Why Are Mountains High and Oceans Deep?

by Dr. Andrew A. Snelling on October 1, 2020
Featured in Answers Magazine
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The high and deep landscapes of earth give insight into the Creator’s wise design of rocks.

From the North Carolina Outer Banks to Castaway Island, Fiji, beaches draw millions of vacationers eager to dig their toes into the sand and splash in the depths of the blue waters.

At the same time, millions of other travelers hike trails in Tennessee’s Smoky Mountains or ski the slopes in British Columbia.

But oceans and mountains are more than perfect vacation spots. Both are extremely important for making our planet uniquely suitable for life to flourish. Water that evaporates from the ocean’s surface forms clouds, and winds carry those clouds toward land. There the clouds rise into the mountains, where they drop their water as rain and snow. The water then drains down to rivers and back to the oceans (Ecclesiastes 1:7).

But what makes mountains so high and oceans so deep? These perfectly designed geographies didn’t come into being by random processes as evolutionists claim. They believe that billions of years after the supposed big bang, planet earth was randomly flung out from the supposed solar nebula that became the sun. But that accidental occurrence could never explain how the atoms of the different elements in rocks perfectly evolved and combined to form the minerals in rocks.

The more logical explanation is that during creation week God formed the original mountains and ocean floors from different kinds of rocks called granites and basalts, respectively, each created to fulfill a specific purpose. Then during the flood judgment when he totally destroyed the earth’s surface, he caused today’s mountains and ocean floors to form from more granites and basalts. Studying these rocks provides further insight into the Creator’s wisdom in making our planet a habitable home.

Getting to the Bottom of It

Not too long ago, glowing lava streams eerily inched across the green Hawaiian landscape, consuming everything in their path. When that lava cooled, it formed the black volcanic rock called basalt, commonly found across the earth’s surface. Normally, you’ll need a magnifying glass or microscope to see the tiny interlocking grains that compose this rock. Basalt usually appears uniformly black, but sometimes you can spot tiny crystals in it.

Underneath a thin layer of loose sediments, the deep ocean floor consists of basalt.

In contrast, the continents and their mountains are made of granite and other rocks which together average the same composition as granite. Granites crystallize and cool from melted rock called magma. Unlike basalt, granite is formed deep under the ground. In the Yosemite area of California, granites are all that we see where erosion has exposed them at the earth’s surface.

Granites are composed of large crystals in an array of various colors (white, pink, glassy, and black), easily seen with the naked eye.

Because basalt is denser (having more and heavier atoms in the same space) and heavier than granite, the ocean floor sinks relative to the less-dense granitic continents, forming basins in which the ocean waters have collected.

So why are basalts and granites so dissimilar? According to how and where they formed, they were composed differently because they consist of different minerals.

Deep in the Earth

Basalts and granites are called igneous rocks. Igneous comes from the Latin word ignis for “fire.” Igneous rocks crystallize and cool from melted or molten rock, which can reach temperatures of 1,300–2,200°F (650–1,200°C).

Under the ground the molten rock is called magma, but when it erupts at the earth’s surface, it is called lava. Igneous rocks that crystallize and cool under the ground are called plutonic rocks, named after Pluto, the mythological god of the underworld. Granites are the prime example of plutonic rocks.

On the other hand, when lavas erupt from volcanoes, the igneous rocks that crystallize and cool on the earth’s surface are called volcanic rocks. Basalts are the best-known example of volcanic rocks.

The magmas which crystallize granites and basalts have different compositions, primarily due to the differing amounts of silica (SiO2) in them. Granites usually have 65–70% silica, whereas basalts have only 45–50%.

When granitic and basaltic magmas cool, different minerals crystallize. With so much silica in them, granites always contain the mineral quartz (SiO2), which is essentially the same composition as window glass—and it looks like it. Granites often contain other minerals, such as pink potassium feldspar, creamy white plagioclase feldspar, black or white mica, and/or black amphibole.

On the other hand, basalts often contain tiny crystals of the green mineral olivine, dark pyroxene, and gray plagioclase feldspar.

Because of their different compositions, basalts and granites originate inside the earth from different sources with those different compositions.

The Earth’s Well-Designed Internal Structure

Internal Structure

The inset shows the earth’s central inner core surrounded by concentric outer core, mantle, and crust layers. There are two types of crust, the earth’s outer “skin,” as shown in the main diagram.

Because basalt is denser than granite (more and heavier atoms in the same space), basalt is heavier. So the ocean floor (oceanic crust) sinks relative to the less-dense granitic continents (continental crust). Thus, the sunken ocean floor has formed basins in which the ocean waters have collected. The accumulation of many rock layers on the continents during the flood also makes the continents thicker so that they stand up higher. The continents are thickest and highest where there are mountains.

Where Do Basalts and Granites Come From?

God created the earth to have different layers. At the center of the earth is the core (layer 1), which consists of iron with some nickel. Surrounding the core is the 1,800-mile (2,870 km) thick rocky mantle (layer 2).

On top of the mantle is the earth’s outer “skin” called the crust (layer 3), which varies in thickness between about 3 and 45 miles (5–70 km). The crust is divided into oceanic crust and continental crust, and, as the names imply, makes up the ocean floors and continents.

The temperatures at the upper mantle’s depths (around 2,200°F [1,200°C]) are capable of melting some of the mantle’s minerals. The resulting mantle melt is basaltic magma, because the mantle there is similar in composition to basalt. Because the basaltic magma is less dense than the surrounding mantle and is under pressure, it is squeezed up through any fractures or conduits into the crust and sometimes reaches the earth’s surface through volcanoes.

In contrast to what happens in the upper mantle, deep within the continental crust (where the temperatures can reach 1,300°F [650°C]) melting can occur where the pressures assist to also produce magma. But because the continental crust is of a different composition to the mantle, the melting produces a granitic magma. Again, the granitic magma is less dense than the surrounding solid crustal rocks and is under pressure, so it rises up through any factures or conduits higher in the crust. Often it stops rising at about 1–3 miles (1.6–5 km) under the ground where it pools, cools, and crystallizes, only sometimes erupting at the earth’s surface.

So what has all this got to do with how today’s mountains and oceans formed?

Factoring In the Flood

In the beginning, God created the various igneous rocks to make up the original ocean floors and the supercontinent. But as the “fountains of the great deep” broke open during the global flood cataclysm, the earth’s crust broke into plates. Through those huge cracks across the original ocean floors, magma rose from the melting upper mantle to “push aside” the old ocean floors and form today’s new basalt ocean floors.

Catastrophic movements of all the crustal plates caused subduction, old ocean floor plates being shoved under the edges of continental plates. This caused the upper mantle and deep continental crust to melt, forming more magmas, which produced many volcanoes with their varying lavas (see sidebar below).

Why Do Igneous Rocks Have Different Compositions?

The plutonic (cooled underground) equivalent of the volcanic (surface) rock basalt is called a gabbro. So-called “black granite” is actually gabbro. And “green granite” is peridotite, due to its predominant green olivine.

When a basaltic magma forces its way up through the continental crust, it can sometimes melt some of the crust. Pieces of continental rocks can also get consumed and included into the basaltic magma. This changes the magma composition, so when it cools underground or erupts, it produces plutonic or volcanic rocks of different compositions from basalt.

There is a whole continuum of final magma and lava compositions and, therefore, the plutonic and volcanic rocks they produce. Some lava compositions can cause explosive volcanic eruptions.

Varieties exist even within these named rock types. For example, the varieties of granites used for everything from impressive rock edifices to statues to modern kitchen countertops are due to the different proportions of minerals in them, resulting from the different compositions of the melted source rocks.

The lavas called andesites are so named because they are predominantly erupted from volcanoes in the South American Andes Mountains. The basaltic magma coming from the upper mantle below the western edge of South America got contaminated as it rose to the surface. Because its composition changed, it erupted as andesite.

Similarly, in the US Pacific Northwest, the mantle that melted beneath that region produced basaltic magmas that got heavily contaminated by continental rocks and have erupted as dacite lavas, such as those at Mount St. Helens.

Also, many sedimentary rock layers were deposited by the flood waters on the new continental plates. As these continental plates then collided, their edges buckled, thickening the sedimentary layers that produced mountains and sometimes melting those layers at depths that produced granites.

So out of the heat, pressure, and melting during the flood’s upheaval about 4,300 years ago came a new landscape—the one we see today.

The locations and compositions of these igneous rocks tell us a lot about how our earth worked during the flood according to the all-wise and loving Creator’s design to produce the land surfaces we live on. Without these different magma compositions, we wouldn’t have the oceanic and continental crusts which produce our ocean floors and mountains.

The next time you’re at the beach or in the mountains, remember that even the rocks serve their Creator and declare his wisdom and beauty. Just as he designed them to create the landscape of our earth, so he shapes our lives according to his wise, benevolent, and purposeful care.

Dr. Andrew A. Snelling holds a PhD in geology from the University of Sydney and has worked as a consultant research geologist in both Australia and America. Author of numerous scientific articles, Dr. Snelling is now director of research at Answers in Genesis–US.

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