Planet Earth and Its Environment A 5000-million year Journey

Part of the Evolution of Australian Biota ModuleBiology in Focus, Preliminary CourseGlenda Childrawi and Stephanie Hollis

Life on EarthTopic 2: Evidence for the origin of lifeDOT POINTIdentify the relationship between the conditions on early Earth and the origin of organic molecules

IntroductionThe approximate age of the Earth, based on geologic, magnetic, radiographic and palaeontological studies, is 4.5 billion years. During the Hadean eon (4.5-3.8bya) was the formation of the Earth. activistpost.com

Introduction 4 billion years ago the Earth was a very different place than it is today. The sun was only 70% of its present strength, Earth was spinning much faster and day was only 18 hours long and there was no free oxygen in the atmosphere How was anything to survive on such an inhospitable planet?

IntroductionWe know Earth transformed from a gaseous cloud into a solid body. The heavier molten elements, like iron, sank down to become the core. The lighter elements, like silica, rose to the surface and formed the crust.

But how did we get our atmosphere? flickrhivemind.net

IntroductionIntense heat and pressure, due to the extreme forces of gravity, below the surface cause the material to remain in a molten state. We know that hot material rises (think of boiling water), and so does this molten material in the centre of the Earth. physics.arizona.edu

IntroductionOnce this molten material reaches the surface we get volcanoes! These amazing geologic features not only bring to the surface fresh minerals and rock, they also bring gases trapped within the material.

It was these gases that formed the original atmosphere of our planet.en.wikipedia.org

Early Earths AtmosphereThe process of volcanoes releasing gases into our atmosphere is called outgassing and included:Water (HO)Methane (CH)Ammonia (NH)Hydrogen (H)Nitrogen (N)Carbon Dioxide (CO)

geology.com

Early Earths AtmosphereThe atmosphere was anoxic meaning it had no free Oxygen (O) as all the oxygen was bound within other compounds such as water and carbon dioxide. This meant that there was no ozone (O) layer exposing the Earths surface to ultraviolet radiation.howitworksdaily.com

Early Earths AtmosphereMost of the hydrogen gas escaped into space, as happens today, whereas the other gases accumulated and remained in the atmosphere.telegraph.co.uk

Forming the First Organic MoleculesEarly Earth provided an environment in which the production of organic carbon-containing molecules could have happened fairly easy. The energy for driving these reactions could have come from a number of sources which include:Sun (ultraviolet radiation)LightningHot springsVolcanoesRadioactivity in the crustMeteorite impactsenvironment.nationalgeographic.com

Forming the First Organic MoleculesIn Early stages of Earths formation, organic molecules would have most likely formed in the lower atmosphere or at the Earths surface. Well look at the stages of change thought to occur in the early Earth.spaceprime.com

Forming the First Organic MoleculesDense clouds formed in the steamy atmosphere. These clouds were formed of water from meteorites and hydrated minerals. These clouds then formed a reflective shield from the suns penetrating heatscientificamerican.com

Forming the First Organic MoleculesAbout 500 million years later, meteorite impacts declined due to this protective layer and the friction caused on entry. The Earth cooled and the temperature fell below 1000C, forming a stable rocky crust. amp.wpcamr.org

Forming the First Organic MoleculesThe release of gases from volcanoes increased air pressure in the atmosphere. When the temperatures cooled, this assisted in causing the immense clouds of water vapour to condense into liquid and fall as rain.zdnet.com

Forming the First Organic MoleculesRain would have washed organic molecules into lakes and ponds rich in dissolved minerals. This created an environment for reactions to occur which produced new organic molecules and compounds.

Forming the First Organic MoleculesCarbon Dioxide dissolves readily in water to form carbonic acid (HCO). It would have been flushed out of the atmosphere by rain and into the oceans where it reacted with calcium to form calcium carbonate (CaCO)carbon-based-ghg.blogspot.com

Forming the First Organic MoleculesAt first, the rain evaporated as it fell on the hot rock surface but the evaporation gradually cooled the crust until water could accumulate in the lower regions of the Earths surface forming oceans. The first rives were created where the water, dissolving and transporting minerals along the way, eventually ran back into the oceans.ibn-tv.com

Forming the First Organic MoleculesThe dissipation of heat into space cooled the Earth, causing crust fragments to become numerous enough to form a first thin, solid cover.norblog.typepad.com

Forming the First Organic MoleculesOver the next 3.5 billion years, the amount of carbon dioxide in the atmosphere was reduced as it became incorporated in rocks (limestone). The main gas remaining in the Earths atmosphere was nitrogen.onorbit.com

Forming the First Organic MoleculesThe composition of Earths atmosphere today is somewhat different to that proposed on early Earth. Today it consists of 78.1% nitrogen, 20.9% oxygen and 1% trace elements such as carbon dioxide, water vapour, methane, hydrogen and ozone.redorbit.com

Forming the First Organic MoleculesThere is much known about the composition and conditions of Early Earth, however there are a lot of unanswered questions. Scientists continue to search for more evidence reflecting the conditions of early Earth that may have existed when life began. futurity.org

Forming the First Organic MoleculesIf these conditions are known, then we may perhaps discover more about the building blocks from which life began.scribd.com

HomeworkNone again!