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Engineer talking about concrete and rebar

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Engineer talking about concrete and rebar

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Cement how it's made  Learn the difference between cement and concrete  HD

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Articles on stuff

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Improve your students' reading comprehension with ReadWorks. Access thousands of high-quality, free K-12 articles, and create online assignments with them for your students.

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A source for science

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Visionlearning | Your insight into science

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Visionlearning is a free resource for the study of science, technology and math (STEM).

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Citation Machine®: Format & Generate - APA, MLA, & Chicago

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Citation Machine® helps students and professionals properly credit the information that they use. Cite sources in APA, MLA, Chicago, Turabian, and Harvard for free.

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Weather radar, wind and waves forecast for kiters, surfers, paragliders, pilots, sailors and anyone else. Worldwide animated weather map, with easy to use layers and precise spot forecast. METAR, TAF and NOTAMs for any airport in the World. SYNOP codes from weather stations and buoys.

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earth :: a global map of wind, weather, and ocean conditions

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See current wind, weather, ocean, and pollution conditions, as forecast by supercomputers, on an interactive animated map. Updated every three hours.

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Lewis & Clark: The Journey of the Corps of Discovery is a production of Florentine Films and WETA, Washington, D.C.

Inside the Corps
Enter the world of Lewis, Clark and the rest of the Corps of Discovery.

Native Americans
Indian tribes already knew the lands that Lewis and Clark discovered.

The Archive
Follow an expedition timeline and maps, or read the journals of the Corps.

Into the Unknown
In this interactive story, you're leading the expedition now.

Interactive Trail Map
Follow Lewis and Clark on their journey through 11 states, with journal entries, Native American history, and events to celebrate the expedition's bicentennial.

Classroom Resources
Explore the significance of the expedition using lesson plans and activities.

Living History
Listen to expert historians give their thoughts on the expedition.

A Forum with Ken Burns
Meet the director of "Lewis and Clark" and ask him your questions.

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Lewis & Clark: The Journey of the Corps of Discovery is a production of Florentine Films and WETA, Washington, D.C. Inside the Corps Enter the world of Lewis, Clark and the rest of the Corps of Discovery. Native Americans Indian tribes already knew the lands that Lewis and Clark discovered.

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A good resource for people who think!

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ThoughtCo.com is the World's Largest Education Resource

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From chemistry to computer programming, arts to World War II, ThoughtCo.com provides guides, tips, and resources to help you understand more about the world around us.

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In prep by class of 2020

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1. Rignot, E., Jacobs, S., Mouginot, J., and Scheuchl, B. (2013). Ice Shelf Melting Around Antarctica. Science.

2. Holland, P.R., Corr, H.F.J., Vaughan, D.G., Jenkins, A., and Skvarca, P., 2009. Marine ice in Larsen Ice Shelf. Geophysical Research Letters, 2009. 36: p. L11604.

3. Morris, E.M. and Vaughan, A.P.M., 2003. Spatial and temporal variation of surface temperature on the Antarctic Peninsula and the limit of viability of ice shelves, in Antarctic Peninsula climate variability: historical and palaeoenvironmental perspectives, E.W. Domack, et al., Editors. American Geophysical Union, Antarctic Research Series, Volume 79: Washington, D.C. p. 61-68.

4. Cook, A.J. and Vaughan, D.G., 2010. Overview of areal changes of the ice shelves on the Antarctic Peninsula over the past 50 years. The Cryosphere, 2010. 4(1): p. 77-98.

5. Scambos, T., Hulbe, C., and Fahnestock, M., 2003. Climate-induced ice shelf disintegration in the Antarctic Peninsula, in Antarctic Peninsula climate variability: historical and palaeoenvironmental perspectives, E.W. Domack, et al., Editors. American Geophysical Union, Antarctic Research Series, Volume 79: Washington, D.C. p. 79-92.

6. Rott, H., Skvarca, P., and Nagler, T., 1996. Rapid collapse of northern Larsen Ice Shelf, Antarctica. Science, 1996. 271(5250): p. 788-792.

7. Pudsey, C.J. and Evans, J., 2001. First survey of Antarctic sub-ice shelf sediments reveals Mid-Holocene ice shelf retreat. Geology, 2001. 29: p. 787-790.

8. Domack, E., Duran, D., Leventer, A., Ishman, S., Doane, S., McCallum, S., Amblas, D., Ring, J., Gilbert, R., and Prentice, M., 2005. Stability of the Larsen B ice shelf on the Antarctic Peninsula during the Holocene epoch. Nature, 2005. 436(4): p. 681-685.

9. Pritchard, H.D., Ligtenberg, S.R.M., Fricker, H.A., Vaughan, D.G., van den Broeke, M.R., and Padman, L., 2012. Antarctic ice-sheet loss driven by basal melting of ice shelves. Nature, 2012. 484(7395): p. 502-505.

10. Shepherd, A., Wingham, D., and Rignot, E., 2004. Warm ocean is eroding West Antarctic Ice Sheet. Geophysical Research Letters, 2004. 31(23): p. L23402.

11. Glasser, N.F. and Scambos, T.A., 2008. A structural glaciological analysis of the 2002 Larsen B ice shelf collapse. Journal of Glaciology, 2008. 54(184): p. 3-16.

12. Scambos, T., Fricker, H.A., Liu, C.-C., Bohlander, J., Fastook, J., Sargent, A., Massom, R., and Wu, A.-M., 2009. Ice shelf disintegration by plate bending and hydro-fracture: Satellite observations and model results of the 2008 Wilkins ice shelf break-ups. Earth and Planetary Science Letters, 2009. 280(1â€"4): p. 51-60.

13. MacAyeal, D.R., Scambos, T.A., Hulbe, C.L., and Fahnestock, M.A., 2003. Catastrophic ice-shelf break-up by an ice-shelf-fragment-capsize mechanism. Journal of Glaciology, 2003. 49(164): p. 22-36.

14. Dupont, T.K. and Alley, R.B., 2006. Role of small ice shelves in sea-level rise. Geophys. Res. Lett., 2006. 33(9): p. L09503.

15. Dupont, T.K. and Alley, R.B., 2005. Assessment of the importance of ice-shelf buttressing to ice-sheet flow. Geophys. Res. Lett., 2005. 32(4): p. L04503.

16. Scambos, T.A., Bohlander, J.A., Shuman, C.A., and Skvarca, P., 2004. Glacier acceleration and thinning after ice shelf collapse in the Larsen B embayment, Antarctica. Geophysical Research Letters, 2004. 31: p. L18402.

17. Rott, H., Müller, F., and Floricioiu, D., 2011. The Imbalance of glaciers after disintegration of Larsen B ice shelf, Antarctic Peninsula. The Cryosphere, 2011. 5: p. 125-134.

18. Hulbe, C.L., Scambos, T.A., Youngberg, T., and Lamb, A.K., 2008. Patterns of glacier response to disintegration of the Larsen B ice shelf, Antarctic Peninsula. Global and Planetary Change, 2008. 63(1): p. 1-8.

19. Rott, H., Rack, W., Nagler, T., and Ieee. 2007. Increased export of grounded ice after the collapse of northern Larsen Ice Shelf, Antarctic Peninsula, observed by Envisat ASAR, in Igarss: 2007 Ieee International Geoscience and Remote Sensing Symposium, Vols 1-12 - Sensing and Understanding Our Planet. p. 1174-1176.

20. Glasser, N.F., Scambos, T.A., Bohlander, J., Truffer, M., Pettit, E., & Davies, B.J., 2011. From ice-shelf tributary to tidewater glacier: continued glacier recession, acceleration and thinning following the 1995 collapse of the Prince Gustav Ice Shelf on the Antarctic Peninsula. Journal of Glaciology 57, 397-406.

21. Davies, B.J., Carrivick, J.L., Glasser, N.F., Hambrey, M.J., & Smellie, J.S., 2012. Variable glacier response to atmospheric warming, northern Antarctic Peninsula, 1988-2009. The Cryosphere 6, 1031-1048. doi:10.5194/tc-6-1031-2012

22. Joughin, I. and Alley, R.B., 2011. Stability of the West Antarctic ice sheet in a warming world. Nature Geosci, 2011. 4(8): p. 506-513.

# data[].attributes.attachment_link.description
1. Rignot, E., Jacobs, S., Mouginot, J., and Scheuchl, B. (2013). Ice Shelf Melting Around Antarctica. Science. 2. Holland, P.R., Corr, H.F.J., Vaughan, D.G., Jenkins, A., and Skvarca, P., 2009. Marine ice in Larsen Ice Shelf. Geophysical Research Letters, 2009. 36: p. L11604. 3. Morris, E.M. and Vaughan, A.P.M., 2003.

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For all grades

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Learn about the ancient Egyptian civilization and what they did in their daily lives. Many things like metal work, paper making and amazing architecture all came from the Egyptians.

When where the Pyramids built check here
View All History of Egypt

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History for Kids - Fun Facts and Social Studies

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History for kids Welcome to History for Kids the free online history network. We hope you enjoy and have fun exploring our history. The website is packed with articles, worksheets and even a quiz on each section. You will find cool games, videos, worksheets on many historical events that will help you understand those that ...

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A continuing slide show of current science (or not)

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SOCCOM | Unlocking the Mysteries of the Southern Ocean

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The Southern Ocean Carbon and Climate Observations and Modeling project (SOCCOM) is a multi-institutional program focused on unlocking the mysteries of the Southern Ocean and determining its influence on climate. Housed at Princeton University and administered by the Princeton Environmental Institute, SOCCOM is supported by the National Science Foundation under NSF Award PLR-1425989.

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LOTS of information for our timeline

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Astronomical and geological evidence indicates that the Universe is approximately 13,820 million years old[42], and our solar system is about 4,567 million years old. Earth's Moon formed 4,450 million years ago, just 50 million years after the Earth's formation.

Because the composition of the rocks retrieved from the Moon by the Apollo missions is very similar to rocks from the Earth, it is thought that the Moon formed as a result of a collision between the young Earth and a Mars-sized body, sometimes called Theia, which accreted at a Lagrangian point 60° ahead or behind the Earth. A cataclysmic meteorite bombardment (the Late Heavy Bombardment) of the Moon and the Earth 3,900 million years ago is thought to have been caused by impacts of planetesimals which were originally beyond the Earth, but whose orbits were destabilized by the migration of Jupiter and Saturn during the formation of the solar system. The Mars Reconnaissance Orbiter and the Mars Global Surveyor have found evidence that the Borealis basin in the northern hemisphere of Mars may have been created by a colossal impact with an object 2,000 kilometers in diameter at the time of the Late Heavy Bombardment.[20]

Approximately 4,000 million years ago, the earth was cool enough for land masses to form. The supercontinent Rodinia was formed about 1100 million years ago, and it broke into several pieces that drifted apart 750 million years ago. Those pieces came back together about 600 million years ago, forming the Pan-African mountains in a new supercontinent called Pannotia. Pannotia started breaking up 550 million years ago to form Laurasia and Gondwana. Laurasia included what are now North America, Europe, Siberia, and Greenland. Gondwana included what is now India, Africa, South America, and Antarctica. Laurasia and Gondwana rejoined approximately 275 million years ago to form the supercontinent Pangea. The break up of Pangea, which still goes on today, has contributed to the formation of the Atlantic Ocean.

(mya = million years ago)
The times are approximate and may vary by a few million years.

Precambrian Time
(4567 to 542 mya)

- 4650 mya: Formation of chondrules in the Solar Nebula
- 4567 mya: Formation of the Solar System
Sun was only 70% as bright as today.
- 4500 mya: Formation of the Earth.
Formation of the Moon
- 4450 mya: The Moon accretes from fragments
of a collision between the Earth and a planetoid;
Moon's orbit is beyond 64,000 km from the Earth.[33]
Earth day is 7 hours long[34]
- Earth's original hydrogen and helium atmosphere
escapes Earth's gravity.
- 4455 mya: Tidal locking causes one side
of the Moon to face the Earth permanently.[30]
- 4280 mya: Water started condensing in liquid form.
- 3900 mya: Cataclysmic meteorite bombardment.
The Moon is 282,000 km from Earth.[34]
Earth day is 14.4 hours long[34]
- Earth's atmosphere becomes mostly
carbon dioxide, water vapor,
methane, and ammonia.
- Formation of carbonate minerals starts
reducing atmospheric carbon dioxide.
- There is no geologic record for the Hadean Eon.

stromatolites Eoarchean Era (4000 to 3600 mya)

- 4000 mya: The Earth's crust cooled and solidified.
- Atmospheric pressure ranged from 100 to 10 bar.
- Earth day is 15 hours long
Paleoarchean Era (3600 to 3200 mya)
Start of Plate Tectonics
- 3600 mya: Formation of first supercontinent Vaalbara.
- 3500 mya: Monocellular life started (Prokaryotes).
First known oxygen-producing bacteria:

cyanobacteria (blue-green algae) form
- Oldest unambiguous microfossils date from this era.
Mesoarchean Era (3200 to 2800 mya)
- 3000 mya: Atmosphere has 75% nitrogen,
15% carbon dioxide.
- Sun brightens to 80% of current level.
- 2900 mya: Pongola glaciation occurred.
Neoarchean Era (2800 to 2500 mya)
- 2800 mya: Break up of supercontinent Vaalbara.
- Oldest record of Earth's magnetic field.
- 2700 mya: Supercontinent Kenorland formed.
- Photosynthetic organisms proliferate.

Dickinsonia Paleoproterozoic Era (2500 to 1600 mya)
Siderian Period (2500 to 2300 mya)
- Stable continents first appeared.
- 2500 mya: First free oxygen is found
in the oceans and atmosphere.
Banded Iron Formations
- 2400 mya: Great Oxidation Event,
also called the Oxygen Catastrophe.
Oxidation precipitates dissolved iron
creating banded iron formations.[14]
Anaerobic organisms are poisoned by oxygen.
- 2400 mya: Start of Huronian ice age
Rhyacian Period (2300 to 2050 mya)
- 2200 mya: Organisms with mitochondria
capable of aerobic respiration appear.
- 2100 mya: End of Huronian ice age
Orosirian Period (2050 to 1800 mya)
- Intensive orogeny (mountain development)
- 2023 mya: Meteor impact, 300 km crater
Vredefort, South Africa [9]
- 2000 mya: Solar luminosity is 85% of current level.
- Oxygen starts accumulating in the atmosphere
- 1850 mya: Meteor impact, 250 km crater
Sudbury, Ontario, Canada [9]
Statherian Period (1800 to 1600 mya)
- 1800 mya: Supercontinent Columbia (Nuna) formed.
- Complex single-celled life appeared.
- Abundant bacteria and archaeans.
Mesoproterozoic Era (1600 to 1000 mya)
Calymmian Period (1600 to 1400 mya)
- Photosynthetic organisms continue to proliferate.
- Oxygen builds up in the atmosphere above 10%.
- Formation of ozone layer starts blocking
ultraviolet radiation from the sun.
- 1600 mya: Eukaryotic (nucleated) cells appear.
Origin of ancestor of all animals, plants and fungi

Ectasian Period (1400 to 1200 mya)
- Green (Chlorobionta) and red (Rhodophyta) algae abound.
Stenian Period (1200 to 1000 mya)
- 1200 mya: Spore/gamete formation indicates
origin of sexual reproduction.[36]
- 1100 mya: Formation of the supercontinent Rodinia

Neoproterozoic Era (1000 to 542 mya)
Tonian Period (1000 to 850 mya)
- 1000 mya: Multicellular organisms appear.
- 950 mya: Start of Stuartian-Varangian ice age
- 900 mya: Earth day is 18 hours long.
The Moon is 350,000 km from Earth.[31]
Cryogenian Period (850 to 630 mya)

- 750 mya: Breakup of Rodinia
- 650 mya: * Mass extinction of 70% of dominant sea plants
due to global glaciation ("Snowball Earth" hypothesis).
The Moon is 357,000 km from Earth.[31]
Ediacaran (Vendian) Period (630 to 542 mya)
- 600 mya: Formation of the supercontinent Pannotia
Earth day is 20.7 hours long.[35]
- 590 mya: Meteor impact, 90 km crater
Acraman, South Australia

- 580 mya: Soft-bodied organisms developed:
Jellyfish, Tribrachidium, and
- 570 mya: End of Stuartian-Varangian ice age appeared.
Shelled invertebrates appeared
- 550 mya: Pannotia fragmented into Laurasia and Gondwana

Phanerozoic Eon
(542 mya to present)

Tiktaalik Cambrian Period (542 to 488.3 mya)
- Abundance of multicellular life.
- Most of the major groups of animals first appear
Tommotian Stage (534 to 530 mya)
- 510 mya: Vertebrates appeared in the ocean.
Solar brightness was 6% less than today.
Ordovician Period (488.3 to 443.7 mya)

- diverse marine invertebrates, such as trilobites,
became common
- First green plants and fungi on land.
- Fall in atmospheric carbon dioxide.
- 450 mya: Start of Andean-Saharan ice age.
- 443 mya: Glaciation of Gondwana.
* Mass extinction of many marine invertebrates.
Second largest mass extinction event.
49% of genera of fauna disappeared.
Silurian Period (443.7 to 416 mya)

- 420 mya: End of Andean-Saharan ice age.
- Stabilization of the earth's climate
- Land plants and coral reefs appeared
- First fish with jaws - sharks
- Insects (spiders, centipedes), and plants appear on land
Devonian Period (416 to 359.2 mya)

- Ferns and seed-bearing plants (gymnosperms) appeared
- Formation of the first forests
- Earth day is ~21.8 hours long.
- 400 mya: Land animals appeared, wingless insects
- 376 mya: Viluy Traps Large Igneous Province volcanic eruption
- 375 mya: Vertebrates with legs, such as
- Atmospheric oxygen level is about 16% appeared.

- First amphibians appear.
- 374 mya: * Mass extinction of 70% of marine species.
This was a prolonged series of extinctions
occurring over 20 million years.
Evidence of anoxia in oceanic bottom waters,
and global cooling. Surface temperatures dropped
from about 93°F (34°C) to about 78°F (26°C)
- 370 mya: First trees appeared
- 359 mya: Meteor impact, 40 km crater
Woodleigh, Australia
Carboniferous Period (359.2 to 299 mya)
Mississippian Epoch (359.2 to 318.1 mya)
(Lower Carboniferous)
- 350 mya: Beginning of Karoo ice age.

- Large primitive trees develop
- First winged insects
- Forests consist of ferns, club mosses, horsetails, and gymnosperms.
- Oxygen levels increase
- 324 mya: Synapsid vertebrates, the ancestors of mammals,
appear on land.
- Seas covered parts of the continents
- Animals laying amniote eggs appear (318 mya)
Pennsylvanian Epoch (318.1 to 299 mya)
(Upper Carboniferous)
- 300 mya: First reptiles (diapsids) appeared.
They were ancestors of crocodiles, dinosaurs and pterosaurs.
- Atmospheric oxygen levels reach over 30%
- Earth day is ~22.4 hours long.
The Moon is 375,000 km from Earth.[31]

- Giant arthropods populate the land
- Transgression and regression of the seas
caused by glaciation
- Deposits of coal form in Europe, Asia,
and North America
Permian Period (299 to 251 mya)

- 275 mya: Formation of the supercontinent Pangea

- Conifers and cycads first appear
- Earth is cold and dry

- Sail-backed synapsids like
Edaphosaurus and Dimetrodon appeared
- 260 mya: End of Karoo ice age.
- 252 mya: Period of great volcanism in Siberia
Siberian Traps Large Igneous Province releases
large volume of gases (CO ₂, CH ₄, and H ₂S) [8]
- Oxygen (O ₂) levels dropped from 30% to 12%
Carbon dioxide (CO ₂) level was about 2000 ppm
Temperatures reach 50-60°C on land, and 40°C at the sea-surface.[37]
- 251 mya: * Mass extinction (Permian-Triassic)
- Possible 480km-wide meteor crater in the
Wilkes Land region of Antarctica [26]
Earth's worst mass extinction eliminated
90% of ocean dwellers, and 70% of land
plants and animals.

Triassic Period (251 to 199.6 mya)

- Break-up of Pangaea starts
- Survivors of P-T extinction spread and recolonize

- Reptiles populate the land.
- 240 mya: Sea urchins ( Arkarua) appear
- 235 mya: Evolutionary split between dinosaurs and lizards
- Giant marine ichthyosaurs and plesiosaurs populate the seas
- First small dinosaurs such as coelophysis appear on land
- Adelobasileus proto-mammal emerged (225 mya)

- 214 mya: Meteor impact, 100 km crater
Manicouagan, Quebec, Canada [9]
- 205 mya: First evidence of mammals: Morganucodon
- 201 mya: Central Atlantic Large Igneous Province volcanic eruption[38]
* Mass extinction killed 20% of all marine families
Jurassic Period (199.6 to 145.5 mya)
- Earth is warm. There is no polar ice
- Cycads, conifers and ginkgoes are the dominant plants
- Age of the dinosaurs
- Giant herbivores and vicious carnivores
dominate the land
- Flying reptiles (Pterosaurs) appeared.

- 180 mya: North America separates from Africa

- 167 mya: Meteor impact, 80 km crater
Puchezh-Katunki, Russia [9]
- 166 mya: Evolutionary split of monotremes from primitive mammals

- 150 mya: First birds like Archaeopteryx appear
- 148 mya: Evolutionary split between
marsupial and eutherian mammals
- 145 mya: Meteor impact, 70 km crater
Morokweng, South Africa [9]
Cretaceous Period (145.5 to 65.5 mya)
- Period of Active Crust Plate Movements
- 133 mya: Meteor impact, 55 km crater
Tookoonooka, Australia [9]
- 125 mya: Africa and India separate from Antarctica

- Flowering plants (angiosperms) appeared
Montsechia vidalli was one of the first angiosperms.
- 120 mya: Global warming event starts
Carbon dioxide levels were 550 to 590 ppm [27]
- Proliferation of single-cell organisms (diatoms, dinoflagellates,
and calcareous nannoplankton) changed ocean composition.
- 116 mya: First birds with beaks without teeth.
- 110 mya: Crocodiles appeared
- Snakes evolved during the mid-Cretaceous
- 105 mya: South America breaks away from Africa
- Formation of the Atlantic Ocean

- Earth has no polar ice
- Oldest group of living placental mammals developed
- 100 mya: Earth's magnetic field is
3 times stronger than today.

First ants (hymenoptera) appeared
- 90 mya: Global warming event ends
- Western Interior Seaway separates North America
into Laramidia (west) and Appalachia (east)
- 85 mya: Australia starts to separate from Antarctica
Dinilysia Patagonica - first snake without legs [44]
- 70 mya: Meteor impact, 65 km crater
Kara, Russia [9]
Your browser does not support the audio element.
- 68 mya: Tyrannosaurus rex thrived Caution: Do not poke T. rex
- 67.5 mya: Deccan Traps Large Igneous Province volcanic eruptions
start in India and produce great volume of lava and gases.

- 65.5 mya: Meteor impact, 170 km crater
Chicxulub, Yucatan, Mexico [9]
- * Mass extinction of 80-90% of marine species
and 85% of land species, including the dinosaurs.

Miocene Epoch (23.03 to 5.3 mya)
- African-Arabian plate joined to Asia
- 21 to 14 mya: Miocene warming period
- 14 mya: Circum-polar ocean circulation builds up Antarctic ice cap.
- 14 to 6 mya: Global temperature drops by 4°C.
- First raccoons appear.
- Drying of continental interiors
- Forests give way to grasslands
- 6 mya: Upright walking (bipedal) hominins appear
Pliocene Epoch (5.3 to 2.58 mya)
- 4.4 mya: Appearance of Ardipithecus, an early hominin genus.
- 4 mya: North and South America join at the Isthmus of Panama.
Animals and plants cross the new land bridge.
Ocean currents change in the newly isolated Atlantic Ocean.

- 3.9 mya: Appearance of Australopithecus, genus of hominids.
- 3.7 mya: Australopithecus hominids inhabit Eastern and Northern Africa.
- 3 mya: Formation of Arctic ice cap.
- Accumulation of ice at the poles
- Climate became cooler and drier.
- Spread of grasslands and savannas
- Rise of long-legged grazing animals
Quaternary Period (2.58 mya to today)
Pleistocene Epoch (2.58 mya to 11,400 yrs ago)
- Several major episodes of global cooling, or glaciations

- 2.4 mya: Homo habilis appeared
- 2.1 mya: Yellowstone supervolcanic eruption
- 2 mya: Tool-making humanoids emerge.
Beginning of the Stone Age.
- 1.7 mya: Homo erectus first moves out of Africa
- 1.3 mya: Yellowstone supervolcanic eruption
- 1.3 mya to 820,000 yrs ago: Sherwin Glaciation
- Presence of large land mammals and birds
- 790,000 yrs ago: First use of fire by hominds[40]
- 700,000 yrs ago: Human and Neanderthal lineages start to diverge genetically.
- 680,000 to 620,000 yrs ago: Günz/Nebraskan glacial period
- 640,000 yrs ago: Yellowstone supervolcanic eruption
- 530,000 yrs ago: Development of speech in Homo Heidelbergensis[15]
- 455,000 to 300,000 yrs ago: Mindel/Kansan glacial period
- 400,000 yrs ago: Hominids hunt with wooden spears
and use stone cutting tools.
- 370,000 yrs ago: Human ancestors and Neanderthals
are fully separate populations.

- 12,900 yrs ago:

Extinction Events
There have been five major mass extinctions events: the terminal Ordovician (443 mya), Late Devonian (374 mya), terminal Permian called the "Great Dying" (251 mya), terminal Triassic (201), and terminal Cretaceous called the K/T event (65.5 mya). The Ordovician extinction was caused by global cooling and glaciation. The other four are associated with prolonged volcanism in large igneous provinces, although a meteorite impact also contributed to the K/T event.

Humans as agents of environmental change
Some scientists have tried to correlate the migration of humans to America with the extinction of the megafauna of the Pleistocene Epoch while others feel that weather changes brought about by the explosion of an asteroid or comet over North America might have been responsible.[25] There is no doubt that human activities can have a substantial impact on the environment and native species. The dodo, a flightless bird indigenous to Mauritius, became extinct in the late 17th century from massive hunting and the introduction of animals such as dogs, pigs, and cats. The Passenger Pigeon went from being the most common bird in North America to extinction by the end of the 19th century due to hunting and loss of habitat by deforestation. Overfishing the costal waters of California in 1945 produced 235,000 tons of fish, but in 1948 only 15,000 tons of fish were caught which led to the collapse of Cannery Row. The Dust Bowl was a man-made ecological disaster caused by deep plowing of the top soil of the Great Plains which destroyed native grasses whose roots had protected the soil from erosion. Drought and wind created a period of severe dust storms between 1930 and 1936. Soils that had been fertile became incapable of growing crops after the top soil was blown away. The contemporary destruction of tropical forests by the logging industry and the large-scale clearing of forests to plant commercial crops is already having harmful ecological effects that are likely to become worse if non-sustainable practices continue to be used.

The Earth's near-term future
Human industrial activity that relies on burning fossil fuels, such as coal and petroleum products, has been generating the greenhouse gases carbon dioxide (CO ₂), methane (CH ₄), and nitrous oxide (N ₂ O), in large quantities since about 1750. The chart below shows the levels of atmospheric carbon dioxide during the last millennium and its sharp rise during the last century.[2] Atmospheric models predict that elevated greenhouse gases will cause global warming and influence weather patterns that will melt polar ice and destroy the habitat of animals such as the polar bear. The increase of global temperatures will also reduce the amount of snow deposited on mountains thus decreasing the flow of water in rivers which are now used for navigation, irrigation, and as sources of potable water. Carbon dioxide will also increase the acidity of sea water and threaten coral reefs and shell-building oceanic life forms.

As of February 2016, the monthly average level of carbon dioxide was 404.02 ppm at the National Oceanic & Atmospheric Administration (NOAA) laboratory in Mauna Loa, Hawaii, and the level continues to increase steadily. In the following image, the dashed red line represents the monthly mean values of CO ₂ with the points centered on the middle of each month. The black line represents the same, after correction for the average seasonal cycle.

Analysis of core sediments in the Arctic Circle indicate that 55 million years ago, the carbon dioxide concentration was 2,000 ppm and the North Pole's temperature averaged 23°C (73.4°F) compared to a mean annual temperature of -20°C today.[4] Satellite images by NASA show approximately a 20% reduction in the Earth's minimum ice cover between 1979 and 2003.[5] Arctic perennial sea ice has been decreasing at a rate of 9% every ten years. At this rate, the summertime Arctic Ocean will be ice-free before the year 2100.

There is a large amount of water stored as ice over the landmasses of Greenland and Antarctica. If the ice sheets melt, the resulting rise in global sea level will flood many coastal areas around the world. The Greenland ice sheet contains enough water to increase the global sea level by 24 feet (7.3 meters), the West Antarctic ice sheet could raise sea level by 19 feet (5.8 meters), and the East Antarctic ice sheet could raise the sea level globally by 170 feet (51.8 meters).[12] The combined effect of melting all the ice on Greenland and Antarctica would result in a sea level rise of 213 feet (65 meters).

Using computer models, scientists at the University of Arizona Department of Geosciences have created maps that show areas susceptible to rises in sea level (in red). The following map shows that a 6-meter (20-foot) rise would flood Miami, Fort Lauderdale, Tampa, and the entire Florida coastline, as well as parts of Orlando and other inland areas. Most of the city of New Orleans, Louisiana will disappear under water if the sea rises six meters. Some scientists have warned that by the year 2200, at the current rate of greenhouse gas emissions from human activities, the atmospheric levels of carbon dioxide, methane, and nitrous oxide will be at the same levels associated with mass-extinction events in the Earth's past.[8]

The Earth's long-term future
The future of the Earth is linked to the fate of the Sun. The Sun is halfway through its life cycle and will exhaust its supply of hydrogen fuel in around 4,000 million years. As the Sun cools, its core will collapse and its atmosphere will expand transforming the Sun into a red giant star. The swelling Sun will engulf the planets closest to it, and the Earth will be completely vaporized. The Sun will die in several stages. When its core crashes inwards, it will start fusing helium atoms into carbon. When the helium supply runs out, the center will collapse again and form a white dwarf star that will become dimmer until its light finally fades. The final collapse of stars which are a few times larger than the Sun ends in a massive supernova explosion that leaves behind a rapidly spinning neutron star.

Long before the Sun becomes a white dwarf, 2,000 million years from now, our Milky Way Galaxy is predicted to collide with the Andromeda Galaxy.[13] The collision will take place for several million years and result in one combined super galaxy named Milkomeda. The sun may become part of the Andromeda system during the collision and could eventually end up far away from the new merged galactic center. The Earth may also eventually lose its Moon. Scientists using the laser ranging retroreflector positioned on the Moon in 1969 by the Apollo 11 astronauts have determined that the Moon is receding from Earth at a rate of about 3.8 centimeters per year.

(my = millions of years)

Earth's Long-Term Future

+200 years: Possible global warming event caused by anthropogenic carbon dioxide (CO ₂)[8]
+1500 my: Sun is about 6000 million years old and 15% brighter than today.
+2000 my: Milky Way Galaxy starts colliding with Andromeda Galaxy.[13]
+3000 my: Solar system becomes part of the new Milkomeda Galaxy.
+4000 my: Sun is about twice as bright as today and its radius is 40% greater.
Sun starts to exhaust its supply of hydrogen.
+5000 my: Sun starts changing into a red giant star, 3 times its present size.[18]
Earth is engulfed by the red giant Sun.
+10000 my: Red giant Sun collapses and becomes a white dwarf.
+20000 my: White dwarf Sun becomes a black dwarf.

Frequent misspellings of geologic terms and Evolutionary periods of the Earth:
creataceous, cretaceus, cretacous, jurassique, jurasik, jurasic, jurossic, myscene, myocene, myoscene, phanaerozoic, triasic

© Copyright 2012 - Antonio Zamora

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