We don’t know how, but our Universe came into existence as a pinpoint of extremely high temperature and massive energy.
By about 4 billion years ago the Earth was a completely formed planet, but it would have been unrecognisable to us now. The early Earth was volcanically hyperactive with a turbulent atmosphere of carbon dioxide, methane and water vapor. There was no breathable oxygen. Major volcanic activity, at its peak about 4 billion years ago continued for one or two billion years due to high heat flow from the planet's interior. Volcanic activity still occurs today – at a much-reduced severity.
Early organisms lived in an oxygen-free environment until around 2.4 to 2.3 billion years when the ‘Great Oxidation Event’ occurred when oxygen-producing cyanobacteria evolved and proliferated in the hot oceans.
The Earth may have gone through a ‘snowball’ phase 900-580 million years ago when the whole surface, including the oceans, was almost entirely ice. On warming up, multicellular life began to appear.
About 540 million years ago, there was a great increase in the diversity and complexity of life. This occurred in hot shallow seas near the equator. Geologists refer to this as the ‘Cambrian Explosion’.
This brought on the first (of five) mass extinction event but soon after this extinction event, evolutionary processes moved up a notch. By 420 million years ago plants and animals were firmly established on land and for the next 160 million years, climate was generally warm although major climate variations were experienced. Volcanic activity, mountain building episodes, changing ocean currents, glacier formation and other factors caused these climate variations. Major tectonic activity was a feature of this era as continents moved towards the formation of Pangea. The supercontinent Pangea existed from its formation roughly 335 million years ago for about 160 million years.
As the Earth cooled towards 360 million years ago there was a second mass extinction event. This heralded the beginning of the longest ice age since complex life developed. Known as the ‘Karoo Ice Age’, it lasted for 105 million years. This may be compared to our current geological ice age era of 2.6 million years - so far. This period may be called ‘the age of trees’ when huge forests grew and formed most of the coal deposits we have today. These forests soaked up much of the carbon dioxide in the atmosphere so by the end levels were similar to today at 200 to 500 ppm (parts per million) from levels in excess of 2,000ppm.
The greatest of all mass extinction occurred 251.9 million years ago probably due to massive basaltic lava flooding but despite the huge loss of species, evolution soon got to work and biodiversity was restored and then increased as the 'age of Dinosaurs’ was born. Plants also evolved with flowering plants appearing about 140 million years ago and grasses appearing by about 105 million years ago.
A large meteor impacted the Gulf of Mexico's Yucatán Peninsula creating the Chicxulub crater 66 million years ago and was followed by an "impact winter". Although having been around for many millions of years mammals were suddenly released from the threat of dinosaur predators to become the dominant type of animal as the world recovered from the extinction event. In today's world, the proportion of total mammal biomass made up of humans and our domestic animals is 96%.
During this early period global average temperatures were about 24 to 25 °C compared to 14 to 15 °C now. The climate was a ‘hothouse’ climate and there were forests at the poles – no ice.
Ten million years after the disastrous (for dinosaurs) meteor, there was a pronounced warm period - shortened from Palaeocene–Eocene Thermal Maximum. Although a short period in geological history (about 200,000 years) temperatures rose, in an already warm world, by about 5 to 8 °C. Mammals fared so well that we can trace the appearance of almost all current mammal species back to the PETM.
There followed a period when climate varied wildly with warmer and cooler periods. Sea level was much higher than now, and ocean circulation patterns varied quite drastically.
A fluctuating but falling trend set in for 50 million years with hotter and colder intervals and about 33.6 million years ago, the last major extinction event.
Huge variations in climate but ice existing at both poles. Very many advances of ice (glaciations) interspersed with warm interglacial periods. The current Holocene interglacial followed the hotter previous interglacial - the Eemian that ended over 100,000 years ago. Modern humans (and Neanderthals & Denisovans) have been around for over 300,000 years.
Starting 11,700 years ago at the end of the Younger Dryas cold snap, the Earth has experienced long warming and cooling periods interspersed with very many warm and cold snaps. The last cold snap, the Little Ice Age, petered out towards the end of the 19th century.
As the world warmed up from the coldest spell of the last 11,700 years, did a new climate-determining process take over?
Is climate now dominated by anthropogenic emissions as the latest anthropocentric theory maintains?
Or is climate still dominated by Natural Climate Variability - as it has for the last 540 million years?
Chapter 1 (pp 3-94) Reviews Phanerozoic time:
Chapter 1 (pp 94 - 119) Goes into more detail of the Eemian interglacial, the Younger Dryas cold snap and the Holocene including human evolution and civilisations (warm periods):
Chapter 1 (pp 119 - 173) reviews, in more detail, temperatures, Greenhouse gas levels, ice thickness and sea level over the last 540 million years with an emphasis on the recent Holocene interglacial period. The satellite era is reviewed. Note: there will be a more detailed review of temperatures and Greenhouse gases included on this website as new data becomes available.