Introduction to Earth Science: The Earth

The Earth is a dynamic planet. The inner heat it holds inside drives some of the processes we see at the surface, such as volcanoes, earthquakes, mountain building, and plate tectonics. The other rocky planets in our solar system — the Moon, Mercury, Venus, and Mars — are smaller and have lost most or all of their internal heat. Although some have mountains and volcanoes, they do not form as a result of plate tectonic processes as they do on Earth.

The heat that comes from the Sun drives other processes, like the weather, climate, ocean currents, and erosion. It turns out that we are a perfect distance from the Sun. We are just the right distance for a dynamic atmosphere; for the conditions necessary for water to exist as a gas, liquid and solid; and, of course, the right distance for life. There may be other life in our solar system; scientists are looking at Mars and Jupiter’s moon, Europa, for evidence of current or past life. But even if we have company in our solar system, it would be more simple than life on Earth.

Geology is the study of our planet. Many geologists are interested in what’s happening on Earth right now. These scientists include volcanologists, who go to erupting volcanoes to understand the processes that led to the eruption so that they can better predict future eruptions. They include seismologists, who set up sophisticated equipment near earthquake faults and dig trenches in fault zones to understand what causes earthquakes. Geologists monitor floods, study the changes in landforms, and observe how the composition of the atmosphere and ocean affect one another.

Other geologists study the history of the Earth. Historical geologists tell tales of long-past events: that single-celled organisms were the only life forms for 3 of the Earth’s 4.6 billion years; that the dinosaurs ruled the world for 160 million years until a giant asteroid wiped them out 65 million years ago; that ice covered much of our planet in the time between 1.8 million and 10,000 years ago. But how do they know these things? What evidence is there of events that happened millions of years ago?

The evidence is in rocks, which may seem lifeless, but are really incredible storytellers. When studying rocks, geologists are guided by the motto, “the present is the key to the past.” If the lava that shoots out of Kilauea volcano in Hawaii cools into a smooth black rock called basalt, finding old basalt formations in a rock pile tells us that a Kilauea–like volcano once erupted nearby, even if the volcano has long since disappeared. The basis of this thinking is that although there may be different environmental conditions in different places or times, we can assume that the physical and chemical laws of nature are the same for all time periods and all planetary bodies. This is called uniformitarianism.

What we know about the Earth comes from:

• analyzing the chemistry of rocks and minerals,

• conducting experiments to determine the temperatures and pressures at which certain minerals and

rocks are stable,

• determining the ages of those rocks and minerals,

• studying the history of life through fossils,

• constructing geological maps of areas to understand the processes that lead to different landforms,

• using satellites, seismic equipment, and other techniques to understand plate tectonic movements,

• studying other planets and their satellites,

• observations.