I’ve summarised the Earth’s climate for you below, a potted history of 4? billion years of changing climates:
? 4.5 billion years ago
The newly formed Earth had the hottest climate in it’s history with temperatures hot enough to melt rock. The decay of radioactive elements within Earth’s core generated intense heat and pressure. Along with volcanoes, this forced molten rock upward and outward toward Earth’s surface. Volcanoes emitted vast amounts of carbon dioxide into the atmosphere, causing the Greenhouse Effect.
? 3.8 billion years ago
The mass of radioactive material within Earth’s core diminished, this allowed the climate to cool and the first solid rocks formed. This led to a cooling of the atmosphere and allowed water vapour to liquefy, this fell to Earth as rain.
? 3.5 to 3 billion years ago
The earliest lifeforms evolved, these were plant-like photosynthetic algae. These algae absorbed carbon dioxide and released oxygen.
? 3 billion years ago
The algae reduced levels of carbon dioxide in the atmosphere, the greenhouse effect weakened and Earth entered it’s fist ice-age.
? 2.9 billion years ago
The intensity of the Sun increased as it steadily brightened. This additional heating brought the ice-age to an end. Seas and oceans began to form which moderated the climate of Earth. Ocean currents started circulating and transported warm waters from the Equatorial regions towards the poles.
? 800 to 550 million years ago
Ice-age conditions returned again, possibly caused by the orbit of the solar system around the galactic centre. As the ice advanced it froze vast sections of the oceans and killed the blooms of algae. As the amount of algae declined so too did it’s potential for sequestering carbon dioxide.
? 550 million years ago
The ever increasing concentration of atmospheric carbon dioxide ushered in a new period of global warming as a consequence of an enhanced greenhouse effect. This brought to a close the Late Proterezoic Ice Age and inaugurated a new period of climatic warmth.
? 542 million years ago.
The first multi-cellular lifeforms evolved, from which has evolved the diverse range of species that inhabit out planet today.
? 542 to 280 million years ago
The atmosphere was moderated, carbon dioxide levels were high and the planet experienced a period of warm temperatures. There were extensive carbon based lifeforms and lush vegetation, this was the Carboniferous Era.
? 230 million years ago
The drifting continental land-masses merged into a single landmass known as Pangea. Centred within the Equatorial region, Pangea had a warm, tropical climate.
? 135 to 65 million years ago
During the period of time known as the Cretaceous Era, temperatures were some 11°C warmer than they are today. Forests and tropical plants flourished in the polar regions and the ocean currents once again transported warm water to the polar regions.
? 65 million years ago
At least two enormous meteors impacted Earth* throwing up vast clouds of debris and other particulate matter, much of which came from immense forest fires that burned over areas of millions of square kilometres. This blocked out much of the heat from the Sun and in a period of just a few years the climate went from being considerably warmer than at present to considerably colder. This led to the rapid extinction of the dinosaurs and many of the marine species.
* Until recently it had been thought that a single meteor struck Earth, landing in what we now call the Gulf of Mexico. New research has discovered a similar impact crater dating from the same time in northern Siberia. One line of thinking is that Earth was bombarded by multiple meteors.
? The last 542 million years.
By using isotopic analysis of the fossilised remains of multi-cellular organisms it has been possible to reconstruct the climate for the last half a billion years or so. In doing so we can identify the approx 125 million year cycle that ties in with the orbit of the solar system around the galactic centre. This orbit produces temperature swings of 29°C with greater ice-ages occurring during the cold periods, during the warm periods all ice on the planet melts and the polar regions are warm enough to support extensive tree and plant growth.
Coupled with this major cycle are numerous shorter cycles that relate to the orbit of Earth within space, these cycles vary from 21,000 to 430,000 years. Each cycle has a warming and a cooling phase, the net effect of all cycles combined determines when Earth will cool and when it will warm.
The most noticeable of these cycles is the eccentricity or circularity of orbit around the Sun and it’s this cycle that produces the ice-ages at intervals of approx 100,000 years. The last of which ended nearly 10,000 years ago. It is also this cycle that caused the climate to be warmer than it is today, a situation that last occurred some 130,000 years ago.
Good question, Earth has had liquid water for billions of years, which is a puzzle (the faint young sun paradox) probably earths atmosphere was very high in CO2 (like Venus and Mars) but organisms like cyanobacteria evolved and began to convert CO2 to O2 by photosynthesis.
Since then CO2 has fluctuated wildly, but earths temperature has remained re-markedly steady, even during the ice ages it was only about 5C colder which is only about a 1% change.
My wild guess is it because we are a water world, 71% of our surface is water, and water acts to modulate and regulate our climate.
The Earth's first human recorded climate was perfect. Genesis will tell you that. Beyond that is anybodies guess.
Impossible to answer!!!
Trevor's "scientific" answer is "live" proof of how ignorant and arrogant scientists can be. He basis his answer on "carbon dating" which is very controversial in the first place. He tells his "story" as a matter of fact.
Your answer relies on either 'faith in human evolutionary science' (created by human science that explains a 4.5 billion year old Planet based on information accumulated within the last couple of thousand years with most of it gathered within the most recent 100 years) or 'faith in a supreme being' (written in scripture).
If someone you respect and admire tells you to go jump off of a cliff because it would be good for all of humanity, will you do it? Hence: "The leap of faith"
...didn't affect humans or any of the plants or animals we depend on to survive.
... didn't threaten to destroy hundreds of trillions of dollars worth of infrastructure.
.... is not the one we have now?
