How The Earth was formed Moray Coast U3A How The Earth was formed

Scientists believe that the Earth didn’t always exist Moray Coast U3A Scientists believe that the Earth didn’t always exist Our Earth was formed at some point in the distant past. A time will come when it will no longer support life as we know it.

Moray Coast U3A The Earth in space

Moray Coast U3A Note how thin the atmosphere is

Moray Coast U3A Earthrise from lunar orbit

Our solar system is estimated to be about 4.6 billion years old. Moray Coast U3A Our solar system is estimated to be about 4.6 billion years old. That’s 4,600,000,000 years old. That’s 4.6 x 109 years old in standard form or scientific notation. How do we know this? The age is estimated from a study of the radioactive decay of unstable isotopes. Isotopes are different atoms of the same element having the same number of protons but different numbers of neutrons.

The simplest element, hydrogen, has three isotopes. Moray Coast U3A The simplest element, hydrogen, has three isotopes. Most hydrogen atoms have one proton only in their nucleus. A few hydrogen atoms have one proton and one neutron in their nucleus. Even fewer hydrogen atoms have one proton and two neutrons in their nucleus. These atoms are unstable and radioactive. The half life of this atom is 12.3 years but other elements have unstable isotopes that last far longer. The most common isotope of uranium has a half life of 4.4683×109 years, about the age of the Earth.

Moray Coast U3A The radioactivity never gets to zero but becomes insignificant with time The half life ( t½ ) for 238U is 4.4683×109 years

Moray Coast U3A Minerals which were thought to contain pure, 100%, uranium 238 when formed now contain only about 50% of this type of uranium atoms. The rest has decayed into daughter isotopes. This tells us that the age of the Earth is about the same as the half-life of uranium, about 4.4683×109 years. Careful measurements of uranium and other radioactive elements such as thorium gives the age of the Earth as about 4.6 x 109 years old. There is a small margin of error in these measurements but this can be calculated. Eg:- 4.6 x 109 ± 104 years

Moray Coast U3A Our solar system consists of the sun, the inner planets, the outer planets, all the moons, all the asteroids, the comets and debris such as the small fragments that form micro-meteorites.

Moray Coast U3A The formation and evolution of the Solar System began about 4.6 billion years ago with the gravitational collapse of a small part of a giant molecular cloud. 

Moray Coast U3A Some of the molecular cloud was probably left over from the big bang but other material was ejected from the outer shells of novas and supernovas, the death throws of dying stars.

Those areas of higher density attract more material to them. Moray Coast U3A The density of these gas clouds are not uniform. There are areas of slightly higher density and areas of slightly lower density. Those areas of higher density attract more material to them. As more matter slowly “falls” into the centre of higher density areas these areas start to spin. The gas cloud evolves into a series of protoplanetary disks.

Moray Coast U3A Most of the collapsing mass of gas is pulled to the centre, by gravity, eventually forming a star. As the gas cloud collapsed under gravity it starts to spin and form a disk with a bulge at the centre. The flattened part of this protoplanetary disk would eventually become the planets, moons, asteroids, and other small bodies of a planetary system like our Solar System.

Modern research confirms this hypothesis. Moray Coast U3A This is not a modern theory but was first put forward in the 18th century by Emanuel Swedenborg, Immanuel Kant, and Pierre-Simon Laplace. Modern research confirms this hypothesis. Photographs from the Hubble Space Telescope actually show protoplanetary discs being formed.

Moray Coast U3A Protoplanetary disks forming in the constellation of Orion

Moray Coast U3A An artists impression of the protoplanetary disk that formed our early Solar System The sun has just burst into life There is still a great deal of dust and debris in the protoplanetary disk

Moray Coast U3A This was a slow process Mathematical models show that denser material would accumulate towards the centre of the disk. The inner planets, Mercury, Venus, Earth and Mars are much denser than the outer planets. Less dense material tended to end up in the outer reaches of the protoplanetary disk. Jupiter is a huge planet with a huge gravitational field but if one could find a sufficiently large ocean it would float. Jupiter is less dense than water!

The early solar system was chaotic. Moray Coast U3A The early solar system was chaotic. There was a period of intense bombardment as asteroid sized chunks of material would slam into the proto-planets.

This bombardment produced enough heat to melt most materials. Moray Coast U3A This bombardment produced enough heat to melt most materials. On each planet the denser material would sink to the centre which explains why the Earth’s core is almost certainly made up of mainly iron with some nickel. The planet slowly cooled to form a crust.

The Earth cooled slowly Moray Coast U3A The Earth cooled slowly

Moray Coast U3A Where all the water on our Earth came from is not completely understood. Much came from comets and asteroids during a period of intense bombardment. The early Earth was subjected to considerable bombardment until its gravitational field had “swept” the space of its orbit “clean”

Moray Coast U3A Early bombardment Late heavy bombardment

Moray Coast U3A Early bombardment The Hadean Aeon

Moray Coast U3A The Earth slowly cools over tens of millions of years and is under regular bombardment from comets and asteroids.

Late heavy bombardment Moray Coast U3A Late heavy bombardment

Comets may not be the only source of water. Moray Coast U3A Comets contain large quantities of water, as ice, and late bombardment by comets must have made a major contribution to the water in our oceans. Comets may not be the only source of water.

One of the main gases given off by volcanoes is water vapour, (steam). Moray Coast U3A Evidence suggests that some water was present at the time the Earth formed. Today there is a considerable quantity of water in the mantle which is dissolved in molten magma under intense pressure. One of the main gases given off by volcanoes is water vapour, (steam). Clearly oceans could not form until the surface of the earth was cool enough to condense liquid water at the surface.

Our Moon – How did it form? Moray Coast U3A Our Moon – How did it form?

Moray Coast U3A Most scientists now believe that our Moon formed after an enormous collision between the early Earth and a Mars sized planet which has now been called Theia The cataclysmic collision would have vaporised most of the early Earth

Moray Coast U3A There is a great deal of technical evidence to support this theory.

Much of the evidence has been obtained from the study of moon rocks. Moray Coast U3A Much of the evidence has been obtained from the study of moon rocks. Most of the rocks and minerals on the Moon are like those on Earth suggesting a similar origin. Even the isotopic composition is the same.

Moray Coast U3A The theory that the Moon was a separate entity orbiting the sun that was somehow “captured” by the Earth’s gravitational field has now been ruled out by scientists who work in the field.

To find out more we need to go back to the moon. Moray Coast U3A To find out more we need to go back to the moon.

We could find out much more by exploring Mars and other planets. Moray Coast U3A We could find out much more by exploring Mars and other planets.

Moray Coast U3A Any questions? The End