Introduction

The history of the earth over the last several hundred million years is recorded and contained in the layers of the earth, the rocks. Throughout the history of the earth, the evolution of plants, animals, and man were influenced by major geologic events that changed life on earth. This BLOG is an attempt to list chronologically from 4 billion years ago to today those events that were so disruptive to life on earth, that mankind, indeed every living thing, was affected. It is a collection of scientific articles about volcanic eruptions instantly changing the earths temperature and weather patterns, large meteorites hitting the earth, and a host of interesting geologic events that affected life on earth. For example, Mount Tambora erupts in 1815, causing the Year Without a Summer in Europe and North America had a volcanic winter. Atmospheric CO2 levels start creeping from 100 ppmv 15,000 years ago at the end of the last glaciation to the current level of 385 parts per million volume (ppmv). According to some sources the CO2 levels are a significant factor causing global warming and climate change, possibly from anthropogenic sources, such as the Industrial Revolution. Other sources believe the Sun is the key driver to climate change and hence the global warming we are experiencing today. Radiation from the sun contributes to variations in temperature on the earth. Therefore, the suns natural cycles are the primary driver to the earths natural cycles.






The changes about to happen to us today and in the near future have occurred in the past and their stories are told in the rocks beneath our feet.

We hope you find this story of the earth and man evolving on this changing planet interesting. It is constantly evolving and changing. We welcome your comments and additions.

3.9 - 4.4 Billion years ago - The Late Heavy Bombardment

Violent pelting of the earth by massive asteroids the size of Ireland was thought to have melted the Earths crust and vaporized any life on the planet. However, scientists now believe that much of the Earths crust and the microbes living on it could have survived and even thrived. Hydrothermal vents below the surface of the Earth may have offered sanctuaries for certain heat loving microbes, and may have even provided a kind of incubator for life. This opens up the possibility that life emerged as far back as 4.4 billion years ago, about the time the first oceans on the earth formed.

2.2 Billlon Years Ago - A Catastrophic Geologic Event - The oxygenation of the Earths Atmosphere

The mighty microbes

Human-caused global warming is the latest example of life altering Earth, but it is not the most dramatic. Humans "are having a strong effect on global geochemical cycles, but it does not compare at all to the advent of oxygenic photosynthesis," said Katrina Edwards, a geo-microbiologist at the University of Southern California (USC). "That was a catastrophic environmental change that occurred before 2.2 billion years ago [which] wreaked its full wrath on the Earth system", the oxygenation of Earth's early atmosphere by ancient microbes as they began to harness the power of sunlight through photosynthesis.

On land, microbes, and a form of bacteria called cyanobacteria, help keep soil in place and suppress dust. The microbes anchored soil to the ground; this created habitats for land plants to evolve and eventually for us to evolve. "They literally created Earth in a sense," Belnap said.

The mighty microbes also triggered sudden climatic shifts similar to what humans are doing now. Recent studies suggest that the proliferation of cyanobacteria 2.3 billion years ago led to a sudden ice age and the creation of a "Snowball Earth."

As they carry out photosynthesis, cyanobacteria break apart water and release oxygen as a waste product. Oxygen is one of the most reactive elements around, and its release into the atmosphere in large amounts destroyed methane, a greenhouse gas that absorbed the sun's energy and helped keep our planet warm.

Some scientists think the disappearance of this methane blanket plunged the planet into a cold spell so severe that Earth's equator was covered by a mile-thick layer of ice.

Earth might still be frozen today if not for the appearance of new life forms. As organisms evolved, many developed the ability to breathe oxygen. In the process, they exhaled another greenhouse gas, carbon dioxide, which eventually thawed out the world. That was the first biologically triggered ice age, but others followed, said Richard Kopp, a Caltech researcher who helped piece together the Snowball Earth scenario.

When trees first appeared about 380 million years ago, they also disturbed Earth's atmospheric equilibrium. Unlike animals, plants breathe in carbon dioxide and expel oxygen. Trees transform some of that atmospheric carbon into lignin-the major constituent of wood and one of the most abundant proteins on the planet. Lignin is resistant to decay, so when a tree dies, much of its carbon becomes buried instead of released back into the atmosphere as carbon dioxide. Less carbon dioxide in the atmosphere thins the blanket of gases that keeps Earth warm, and that cooling effect can trigger global cooling, possibly even an ice age.

Trees also affected the global carbon cycle in another indirect way. As they tunnel through the ground, tree roots break down silicate rocks into sediment and soil. Silicate rock contains large amounts of calcium and magnesium. When these elements are exposed to air, they react with atmospheric carbon dioxide to form calcium carbonate and magnesium carbonate, compounds that are widespread on Earth.

Though it might seem as if humans are mere fleas along for a ride on the back of an immense animal called Earth, our intelligence, technology and sheer numbers mean our species packs a punch that can shake the world in wild ways. While we are not the first species to drastically alter our planet, our influence is unique in a number of ways, scientists say.

For one thing, humans have developed large-scale industry, said Spencer Weart, a science historian at the American Institute of Physics. "We are capable of mobilizing things beyond our own biology," Weart said. "I emit a certain amount of carbon dioxide, but my automobile emits far more." Another is the rate at which humans are warming Earth. "Humans are the most common large animal to ever walk the planet," said Kirk Johnson, a chief curator at the Denver Museum of Nature & Science. "Population, plus brain power and technology, is a potent combination and the result is that humans are effecting change at very high rates."

Belnap agrees. "I don't think we've fundamentally changed any process. We've just cranked up the speed," she said. "We haven't introduced anything new. We've just changed how fast or slow it happens, and mostly fast."

But no matter how high humans cause the mercury to rise and how much damage we do to the planet, Earth and life will survive, scientists say. It just might no longer be in the form we prefer or the form that allows us to thrive.

"What we need to be thinking of as humans causing changes to the Earth system is what the consequences will be to us human beings," said Edwards, the USC geo-microbiologist. "The Earth could care less. We will be recorded as a minor perturbation in the Earth system. The Earth will go on. The question is: Will we?"

250,000,000 Years Ago Siberian Traps


The Siberian Traps were the largest volcanic eruption in Earth history and they occured right at the same time as the largest extinction event in Earth history. The massive volcanic eruptions and lava flows lasted at full intensity for about a million years. It is estimated that approximately 95% of all species were wiped out.

The Siberian Traps are a large igneous province centered around the siberian city of Tura and also encompass Yakutsk, Noril'sk and Irkutsk (see map above). Present coverage is just under 2 million square kilometres which is an area greater than that of Europe. Estimates of the original volume of the traps range from 1 million cubic km up to 4 million cubic km.

The real power of the Siberian Traps was the climate altering potential by the emission of ash and gases. The Siberian Traps is recognised as having a large proportion of pyroclastic deposits relative to other flood basalts. This indicates an explosive nature with much ash and gases being pumped into the atmosphere. All of this ash and gas has two main effects that, even though they are opposite to each other, act on differing timescales.

Initially sulfur aerosols and volcanic ash envelop the earths atmosphere blocking out sunlight and sending surface temperatures plunging . Ash and sulphur aerosols can remain in the upper atmosphere for 100's to 1000's of years which would be enough to cause a significant glaciation. At the end of the Permian period the biggest ever drop in sea level in history occurred. Two scientists named Holser and Magaritz in 1987 proposed that such a marine regression could be caused by a large scale glaciation.

The second major effect is the emission of greenhouse gases such as CO2, methane and also water vapour. Green house gases warm the climate by allowing sunlight to pass through, heat reflected by the Earth itself cannot penetrate the atmosphere so is retained. Greenhouse gases stay in the atmosphere much longer so their climate changing effects can last for millions of years.

The largest eruption of the 20th century, Mt Pinatubo is tiny compared to the Siberian Traps but caused a 0.5 degree drop in global temps the year after it erupted. The largest eruption in historic memory occured on Iceland in 1783-84 spewing out 12 cubic km of lava onto the island (the Siberian Traps erupted about 3 million cu km). The poisonous gases given out are recorded as killing most of the islands crops and foliage and lowering global temps by about 1 degree. If events this size can affect temperatures and large areas then the effects of a large scale flood basalt are incomprehensible.




65,000,000 Years Ago - A Meteorite Collided Into Earth

A giant asteroid, approximatly six-mile-in-diameter is thought to have hit Chicxulub in the Yucatan off the coast of Mexico 65 million years ago. The collision incinerated all the large dinosaurs that were alive at the time in only a few hours, and only those organisms already sheltered in burrows or in water were left alive.

"The kinetic energy of the ejected matter would have dissipated as heat in the upper atmosphere during re-entry, enough heat to make the normally blue sky turn red-hot for hours," said Robertson. Scientists have speculated for more than a decade that the entire surface of the Earth below would have been baked by the equivalent of a global oven set on broil.

The evidence of terrestrial ruin is compelling, said Robertson, noting that tiny spheres of melted rock are found in the Cretaceous-Tertiary, or KT, boundary around the globe. The spheres in the clay are remnants of the rocky masses that were vaporized and ejected into sub-orbital trajectories by the impact.

A nearly worldwide clay layer laced with soot and extra-terrestrial iridium also records the impact and global firestorm that followed the impact.

The spheres, the heat pulse and the soot all have been known for some time, but their implications for survival of organisms on land have not been explained well, said Robertson. Many scientists have been curious about how any animal species such as primitive birds, mammals and amphibians managed to survive the global disaster that killed off all the existing dinosaurs.

Robertson and colleagues have provided a new hypothesis for the differential pattern of survival among land vertebrates at the end of the Cretaceous. They have focused on the question of which groups of vertebrates were likely to have been sheltered underground or underwater at the time of the impact.

Their answer closely matches the observed patterns of survival. Pterosaurs and non-avian dinosaurs had no obvious adaptations for burrowing or swimming and became extinct. In contrast, the vertebrates that could burrow in holes or shelter in water -- mammals, birds, crocodilians, snakes, lizards, turtles and amphibians -- for the most part survived.

Terrestrial vertebrates that survived also were exposed to the secondary effects of a radically altered, inhospitable environment.