Most scientists think that the Sun and all of the planets in the Solar System formed at the same time, from a huge rotating gas cloud known as the Solar Nebula. This idea is called the Solar Nebula hypothesis. The solar nebula contained hydrogen and helium atoms from the Big Bang, tiny, dust grains, matter ejected from dead stars. The idea that the Earth was originally part of a giant gas cloud is not a new one. In 1755, Immanuel Kant suggested that the stars and planets came from a giant, whirling cloud of gas and dust.

Almost 5 billion years ago, the solar nebula began to collapse inward and to rotate more quickly. An external event, such as supernova, may have triggered this collapse. Eventually, the nebula flattened into a disk with a big lump of material in the center – the Protosun. Astronomers have found similar disks around other stars.

As the nebula contracted and gravitational energy became thermal energy, and the inner part of the nebula became very hot. Here grains of dust broke up into molecules and highly energized atomic particles.

Beyond what is now the orbit of Mars, temperatures were very low. Here frozen water, …

The image of someone casually walking across a tract of sand and suddenly finding themselves sinking deep into the Earth is something that many of us have witnessed on film or TV.  As the protagonist’s body begins to disappear and they scream for help,  we realize that they have unwittingly fallen into quicksand.

What is quicksand?  Dramatic portrayals of quicksand victims make it seem as though quicksand is a living entity that consciously grabs unwary travelers and attempts to carry them to their doom within the Earth’s bowels. In fact, quicksand is simply sand or soil that has been shaken up and saturated with water, usually from an underground spring. Quicksand can also form when  the tide moves up onto a beach or when an earthquake shakes up underground water and sand.

How to Escape Quicksand

If you leave quicksand alone, it will thicken again. Some types of quicksand are more watery than others.  Quicksand with a lower water content will become very viscous when it thickens.  Trying to pull your leg out of it would be like trying to pull your leg out of a giant vat of molasses or a tub of wet concrete.

Although people are often …

Limestone is a sedimentary rock that is made mostly of calcium carbonate in the form of the mineral calcite. It is unusual in that is often made from living matter, such as seashells and coral skeletons. Coal is another sedimentary rock made from organic matter.

If you put limestone in pure water, nothing will happen because limestone is insoluble in water.

However, when carbon dioxide from the air or from organic material dissolves in water, it forms carbonic acid. As this acidic water runs through cracks in limestone, the carbonic acid will react with the limestone to from calcium bicarbonate, which does dissolve.

As time goes by, in a process known as “chemical weathering”, the limestone will wear down. Weathering changes the shape of the limestone, forming some of the most spectacular landscapes on Earth.

Karst Landscapes

Landscapes formed by the chemical weathering of limestone or other rocks, such as gypsum, are known as Karst landscapes. . They often have very dry surfaces because water percolates through the limestone very easily. Plants grow only in hollows, where there is moist clay.

Karst landscapes are full of caves, sinkholes and underground streams.

Water that seeps in cracks in the landscape breaks …