At one point, the Earth was a encased in a solid mantle of ice. The ice reflected so much of the heat from the sun that nothing would melt – it was locked in that condition. The key to unlock it was volcanic activity, where gas, dust and debris from inside the Earth itself started the melting process by reducing reflectivity, pumping greenhouse gas into the atmosphere, and allowing heat from the sun to be absorbed.
The initial melt was followed by a succession of ice-ages, interspersed with warmer periods. We are now towards the end of one of those warmer periods, and the Earth should be heading for the next ice-age if it were to follow the established sequence of events.
The difference in sea levels during an ice age and a warm period is measured in hundreds of feet.
The rotation of the Earth around its axis has slowed down. Records show that at one time a day was only 18 hours long, compared to 24 hours as we know it.
There have been reversals of the magnetic field around the Earth, and changes of axis of rotation.Continents are not in a fixed position, but are moving, very very slowly. At one time, there was just a single “supercontinent” – Pangea.The early atmosphere could not support life, as there was no Oxygen. Oxygen was formed by the photosynthetic combination of Carbon Dioxide with water. Only about 400 million years ago did the atmosphere contain enough Oxygen for the evolution of air-breathing land mammals.Although the atmosphere provides some protection against smaller objects from space, larger meteors will on occasion get through and impact with disatrous consequences. Scientists define five global mass extinctions in the past 500 million years. Three of these are thought to have been caused by meteor impacts.Volcanic activity is still a major influence on the planet. In 1453, Kuwae in Vanuatu exploded, splitting the island into two parts, and causing global cooling and disruption of harvests for two years. In 1815, Tamora, Indonesia erupted, again causing global disruption, and the “Year without a Summer”. As recently as 1991, Pinatubo, Philippines, erupted, much of the effluent being spread around the world via the Jet Stream, depressing global average temperature for two years.It is important to realise that the Earth is following a life-cycle, just as we do, with the same limitations. Just as it is impossible for us to revert to childhood and grow a new set of teeth, it is impossible for the Earth to go back in time and replenish the minerals, metals and oil that we are taking from its reserves. The conditions for their formation will never exist again.