History of the Earth

Ketaki Gaikwad

Earth Forms...

Earth was created 4.6 billion years ago, when our solar system took shape around the sun. The emerging Earth survived a massive collision that threw up the moon. Heat generated by the breakdown of radioactive elements, and the pressure of contraction meant the planet started out a molten mass. A rocky outer crust formed once it started to cool.

Asteroids and Comets...

4 billion years ago, millions of asteroids and comets slammed into the Earth's surface. These were not normal rocks but rather cosmic sponges, loaded with water that was released on impact. which then created the hydrosphere.

Oxygen enters the atmosphere...

3.5 billion years ago early bacterial life introduced oxygen to the atmosphere. As the first free oxygen was released through photosynthesis by cyanobacteria, it was initially soaked up by iron dissolved in the oceans. Once the iron in the oceans was used up, the iron oxide stopped being deposited and oxygen was able to start building up in the atmosphere about 2.4 billion years ago.

Snowball Earth...

Snowball Earth describes a theory that for millions of years the Earth was almost entirely covered in ice, stretching from a pole to a pole. This freezing happened over 650 million years ago in the Pre-Cambrain. Life could only cling on in ice-free areas, or where sunlight managed to sneak through the ice to allow photosynthesis.

Ordovician-Silurian mass extinction...

443 million years ago the third largest extinction in Earth's history, the Ordovician-Silurian mass extinction happened. This mass extinction had two dying times separated by hundreds of thousands of years. During the Ordovician, most life was in the sea, 85% of sea life was wiped out. A huge ice sheet in the southern hemisphere caused climate change and a fall in sea level. It also messed with the balance of the oceans.

Earliest Reptiles...

300 million years ago the earliest reptiles known as anapsids evolved from amphibians. Which resembled modern-day lizards. The first reptiles were small, agile species that lacked webbing on their feet.

Desert Earth...

A vast desert formed in Earth's prehistoric past when the supercontinent of Pangaea stretched to the poles. Pangaea's position influenced ocean circulation patterns, and its huge size meant that there were vast areas where moist air from the oceans never reached.

Supercontinent Breaks Up...

The giant supercontinent of Pangaea began breaking up toward the end of the Triassic. The process started with Europe's separation from Africa. Then the seaway pushed South America away from Central and North America, which in then began drifting apart from Europe, which formed the North Atlantic Ocean. The South Atlantic formed later when Africa and South America went their separate ways. These new seas acted as biological barriers, allowing different continents to develop their own distinct features.

Ice age...

The last ice age hasn't ended, the climate has just warmed up a bit causing the ice sheets to retreat back to the poles. Lots of the world's water was turned to ice, so precipitation was low. Globally, summer temperatures were 4-8 Celsius colder than today. In some places, the winter temperatures were 15-20 Celsius cooler than today. Wind speeds were higher and dust storms were common. 18,000 years ago the ice age was at its most extreme and the climate at its most severe.

Coal forests...

At the end of the Carboniferous, shallow seas drained away leaving coastal plains covered in swampy forests. These lasted right through until the Permian period. When leaves, branches and whole trees fell into the water, instead of decaying away they formed a layer of peat that would eventually become coal.

Citations

Earth Forms

"BBC Earth - Timeline - The Earth Formed from a Vast Gas and Dust Cloud." BBC - Homepage. N.p., n.d. Web. 23 Mar. 2015.

Asteroids and comets

"Where Does Water Come From?" HowStuffWorks. N.p., n.d. Web. 23 Mar. 2015.

Oxygen enters the atmosphere

"Prehistoric Time Line, Geologic Time Scale, Photos, Facts, Maps, and More." National Geographic. N.p., n.d. Web. 23 Mar. 2015.

Snowball Earth

"BBC Nature - Snowball Earth Videos, News and Facts." BBC - Homepage. N.p., n.d. Web. 23 Mar. 2015.

Ordovician-Silurian mass extinction

"BBC Nature - Ordovician-Silurian Mass Extinction Videos, News and Facts." BBC - Homepage. N.p., n.d. Web. 23 Mar. 2015.

Earliest Reptiles

"Prehistoric Time Line, Geologic Time Scale, Photos, Facts, Maps, and More." National Geographic. N.p., n.d. Web. 23 Mar. 2015.

Desert Earth

"BBC Nature - Desert Earth Videos, News and Facts." BBC - Homepage. N.p., n.d. Web. 23 Mar. 2015.

Supercontinent Breaks Up

"BBC Earth - Timeline - Pangaea is the Most Recent Supercontinent." BBC - Homepage. N.p., n.d. Web. 23 Mar. 2015.

Ice age

"BBC Nature - Ice Age Videos, News and Facts." BBC - Homepage. N.p., n.d. Web. 23 Mar. 2015.

Coal forests

"BBC Nature - Coal Forests Videos, News and Facts." BBC - Homepage. N.p., n.d. Web. 23 Mar. 2015.