Sunday 14 June 2015

NATURE GAVE US LIFE : Evolution of plants on earth by nature

Prokaryotes are the organisms classified as Bacteria and Archaea, and are the most successful & abundant organisms on Earth. In fact they have been THE dominant group on earth since life appeared and for around 2000 million years were the only life form on earth. Prokaryotes as a group have the largest biomass on the planet e.g. in the oceans, prokaryotes make up 90% or greater than the total weight of living things; there may be 2.5 x 109 prokaryote cells in a gram of fertile soil. Prokaryotes are also the most ancient organisms on Earth: the earliest known fossil cells belong to a prokaryote, and come from rocks in Western Australia that date back 3500 million years. All prokaryotes are small cells that lack the complex internal structures, like mitochondria and chloroplasts, found in eukaryotic cells. Also, although prokaryotes possess DNA on a chromosome, it is not enclosed in a nucleus.

Because prokaryotes are largely invisible to the human eye we tend to forget about them. However, they contributed to the development of an oxygen-rich atmosphere early in Earth's history, and are essential to the processes of decomposition and nutrient cycling, a key role in all ecosystems. They also made a significant contribution to the evolution of the better-known, eukaryote, life forms.




Present-day prokaryotes may resemble early fossils, but they are modern organisms that have successfully adapted to modern environmental conditions. They are found in some of the most extreme environments on Earth, including Antarctica, the depths of the oceans and deep in rocks, round deep-sea vents, and in boiling thermal springs and are ever present in our human environments, including cities, homes and the human body.




The Cyanobacteria (blue-green algae) are a group of prokaryotes that are extremely important both ecologically (especially in global carbon and nitrogen cycles) and evolutionary terms. Stromatolites, which are formed by cyanobacteria, provide living and fossil evidence of cyanobacteria going back 2700 million years. Today stromatolites grow only in shallow, salty pools in hot, dry climates (e.g. Shark Bay in Western Australia), and their abundance in ancient rocks implies similar environmental conditions in those times. Stromatolites and other cyanobacteria were the main contributors to the marked increase in atmospheric oxygen concentrations that began around 2000 million years ago. Today, cyanobacteria are found everywhere - in marine, freshwater and terrestrial environments and as symbionts e.g. lichen - and contribute up to 50% of the atmosphere's oxygen.

DNA evidence suggests that the first eukaryotes (green plants) evolved from prokaryotes (through endosymbiotic events) between 2500 and 1000 million years ago. Fossils of eukaryotes that resemble living brown algae have been found in sedimentary rocks from China that are 1700 million years old, while possibly the oldest photosynthetic eukaryote, Grypania, comes from rocks 2100 million years old. Note that the diversity of modern algal groups, and particularly of their chloroplasts, suggests that these endosymbiotic events were not unusual. Modern algae comprise a range of organisms with very different structures but identical photosynthetic pigments. This suggests that very different host organisms have formed a symbiosis with the same photosynthetic cells. That is, the algal groups must have evolved through separate endosymbiotic events, and the group as a whole is identified on the basis of a similar level of structure, rather than on its evolutionary origins. Such groups, where the members have several different evolutionary origins, are described as polyphyletic.

Cyanobacteria have a close evolutionary relationship with eukaryotes. They have the same photosynthetic pigments as the chloroplasts of algae and land plants. Chloroplasts are the right size to be descended from bacteria, reproduce in the same manner, by binary fission, and have their own genome in the form of a single circular DNA molecule. The enzymes and transport systems found on the folded inner membranes of chloroplasts are similar to those found on the cell membranes of modern cyanobacteria, as are their ribosomes. These similarities between cyanobacteria and chloroplasts suggest an evolutionary link between the two, and can be explained by the theory of endosymbiosis.




For 1500 million years photosynthetic organisms remained in the sea. This is because, in the absence of a protective ozone layer, the land was bathed in lethal levels of UV radiation. Once atmospheric oxygen levels were high enough the ozone layer formed, meaning that it was possible for living things to venture onto the land. The seashore would have been enormously important in the colonisation of land. In this zone algae would have been exposed to fresh water running off the land (and would have colonised the freshwater habitat before making the move to terrestrial existence). They would also be exposed to an alternating wet and desiccating environment. Adaptations to survive drying out would have had strong survival value, and it is important to note that seaweeds are poikilohydric and able to withstand periods of desiccation.
The earliest evidence for the appearance of land plants, in the form of fossilised spores, comes from the Ordovician period (510 - 439 million years ago), a time when the global climate was mild and extensive shallow seas surrounded the low-lying continental masses. (These spores were probably produced by submerged plants that raised their sporangia above the water - wind dispersal would offer a means of colonising other bodies of water.) However, DNA-derived dates suggest an even earlier colonisation of the land, around 700 million years ago.

Thursday 11 June 2015

NATURE GAVE US LIFE : How oxygen formed by nature for evolution of life

We all know we can't live without oxygen, 400 million year ago oxygen is also formed by nature. But question arise how oxygen formed? Scientists agree that there’s oxygen from ocean plants in every breath we take. Most of this oxygen comes from tiny ocean plants – called phytoplankton – that live near the water’s surface and drift with the currents. Like all plants, they photosynthesize – that is, they use sunlight and carbon dioxide to make food. A byproduct of photosynthesis is oxygen.

Scientists believe that phytoplankton contribute between 50 to 85 percent of the oxygen in Earth’s atmosphere. They aren’t sure because it’s a tough thing to calculate. In the lab, scientists can determine how much oxygen is produced by a single phytoplankton cell. The hard part is figuring out the total number of these microscopic plants throughout Earth’s oceans. Phytoplankton wax and wane with the seasons. Phytoplankton blooms happen in spring when there’s more available light and nutrients.





And the density of phytoplankton varies. They sometimes float just at the surface. At other times and places they can be a hundred meters – about 100 yards – thick. By the way, by about 400 million years ago, scientists say, enough oxygen had accumulated in Earth’s atmosphere for the evolution of air-breathing land animals. But free oxygen by itself wasn’t enough. Another form of oxygen was also essential: the build-up of a special kind of oxygen at the top of Earth’s atmosphere. There, where three atoms of oxygen bonded together, ozone formed. This layer of ozone at the top of Earth’s atmosphere shields land organisms from harmful ultraviolet radiation from the sun.




So in this way nature created oxygen. Nature set the all perfect condition for the evolution of life

Tuesday 9 June 2015

NATURE GAVE US LIFE : Origins of life on earth

Now nature starts its main role to create a life on earth.Life on Earth has been changing at various rates since our common ancestor first appeared more than 3.5 billion years ago. After collision of earth with theia, earth start come its shape.Gravity pulled earth and earth comes in its spherical shape.The Earth's crust had cooled and the oceans had formed and conditions were more suitable for the formation of life. The first living organism formed from simple molecules present in the Earth's vast oceans between 3.8 and 3.5 billion years ago. This primitive life form is know as the common ancestor.As Earth began to take solid form, it had no free oxygen in its atmosphere. It was so hot that the water droplets in its atmosphere could not settle to form surface water or ice. Its first atmosphere was also so poisonous, comprised of helium and hydrogen, that nothing would have been able to survive. 



The common ancestor is the organism from which all life on Earth, living and extinct, descended .We know that life began at least 3.5 billion years ago, because that is the age of the oldest rocks with fossil evidence of life on earth.  These rocks are rare because subsequent geologic processes have reshaped the surface of our planet, often destroying older rocks while making new ones. Nonetheless, 3.5 billion year old rocks with fossils can be found in Africa and Australia.  They are usually a mix of solidified volcanic lavas and sedimentary cherts.  The fossils occur in sedimentary cherts..




Earth’s second atmosphere was formed mostly from the out gassing of such volatile compounds as water vapor, carbon monoxide, methane, ammonia, nitrogen, carbon dioxide, nitrogen, hydrochloric acid and sulfur produced by the constant volcanic eruptions that besieged the Earth. It had no free oxygen.
About 4.1 billion years ago, the Earth’s surface — or crust — began to cool and stabilize, creating the solid surface with its rocky terrain. Clouds formed as the Earth began to cool, producing enormous volumes of rainwater that formed the oceans. For the next 1.3 billion years (3.8 to 2.5 billion years ago), the Archean Period, first life began to appear and the world’s landmasses began to form. Earth’s initial life forms were bacteria, which could survive in the highly toxic atmosphere that existed during this time.


Nature nature made environment for the evolvement of life.