Environment

Climate timeline - A short history of the Earth's climate

Confused by the idea of a snowball Earth or tropical Antarctica? Climate science can be baffling. Here is a very short history of the Earth’s climate that ...
Volcanoes have also shaped Earth\'s early climate by emitting large amounts of CO2/ Credits: Reuters

Fiery Birth: Hadean Era (Greek: underworld)
4.5 to 3.8 billion years ago 
In the beginning there was the bang. An exploding star, or supernova, created a cloud of gas and dust from which the solar system formed.

Nuclear fusion inside the sun provided light and heat for the young Earth, whose surface was liquid and molten hot. The atmosphere eventually cooled down enough for rain, creating the first ocean. 

Spark of life:  Archaean Era (Greek: beginning, origin)
3.8 to 2.5 billion years ago 
The first land masses appeared, and life developed. The oldest fossils date back to about 3.5 billion years ago. The atmosphere was still toxic, mainly consisting of ammonia and methane.  

This era is marked by the 'Faint Young Sun Paradox: the sun was only about 75 percent as bright as today, but Earth was not completely covered by ice. The planet was even warmer than today. Scientists assume that a greenhouse effect caused by high methane levels in the atmosphere prevented freezing. 

Oxygen Earth: Proterozoic Era (Greek: earlier life)
2.5 billion to 500 million years ago 
Atmospheric oxygen levels slowly started to increase fuelled by photosynthetic algae. This probably wiped out a huge portion of the Earth's anaerobic inhabitants, thus the era’s label as the 'oxygen catastrophe'. 

Evidence points to several periods of glaciation but little is known about their causes. Scientist still discuss a Snowball Earth scenario, where ice covered almost all of the planet.

Life Explodes: Paleozoic Era (Greek: ancient life)
500 to 250 million years ago 
The planet’s core finally cooled down to a level comparable to today. Volcanic eruptions became rarer. Earth generally saw a lot of glacial activity because the two primary supercontinents, Gondwana and Laurussia, drifted across the North and South Poles, receiving little solar energy.  

The rapid development of photosynthetic organisms made the air more breathable. During the so-called 'Cambrian Explosion' life in the oceans evolved rapidly from simple to complex forms. 

Jurassic Park: Mesozoic Era (Greek: middle animals)
250 to 65 million years ago 
Earth’s climate was mostly dry and highly seasonal with large temperature differences. When Pangaea, another one of the supercontinents, broke up into smaller units, more land came in contact with the oceans.

Humidity therefore increased and the climate became warmer and wetter. Temperatures were about 10 degrees Celsius higher than today and about the same everywhere, from the poles to the equator.

Mammals Master Earth: Cenozoic Era (Greek: new life)
65 to 2.7 million years ago 
Around 65 million years ago, an asteroid as big as the Isle of Wight smashed into what is today Mexico. The impact left a huge crater and rose a layer of dust that blanketed the Earth. Dinosaurs went extinct and mammals took over. The next time such volumes of similar dust particles appeared in the atmosphere was at the beginning of the Industrial Revolution.

About 55 million years ago, the planet experienced sudden warming. Methane bubbles, previously hidden beneath ice sheets, burst and further enhanced the warming trend. In just 20,000 years, global temperatures shot up five to eight degrees Celsius. The Earth was ice-free. During this warming event, similar amounts of carbon were released as have been by human activity. 

Some 33 million years ago, the first glaciers started to form in Antarctica, finally heralding an era of cooling. Ice sheets grew, sea levels fell. Instead of tropical forests, grasslands started to develop. This cooling trend culminated in the Ice Ages of the Pleistocene epoch.

Cooling down: Pleistocene Epoch (Greek: most new)
2.7 million to 12,000 years ago
When earth’s orbit changed and less solar energy hit the surface, which triggered the ice ages.

The planet had been almost ice-free for billions of years. Now, the advancing ice covered large parts of North America, Europe, and Asia. 

Cold glacial periods took turns with short warming spells, when glaciers retreated. It is estimated that there were between 25 and 30 ice ages and interglacials. During the coldest periods, average temperatures were about four to five degrees Celsius lower than today. 

Humanity Prevails: Holocene Epoch (Greek: entirely new)
12,000 years ago to present  
Around 12,000 years ago, the last ice age ended and Earth experienced a warming phase. But while other epochs were defined solely by natural and geological phenomena, the Holocene has become the period of human influence on biosphere and climate

By 1300 temperatures started to drop again, ushering in the 'Little Ice Age'. The direct sea route from Iceland to Greenland became impassable, due to the expansion of sea ice. From the 16th to 19th centuries, glaciers all over the world expanded.

The Western coast of Greenland began to submerge due to the increasing weight of ice sheets. The climate was too cold for satisfying crop yields, and famines struck Europe’s population.

From 950 to 1250, Earth experienced the 'Medieval Warm Period'. The Vikings started to emigrate to Iceland, Greenland, and Newfoundland. A severe drought caused the Maya civilization to collapse, but excellent weather in many other regions helped populations to grow.

Things changed abruptly in the 20th century as the planet began feeling the effects of the Industrial Revolution. Earth’s surface temperature rose on average by 0.7 degrees Celsius. The increase occurred in two periods—from approximately 1910 to 1944 and from 1978 to 1998. 

The British Meteorological Office predicts that 2010 will become the hottest year since the beginning of temperature records in 1880.


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