a: Time line of the early evolution of life during the Cryptozoic and Cambrian

40. Fig. 9.22b: Continued.