Mysterious Ocean

The origins of the Earth and moon and the evidence for the first ocean are discussed. We explore answers to the following questions: Were there any continents 4 billion years ago? What would the view from a beach look like 4 billion years ago? How large were the first tides? Was the first ocean salty? What color was the first sky? When did life first arise in the ocean? During its early history, the Earth became a snowball; was the entire ocean ever frozen solid? What is the “albedo effect”?

Oceans have been created, and oceans have been destroyed many times in the Earth’s history by plate tectonics. In this chapter we shall meet Alfred Wegner and learn about his early theory of continental drift and its problems. Rivals to Wegner’s theory were the shrinking Earth theory and the expanding Earth theory, but they had problems of their own. We will meet Marie Tharp and her discovery of the great rift valley that encircles the globe. The “Rosetta Stone” for plate tectonic theory was the discovery of magnetic “stripes” on the ocean floor created by episodic reversals of the Earth’s magnetic field. The disintegration of Pangea 170 million years ago and the rise and fall of the Tethys Ocean 6 million years ago are merely brief stages of the cycle of the birth and death of oceans.

Did you ever wonder where the continents came from? Their creation is related to plate tectonic subduction zones and the melting of ocean crust. The subduction zones are like a giant “refinery” which results in the gradual accretion of continents. In this chapter we will learn how to think in “deep time”: thousands, millions, and billions of years. The first sexual reproduction occurred in the ocean less than a billion years ago, but for over 3 billion years before that, the oceans contained strange-shaped mounds made of sediment called “stromatolites” created by cyanobacteria. The Cambrian Period saw the explosion of life, but the fossil record we have is very patchy because the chances for any plant or animal to become a fossil are less than one in a million. The formation of the modern ocean basins began only around 180 million years ago – isn’t it strange that the ocean floor and ocean basins are so much younger than the ocean water they contain?

How deep is the ocean? To find the answer to this question is not as simple as you may think. Ocean mapping technology has developed over time, and there have been many advances like the invention of sonar. But it is a fact that Mars is better mapped than of our own ocean floor. The search for the missing Malaysian Airline Flight MH370 in the Indian Ocean illustrates how poorly our oceans are mapped. In this chapter we will learn how to take a piston core sample of the ocean floor, and we will meet Maurice (Doc) Ewing and learn how he invented seismic profiling so that we could “see” the layers of rocks and sediment beneath the ocean floor. But all of our sonars and seismic systems make a lot of noise. How has this impacted on marine mammals and other ocean creatures?

The ocean is restless. It never stops moving. The famous American oceanographer Matthew Maury described the Gulf Stream ocean current as “a river in the sea,” but all the world’s rivers combined transport only a tiny fraction of the volume of ocean currents. The great ocean currents regulate the climate by transporting heat around the globe, taking warm water from the equator toward the poles and cool water from the poles toward the equator. Water evaporates from the ocean, falls as rain on the land, and returns to the sea. In this chapter we will learn about the Coriolis effect, one of the most important concepts in oceanography and its consequences for wind and ocean currents. Eddies shed from the ocean currents can reach to great depths and cause deep ocean “storms.” We will answer important questions like: What would happen if ice did not float? Why don’t icebergs drift in the same direction as the wind blows? What is storm “wave base”? What does a tsunami wave look like in the middle of the ocean? Why are there new beaches forming on the Arctic coast? What has caused Antarctic sea ice “factories” to close down?

The polar seas are the lungs of the ocean. When sea ice forms, it makes cold and salty water that is enriched in oxygen. Polar seas are where the oceans “breathe in.” Oxygen dead zones are created where rivers polluted by fertilizer reach the ocean and are a growing concern globally. Carbon dioxide is also absorbed by the ocean along with oxygen in the polar seas. In seawater carbon dioxide makes weak carbonic acid causing ocean acidification, the “evil twin” of global warming. But the oceans have not always had lungs that work the way they do today. In the geologic past, the deep ocean waters were hot, salty, and sometimes deprived of oxygen. We will also learn about a time 6 million years ago when the Strait of Gibraltar was closed off and the Mediterranean Sea nearly dried up.

The world has two major ice sheets – in Antarctica and Greenland – but their histories are completely different. The Antarctic ice sheet evolved over 30 million years ago when South America separated from Antarctica to create the Drake Passage. This allowed the Circumpolar Current to form, isolating Antarctica and turning it into the coldest, highest, and driest continent. Greenland is the last major remnant of continental ice sheets that have grown over large parts of North America and Europe repeatedly for the last 2 million years. In this chapter, we will meet Milutin Milanković and learn about his theory for ice ages. Ice sheets over Europe and North America lowered sea level by 130 m, and when they melted, there were huge floods in Washington State in the west, as well as in Eastern Canada. The rising sea level had many consequences: it refilled the Black Sea, possibly explaining the biblical flood story. Rising sea level flooded the Gulf of Carpentaria in Australia and the Persian Gulf Oasis. All the fish, kelp, and corals living on the continental shelves today, including the Great Barrier Reef, are recent arrivals that only moved in over the last 10,000 years or so.

In the next two chapters, we will take a tour aboard an imaginary hover car to visit the world’s continental shelves and the deep ocean. The continental shelf (as the name suggests) is the submerged part of the continents, and the features we see underwater are comparable to those we see today along the coast. The continental shelf is where rivers disgorge their loads of sediment and where glaciers built moraines during the ice age, providing the material needed to make sandbanks. Sand is in fact the second most used commodity on Earth after freshwater. It is a key ingredient of concrete and is also used to replenish beaches that are eroding because of rising sea level. In this chapter we will observe the impacts of bottom trawl fishing on seabed habitats and consider the need for marine parks. We will explore hidden coral reefs in the Gulf of Carpentaria and see how bleaching of corals is happening more and more often. Has a tipping point been passed? Will we be able to save the coral reefs? To avoid burning fossil fuels, we should look at harnessing the ocean’s tide power as a renewable power source. Human impacts on land often reach the ocean. The Ok Tedi gold mine disaster in the Fly River, Papua New Guinea, is an example of this.

Still on board our hover car, in this chapter we will explore the deep ocean’s submarine canyons, seamounts, plateaus, deep ocean trenches, and the mid-ocean ridge. We will meet pioneer marine geologist Francis Shepard and learn how submarine canyons are formed by underwater landslides. We will learn that there is a connection between the testing of nuclear bombs in the Pacific and Charles Darwin’s theory for the formation of coral atolls. We will learn about Zealandia, the 8th undiscovered continent. We will ponder what creatures inhabit deep-sea sediments leaving only traces in the mud of their existence and what happens to its body when a whale dies. Will humans mine manganese nodule deposits on the deep ocean floor, knowing that once destroyed this habitat will never recover? To mine or not to mine – it is a moral dilemma.

This last chapter will review the strange and fickle (geologic) times we live in and the future of our oceans. In the next century, climate change will cause the demise of coral reefs, warmer and more acidic oceans, the poleward migration of species, melting of ice sheets, and thus at least 3 m (10 feet) of sea level rise. There is no such thing as “sustainable growth” in a finite ocean, and so we simply must choose which future we want to have for our civilization and our ocean. Further into the future, we can predict a new ice age beginning after around 10,000 years. Even further into the future, plate tectonics predicts a supercontinent “Pangea Proxima” will be formed in a few hundreds of million years. The oceans will evaporate when the sun becomes a “red giant” in around 1 billion years. The oceans remain largely unexplored, and many mysteries remain for future generations to solve.