The Origins and evolution of life

Transcription

1 The Origins and evolution of life

2 The Origins and evolution of life Geologic time scale The geologic time scale provides a system of chronologic measurement used by geologists, paleontologists and other earth scientists to describe the timing and relationships between events that have occurred during the history of the Earth. The largest defined unit of time is the supereon, composed of eons. Eons are divided into eras, which are in turn divided into, epochs and ages. Units in geochronology Periods of time Eon Era Epoch Age Description > Half a billion years (4 in total) Hundred million years (12 total) Tens of millions of years Millions of years

3 The Origins and evolution of life Geologic time scale The geologic time scale provides a system of chronologic measurement used by geologists, paleontologists and other earth scientists to describe the timing and relationships between events that have occurred during the history of the Earth. The largest defined unit of time is the supereon, composed of eons. Eons are divided into eras, which are in turn divided into, epochs and ages. This clock representation shows some of the major units of geological time Earth history. The Hadean eon represents the time before fossil record of life on Earth. Other subdivisions reflect the evolution of life; the Archean and Proterozoic are both eons, the Palaeozoic, Mesozoic and Cenozoic are eras of the Phanerozoic eon.

4 The Origins and evolution of life

5 The history of the Earth describes the most important events in the development of the planet Earth from its formation 4.6 ba to present

6 Hadean period 4.55 Billions years ago Hadean Eon (from Greek Hades= God of the Underworld) The Earth is forming by accretion of melted material ejected from a supernova shortly after the Big Bang The Proto-Earth grew by accretion of these material. The inner part of the protoplanet was hot enough to melt heavy metals that began to sink to the Earth's core. This so called iron catastrophe resulted in the separation of a primitive mantle and a metallic core, producing the layered structure of Earth.

7 Hadean period 4.53 Billions years ago The Giant Impact Hypothesis The Proto-Earth is impacted by a smaller planet. This impact ejected part of the crust into the space and created the Moon The giant impact hypothesis proposes that the Moon was created out of the debris left over from a collision between the young Earth and a planet. Evidences for this hypothesis include Moon samples which indicate that: 1- the surface of the Moon was once molten 2- the Moon has a relatively small iron core and a lower density than the Earth 3- similar collisions in other star systems happen. The colliding body is called Theia for the mythical Greek Titan who was the mother of Selene, the goddess of the moon The impact is thought to have changed the axis rotation of the Earth forever.

8 Hadean period 4.1 Billions years ago The Late Heavy Bombardment A period of intense meteorite s impacts

9 Archaean period 4 Billions years ago At the beginning of the Archaean (from Greek Arcké= Origins ), the Earth started to cool down. During the accretion of the protoplanet, a cloud of gaseous silica must have surrounded the Earth, to condense as solid rocks on the surface. An external layer of light elements, mostly H and He, surrounded the protoplanet forming an early light atmosphere, but the solar winds and meteorites would have driven off this atmosphere

10 Archaean period 4 Billions years ago A new Atmosphere now is needed, but the ingredients are inside the Earth. The Planet has to pull it out. By the beginning of the Archaean It would have been impossible for life forms to exist due to the composition of the atmosphere, which lacked oxygen and an ozone layer. Nevertheless it is believed that primordial life began to evolve by the early Archaean, with some possible fossil dated to around 3.5 Mya. Some researchers, even theorize that life could have begun during the early Hadean, surviving the possible Late Heavy Bombardment period in hydrothermal vents below the Earth's surface

11 Archaean period 4 Billions years ago During the early Archaean the mantle was still much hotter than today. Steam escaped from the crust, and more gases (CO2, CH4) were released by volcanoes, completing the second atmosphere.

12 Archaean period 4 Billions years ago

13 Archaean period 4 Billions years ago As the planet cooled down, clouds formed and it rained for ages. The new atmosphere probably contained H2O, CO2, N2, and smaller amounts of other gases. Significant amounts of greenhouse gas in the atmosphere prevented the surface water from freezing.

14 Archaean period 4 Billions years ago But the large amount of water of the Earth can never have been produced by volcanism and precipitation alone. Probably the rest of the water derived from the outer space

15 Archaean period 4 Billions years ago

16 Archaean period 4 Billions years ago The huge impact released an enormous amount of water all over the Earth s surface, creating the rest of the oceans

17 Archaean period 4 Billions years ago Now on the Earth there are all necessary conditions for the origins of life

18 Archaean period 4 Billions years ago In the early Earth, it is possible that some molecules started to aggregate.

19 Archaean period 4 Billions years ago Some of those molecules gained the ability to make copies of itself...it was the first REPLICATOR The high energy from volcanoes, lightning, and ultraviolet radiation could help drive chemical reactions producing more complex molecules from simple compounds such as methane and ammonia.

20 Archaean period 4 Billions years ago In the energetic chemistry of early Earth a replicator promoted the chemical reactions which produced a copy of itself. The replication was not always accurate: some copies were slightly different from their parent. From single molecules, the first replicators developed into more complex organic compounds including proteins, amino acids and nucleobases.

21 Archaean period 4 Billions years ago The era of DNA has begun All known life uses DNA as replicator

22 Archaean period 4 Billions years ago The prevailing theory is that a membrane formed after the replicator, which perhaps was RNA. Suddenly, some molecules of RNA started to close in proteic bubbles to protect from the difficult environment. The first cell was forming This LUCA cell (last universal common ancestor) is the ancestor of all life on Earth today and lived during the early Archean eon roughly 3.5 Mya. It was probably a prokaryote, possessing a cell membrane and probably ribosomes, but lacking a nucleus or organelles such as mitochondria or chloroplasts.

23 Proterozoic period 2.5 Billions years ago Proterozoic Eon (from Greek proté= before and zoe= life ) The land is now separated by the Panthalassic oceans and the continents start to move. PLATE TECTONICS takes place for the first time

24 Proterozoic period 2.5 Billions years ago From prokaryotic to eukaryotic cells

25 Proterozoic period 2.5 Billions years ago The first eukaryotic cells were heterotrophs, using other organic molecules as food.

26 Proterozoic period 2.5 Billions years ago Some unicellular prokaryotic and eukaryotic cells started to use CO2 and H2O to produce organic molecules with the energy of sunlight. Those eukaryotic organisms were the first protists.

27 Proterozoic period 2.5 Billions years ago That was the first photosynthesis Oxygen started to appear on the Earth s surface and the third Atmosphere formed Stromatolites are the oldest fossils of oxygen-producing organisms

28 Proterozoic period 2.5 Billions years ago The oxygen revolution Some of the oxygen (O2) was stimulated by the incoming UV radiation to form Ozone (O3). The Ozone layer now absorbs the dangerous UV radiation that before passed through the atmosphere. It allowed cells to colonize the surface of the ocean and, eventually, the emerged lands.

29 Proterozoic period 2.5 Billions years ago The photosynthesis revolution The photosynthesis created a new atmosphere, with always higher content of O2 and O3. Without the Ozone layer, UV radiation bombarding land and sea would have caused unsustainable levels of mutation in exposed cells. LAND IS ALMOST READY TO BE COLONIZED

30 Proterozoic period 2.5 Billions years ago The oxygen revolution

31 The Origins and evolution of life 4500 Ma: First Atmosphere (H and He) 4400 Ma: Second Atmosphere (H2O, CO2, N) From Greek Hades="Underworld" First Continental Crust 4200 Ma: Primordial Oceans From Greek Prote="before" and Zoe= Life From Greek Arché="Beginning"

32 Proterozoic period 2.5 Billions years ago Snowball Earths An ice age around 2.3 Mya could have been caused by the increased oxygen concentration in the atmosphere, which caused the decrease of (CH4). Methane is a strong greenhouse gas, but the concentration of methane could have decreased dramatically, enough to counter the effect of the increasing heat flow from the Sun. The Proterozoic saw then a couple of severe ice ages called snowball Earths

33 Proterozoic period 2.5 Billions years ago Around 1 billion years ago the first colonies of unicellular organisms evolved, they were the first sponges, bryozoa, primordial corals. Gradually differentiation of labors began to take place, for example some peripheral cells assumed different roles (protection) from interior cells (digestion, photosynthesis)

34 Proterozoic period 1 Billion years ago The continents come together and break-up several times. 1 billion years ago the continental masses were united in the Rodinia supercontinent

35 Proterozoic period 1 Billion years ago Suddenly the amount of CO2 in the atmosphere decreased. Because CO2 is an important green house gas, the climate of the planet cooled down. This PERIOD is known as second SNOWBALL EARTH Testo

36 Phanerozoic period 542 million years ago Phanerozoic Eon (from Greek fanerò = visible and zoe= animal ) The Phanerozoic Eon is divided into 3 ERAS Paleozoic Mesozoic Cenozoic today Life colonizes the land. First plants and then the first animals. Life usually evolves slowly. Sometimes there are explosions of evolution caused by changes of the environment (volcanic eruptions, meteorites, climate changes.

37 Phanerozoic period million years ago The Paleozoic Era Life evolution accelerated. Development of hard parts of the body, such as shells and skeletons in animals like mollusks, echinoderms, crinoids and arthropods.

38 Phanerozoic period million years ago The Paleozoic Era The hard skeleton and shells made the fossilization of such forms easier than those of their ancestors. For this reason much more is known about this period

39 Phanerozoic period million years ago The Paleozoic Era During this period the first vertebrates animals, as fishes, had appeared (Pikaia). It had a primitive vertebral column. It was our ancestor.

40 Phanerozoic period million years ago The Paleozoic Era Than the first fishes with jaws evolved (as the titanic 7 mt long Dunkleosteus)

41 Phanerozoic period million years ago The Paleozoic Era The conquest of the land O2 accumulated into the atmosphere is now ready to host multicellular organisms. Several hundreds million years ago, algae and fungi started growing at the edges of the water.

42 Phanerozoic period million years ago The Paleozoic Era The conquest of the land The time of the first animals to leave the ocean is still unknown, but probably they were some tetrapods becoming better adapted due to the presence of food (fungi and algae). The first tetrapods evolved from fish. It is thought that fins evolved into limbs allowing those animals to walk out of the water.

43 Phanerozoic period million years ago The Paleozoic Era The conquest of the land Later they may have ventured on land for brief periods. Some of them became so well adapted to terrestrial life that they spent their adult lives on land, although they hatched in the water and returned to lay their eggs. This was the origin of the amphibians

44 Phanerozoic period million years ago The Paleozoic Era The conquest of the land Plants evolved seeds, which accelerated their spread on land (by approximately 360 Ma)

45 Phanerozoic period million years ago The Paleozoic Era The conquest of the land The amniotic egg evolved, which could be laid on land, giving a survival advantage to embryos. This saw the divergence of the mammals, birds and reptiles from amphibians

46 Phanerozoic period million years ago Pangaea formed 300 Ma...the last supercontinent

47 Phanerozoic period million years ago The Mesozoic Era

48 Phanerozoic period million years ago The Mesozoic Era The most severe extinction event took place 250 Ma, at the beginning of the Mesozoic era (meaning middle life ). This extinction was possibly caused by a volcanic event, an asteroid impact, sea level fluctuations, or some combination of those factors. After this extinction event, some species survived and separated from reptiles

49 Phanerozoic period million years ago The Mesozoic Era

50 Phanerozoic period million years ago The Mesozoic Era Dinosaurs soon became dominant among the vertebrates. Existing mammals were probably all small animals

51 Phanerozoic period million years ago The Mesozoic Era By 180 Ma, Pangaea broke up into Laurasia and Gondwana Flowers evolved 132 Ma Competition with smaller birds drove many pterosaurs to extinction

52 Phanerozoic period million years ago The Mesozoic Era 65 Ma, a 10 km meteorite struck Earth just off the Yucatán Peninsula (Mexico). This ejected vast quantities of particulate matter and vapor into the air that occluded sunlight, inhibiting photosynthesis. Most large animals extinct marking the end of the Mesozoic era

53 Phanerozoic period million years ago The Mesozoic Era

54 Phanerozoic period million years ago The Mesozoic Era Mammals grew larger and became the dominant vertebrates. Perhaps around 63 Ma, the last common ancestor of primates lived. Some terrestrial mammals had returned to the oceans to become animals such as Basilosaurus which eventually led to dolphins and baleen whales

55 Phanerozoic period 65 million years ago On the land the primates era starts

56 Primates Prosimians Anthropoids Old World Monkeys Great Apes Hominids