Water on the Earth and Species Evolution

yang+Ziyuan

Water is the source of life. The Earth is the only known planet so far in the solar system with living life. Where does its water come from？ What changes have the water on the Earth been through？ How does water nurture life in various forms？

Earth：

A miracle of coincidence

In the vast solar system， the Earth is the only planet where all things can grow vibrantly. Earth creates diverse biological species and nurtures high wisdom human beings and supports the building of a highly civilized human society. We owe all these to the advantageous conditions of the Earth. The Earth locates at a favorable position， neither close to nor far away from the sun. The size of the Earth is also appropriate， neither large nor small. Besides， the Earth rotates calmly and stably.

It has a rocky crust and 72% of its surface is covered by water， providing a broad space for the survival and reproduction of life.

Ocean tides provides driving force for creatures to migrate.

The Earth is surrounded by magnetosphere， ionosphere and the ozone layer， its life being protected by those layers from cosmic radiation damage.

The atmosphere of the Earth was originally made up of toxic gas from the volcano eruption. It gradually evolved into carbon dioxide atmosphere and further evolved into nitrogen-oxygen atmosphere， fueling the reproduction of life. The water body （oceans， lakes and rivers）of the Earth's surface evolved gradually from containing strong acid to weak acid and then to neutral water which is beneficial to the habitat and evolution of creatures.

In the long path of the Earth's evolution， the coordinated evolution of atmosphere， water and the biological species， presents a perfect picture of harmony. The origin and growth of a wide range of biological species and intelligent creatures on the Earth is the result of long-term evolution of the Earth， a coincidence and a miracle of the universe！

Where does the water come from：

Origin of water on the Earth

Water plays an important role in the evolution of life. So where does the water on the Earth come from？ Scientists have carried out extensive researches and put forward various hypothesis.

At the moment， there are two major hypothesis regarding the origin of water： one believes that at the early stage of the Earth formation， the interior mantle material of the Earth melts massively. After extensive and long-term volcanic eruption， lava flows all over the surface of the Earth， releasing a large amount of volatile matter mainly composed of water vapor. Those volatile matters cools down forming ground water. Therefore， the Earth's water comes from the Earth's mantle degassing process； Another hypothesis says the water originates from large numbers of comets that clash at the Earth.

The Earth debasing and releasing steams， which condenses into water on the Earth.

At the early stage of formation of solar system， magmatic ocean event outbreaks on the Earth and other terrestrial planets， including the Moon. The interior material of the Earth （mainly mantle） melts， through extensive volcanic eruption. When the lava covers massive areas， a large number of gas volatile is released from the Earth. Volume of lava flow changes as time passes by， which shows that volcanic activity weakened gradually. In accordance to the modeling calculation results， the volatile gas amount erupted from early activities on the Earth is estimated to be around 1.78 million trillion tons.

Researches all over the world on all kinds of volcanic gas reveals that the main volatile gas from interior degassing process of the Earth is water vapor， accounting for 70% ～ 90% of the total， followed by carbon dioxide （CO2）， carbon monoxide （CO）， sulfur dioxide （SO2）， hydrogen sulfide （H2S）， hydroelectric acid （HCl）， ammonia （NH3）， ammonium chloride （NH4Cl）， chlorine （Cl2）， nitrogen （N2） and sulfur （S）， etc. An average of up to 1.42 million trillion tons of water vapor （become water after cooling， and accumulate on the Earth surface） was released from interior degassing process of the Earth. This equals to the volume of water on the Earth. Systematic measurement and research on the hydrogen and oxygen isotopic compositions of all kinds of water and oxygen isotopic composition of carbon dioxide prove that water on the Earth is from the degassing process of the Earth's mantle.

Hypothesis 2：

Comets hit the Earth and water originates from comets

Another hypothesis thinks that the water is brought by the comet hitting the Earth. Is this true？ We need scientific methods to test and verify. Nucleus of a comet is made up of frozen water and dust material. If the water on the Earth is from comets， according to astronomers estimates， we need at least 20 million comets with medium or above size to fill the oceans. The evolutionary history of the solar system can hardly provide scientific basis.

By studying the homo-logy of water， scientists often measure the hydrogen isotopic composition of water or ice （deuterium/hydrogen， or D/H）. the Earth D/H ratio of sea water is 1.56 x 10-4， which is less than half the D/H ratio of comets compared with comet Halley， Hyakutake and comet Hale – Bopp. In August 2014， the European space agency's Rosetta spacecraft arrived at 67P/ Comet Churyumov–Gerasimenko. Rosetta orbiter released philae lander on the surface of 67P of the nucleus， and determined D/H ratio of hydrogen isotope of the Comet Ice is 5.3 x 10-4， 3 times of that of the Earth water. These data suggest that water on comets and the Earth is not homogeneous， therefore comet water is not the source of the Earth's water.

The development of ocean， atmosphere and biological evolution

At the early stage of the Earth formation， ocean， atmosphere and biological evolution experienced a very long process of coordination and development. Various factors influenced each other， changed gradually and eventually formed a vibrant and suitable planet for life.

The development of ocean and atmosphere

At the early stage of formation of solar system， the Earth and other terrestrial planets all had primeval atmosphere. The Sun was in T variable phase when strong solar wind drove all primeval atmosphere of the planet away to the giants regions farther from the Sun. Nowadays the atmosphere of the Earth and other planets is secondary atmosphere. The Earth's atmosphere and water body had undergone an extremely complex process of coordination and evolution， thus forming the nitrogen - oxygen atmosphere and the ocean water of today.

After its formation， the Earth released through strong volcanic activities large amounts of water vapor （H2O）， sulfur dioxide （SO2）， hydrogen sulfide （H2S）， hydroelectric acid （HCl）， chlorine （Cl2）， nitrogen （N2）， sulfur （S） of steam， ammonia （NH3）， ammonium chloride （NH4Cl） and other volatile， forming the primeval atmosphere. A lot of strong volatile acid dissolved in water， making the Sea water strongly acidic. 2.5 billion years ago， the Earth's atmosphere was still predominantly the product of volcanic eruption， forming the volcanic atmosphere； while sea water evolved into chloride water， with pH value less than or equal to 4. Around 2 billion years ago， ocean evolved into a chloride-carbonate water body， the pH of which was 4～5. With large amounts of carbon dioxide （CO2）， the atmosphere gradually formed carbon dioxide atmosphere with CO2 as the main component. With the increase of water pH value， higher solubility of CO2， a large number of carbonate precipitation appeared. In Paleozoic， the emergence of a large number of plants and animals in particular， caused the decrease of partial pressure of CO2 and the rapidly rise of oxygen （O2） in the atmosphere， gradually evolving into today's nitrogen-oxygen atmosphere. the Earth water evolved into chloride- carbonate-sulfate water body， and later into today's neutral and slightly alkaline water body. The development of the Earth's atmosphere and water body demonstrate features of synthetic evolution.

Development of evolution of water bodies and creatures on the Earth

the Earth formed about 4.6 billion years ago. Around 3.8 billion years ago， in the dense primeval volcanic atmosphere， prokaryotes were born in strong acidic water. Filamentous bacteria fossils in the group Guevara Ulna with a history of 3.5 billion years found in Australia， represents the earliest fossils with cellular structure on the Earth.

The earliest heterotrophic prokaryotic bacteria appeared and continuously differentiated and developed in the chloride sea water. Eventually， autotrophic prokaryotic cyanobacteria appeared， being capable of photosynthesis and synthesis of organic nutrients from inorganic substances. Cyanobacteria， the earliest oxygen-releasing creatures on the Earth， increase oxygen concentration of the primeval atmosphere， providing a favorable living environment for aerobic creatures. Intact bacteria and algae fossils dating back to 20 billion years ago were discovered in Gan Flynn group， Canada.

As eukaryotes emerging in chloride-carbonate-sulphate water， animals and plants began to differentiate and develop. Green plants （eukaryotic and prokaryotic cyanobacteria）， making food through chlorophyll photosynthesis， is the producer of nature； bacteria and fungi are decomposers； while animals are consumers in nature. The earliest animal fossils in ground history could date back to 700 million ～ 600 million years ago， and it is Ediacaran fauna found in Australia， among which coelenterate， such as watery parent class， sea gill class， annelids and small amount of arthropods， constitutes the majority.

600 million years ago， in the early Paleozoic period， there were once the " marine algae era" and "marine invertebrates era". Chengjiang fauna which could date back 570 million years ago was discovered in Yunnan China， mainly composed of jellyfish， trilobites， gold arm insects， non- trilobite arthropods， demodex animals， sponges ， brachiopods no hinges， soft tongue snails and algae etc.，. which represents the world 's first well preserved multi-category software fauna. With the Nitrogen - oxygen atmosphere and sea environment similar as the one of today， 500 million years ago， in ground history emerged the earliest crust with small calcareous shell fauna， including soft tongue snail， veneer， gastropods， brachiopods and so on， which was related to the pH value （close to 7） and the Sea water rich of calcium.

The favorable environment is conducive to the continued development of marine invertebrates， therefore stromatoporoids， bryozoans， and the like appeared one after another and graptolites， brachiopods， nautilus， etc had significant differentiation. Corals， stromatoporoids and bryozoans together consist important reef animals in warm shallow water.

570 million to 2.3 billion years ago， the atmosphere and the ocean water were already similar to the current situation. Creatures entered a prosperous period ever， with unprecedented growth in terms of number and population. The years dating back from 230 million to 67 million witnessed the era of gymnosperms and reptiles era. The years since 6700 of the Cenozoic era came the era of angiosperms and mammals. A roughly 300 million years ago， human beings appeared on the Earth.

The formation and coordination and development of the Earth's atmosphere and oceans， the origins and growth of various biological species and intelligent creatures on the Earth demonstrate a perfect picture of harmony. It is the result of long-term evolution of the Earth， created by coincidence and is a miracle of the universe！ Should we cherish and protect Earth， our mother， for the survival and reproduction of life .