>Top 10. Green Earth: The Rise of the Terrestrial Biosphere:
- Earth's Age: 4.0 to 4.5B years (the last 542M years)
- Plate tectonics saved Earth from itself.
- Continental masses shifted poleward, liberating the Equator from ice accumulating lands, moderating the extreme snowball-hothouse cycle.
- Abundant new photosynthetic algal life helped buffer the wild fluctuations of CO2.
- During 542Ma, continents have continued to shift, first closing one ocean to form yet another great supercontinent, then breaking up to form the still-widening Atlantic Ocean.
- Climate has fluctuated from hot to cold and back again many times, thought not to the snowball-hothouse extremes of Neoproterozoic.
- Exquisitely preserved fossils; teeth, shells, bones, and wood.
- Animals and plants turn out to be particularly sensitive to changes in Earth's environment.; Animals and plants respond to Earth's cycles quickly - they evolve fast or they die. As old species die out, new species take their places.
- Shifting continents of the past 550M years continued to provide changeable stage for evolution of Earth.
- >Top Act-1:
- The beginning of Cambrian Period (542Ma):
- Supercontinent of Rodinia broken into several large pieces.; Gondwana stretching from south pole to beyond the equator.
- Laurentia (including today North America, Greenland and much of Europe)
- Over the next 250M years, plates move northward. Laurentia by merging first with what would become Europe, then with a significant part of Siberia.
- >Top Act-2:
- 300Ma, northward tracking Gondwana collided with Laurentia to form the most recent supercontinent, Pangaea.; closing of the ancient sea between North America and Africa, a collision that birthed the Appalachian Mountains. (soared 9-10Km high)
- 3/4 of it located in the southern hemisphere.
- Superocean surrounded Pangaea was Panthalassa (<G. all sea)
- 175Ma, the opening of Atlantic Ocean.
- First, Laurentia and Gondwana fractured
- Antarctica and Australia split off Gondwana and moved south.
- A rift between South America and west coast of Africa opened South Atlantic, while India broke off the east coast of Africa, and began northward, ultimately smash into Asia and crumple up the Himalayan Mountains.
- Life evolved in harsh competition on larger landmasses, but evolution proceeded independently on isolated continents.
- Locations of mountain ranges and oceans altered climate.
- Animal Explosion:
- For the first time, green photosynthetic algae evolved to achieve a firm footing on swampy land; the continent were looking green at the edges.
- As atmospheric O soared in concentration, so did ozone layer - the radiation barrier.
- For 40M years, multicellular jelly fish and worms appear to have dominated the postglacial oceans.; rarely preserved in the fossil record.
- 530Ma, a striking evolutionary trick; many types of animals learned to build their own protective shells out of hard minerals (CaCO3 or SiO2).
- >Top Cambrian explosion:
- Explosion is a misleading moniker; it took many millions of years for 'biomineralization' to catch on.
- 580Ma, a few sponges with hardened spines appeared.
- 550Ma, the tail end of Ediacaran Period, a variety of wormlike creatures learned to craft carbonate minerals into tubeshaped protective homes on the ocean floor.
- 535Ma, the first recognizable shelly fauna appeared.
- >Top 530Ma, the real explosion occurred, when all manner of shelled animals suddenly came on the scene.
- An evolutionary arms race ensued. Armored predators and armored prey assumed larger and larger dimensions. Teeth and claws arose, bony protective plating and sharp defensive spine.
- Eyes became mandatory in the cutthroat world.
- Their carbonate bioskeletons contributed to massive limestone layers.
- 521-250Ma: wide-eyed sea creatures called trilobites are the most prized.
- Stephen Jay Gould 'Wonderful Life'; discovered at the Burgess Shale in BC, 505Ma site.
- Rhynie plant:
- leafless plants - the ancestors of our green world.
- >Top Prototaxites: appeared 420-379Ma.
- diameter 1m, and height reaching 8m, largest known living thing on land; a giant fungus, or largest toadstool in Earth's. history, having green stems and green branches but no leaves; a few small insects and spiderlike animals.
- For the first time in history, Earth's land was emerald green.
- >Top Mycorrhiza:
- Root systems evolved in remarkable ways as well.; new symbiotic relationships between plant roots and fungal filaments called mycorrhiza.
- This astonishing evolutionary strategy affects great majority of plants.
- The mycorrhizal fungi efficiently extract phosphate and other nutrients from the soil and pass them to the plant, which in turn provides the fungi with a steady diet of energy-rich glucose ad other carbohydrates.
- Animals' profound evolutionary advances:
- Insects, spiders, worms, and other small creatures were the first terrestrial explorers.
- 500Ma, primitive jawless fish,
- 420Ma, armored fish with bony-plated jaws.
- 400Ma, cartilaginous sharks and bony fish appeared.
- 397Ma, evolutionary transition from fins to four-footed land animals.
- 375Ma, four-legged land animal
- 340Ma, first true amphibians appeared (middle of Carboniferous)
- >Top Amphibian:
- characterized by broad, flat skulls, splayed legs, five-toed feet, ears suited for listening in air, and other terrestrial adaptations, were clearly different from their fish ancestors.
- Climate waxed and waned, droughts and floods stressed he land, and the odd asteroid impact and super volcano eruption.
- But Earth and its biota have proven unfailingly resilient to such insults. Life always finds a way to adapt to the reality of now.
- Third Great Oxidation Event:
>Top Mass Extinctions:
- 300Ma, Earth forests were flourishing, and buried C-rich black coal.
- The rise in O2 was gradual, from 18% of 380Ma, to 25% 350Ma, to remarkable 30% 300Ma.
- Ancient atmospheric bubbles in Carboniferous-age amber still hold 30% or more O2.
- Most dramatic were the giant insects; monster dragonflies with 70cm wingspans. The increase O2 also enhanced atmospheric density and made flying and gliding that much easier.
- 251Ma: the end of Permian, Paleozoic Era witnessed the greatest mass extinction.; 70% of land species and whopping 96% of marine species vanished - called the Great Dying.
- Never before or since in Earth history have so many creatures disappeared forever.
- What caused the Great Dying; like a giant steroid impact; indeed, multiple reinforcing stress factors might have come into play.
- O2 level rapidly dropped; from 35% to 20%.
- global cooling and a modes ice age, with thick ice covering the south portions of Pangaea.
- large drop in ocean levels exposing continental shelves, which are most productive biosphere.
- Large-scale volcanism at the end of Paleozoic Era.
- Depleted the ozone layer, opening the windows for mutagenic UV radiation.
- >Top Dinosaurs:
- 230 - 66Ma; Dinosaurs came on the scene as beneficiaries of the end-Paleozoic mass extinction (P-Tr), developed through (Tr-J) and became extinct at (K-T).
- These reptiles stared slow and small but diversified and radiated into ecological niche.
- Another significant extinction event (Tr-J) wipe out most nondinosaur vertebrates.; A dinosaur explosion followed.
- Mesozoic Era saw many important biological development; ammonite evolved.
- Pangaea began to break up, and the Atlantic Ocean was born.
- O2 rebounded to the present value of 21%.
- 65Ma; one of the worst days in Earth history. an asteroid about 10km in diameter collided with Earth near Yucatán Peninsula; followed by massive fires, immense clouds of vaporized rock darkened the skies and all but shut down photosynthesis.
- All dinosaurs except for one minor lineage - birds - went extinct. Ammonites also died out.
- Mammals: evolving small, rodentlike, footed in almost every ecological niche.
- Were there no mass extinction prior to 540Ma?
- There are almost no diagnostic fossils to record.
- Certainly life was severely challenged during the snowball Earth, perhaps during earlier glaciations. There cold have been hundreds of mass extinctions stretching back to the very dawn of life.
- Human Age:
- More than 99.9% of Earth's existence, there were no humans.
- Within a few million years of the dinosaurs' demise, mammals had radiated into vacant ecological niches. Many of these strange and wonderful new mammals died in other mass extinctions 56, 37, 34Ma.
- We all point to a common primate ancestor about 30Ma.
- The first hominids who walk erect, arose perhaps 8Ma in central Africa.
- Perhaps 8 separate times in the past 3M years, ice has spread from the poles reaching as far south as the upper Midwest. Ice bridges linked Asia and North America.
- Cold temperature favor the survival of infants who stay close to their mothers for longer periods, as well as infants with bigger heads. Big heads mean big brains.
- Warm interglacial periods, great retreats of seas followed by equally great advances. Such cycles were for the most part merciful; nomadic humans had plenty of time to move and survive.
- Aeons ago rocks, water, and air made life. Life, in turn, made the atmosphere safe to breath and made the land green and safe to roam. Life turned the rocks into soils that have nurtured more life and become home to an ever-widening array of flora and fauna.
- Throughout Earth history, air, seas, land, and life have been shaped by Earth's transformative powers; the power of sunlight and Earth's inner heat, the magic of water, the chemical power of C and O, and s¥ceaseless convention of the deep interior and consequent disruptions of the crust through earthquakes, volcanoes, and shifting continental plates
10. 緑の地球: 地表生物圏の登場
- Trilobite: 521-250Ma PT
diappeared in PT
- Prototaxites, a giant fungus
- 450-440Ma, O-S: Ordovician-Silurian extinction
- 375-360Ma, Late-D: Late Devonian extinction
- 252Ma, P-Tr: Permian-Triassic extinction
- 201.3Ma, Tr-J: Triassic-Jurassic extinction
- 66Ma, K-T: Cretaceous-Paleogene extincntion, Chicxulub impact
- 10K - ongoing, Holocene extinction; by possible causes of humans.