Planetary Surfaces: Why study them? Can they help us find life elsewhere?

Universe Today recently explored the importance of studying impact craters and what they can teach us about finding life beyond Earth. Impact craters are considered one of the many surface processes—others include volcanism, weathering, erosion, and plate tectonics—that shape surfaces on numerous planetary bodies, with all of them simultaneously occurring on Earth. Here, we will explore how and why planetary scientists study planetary surfaces, the challenges faced when studying other planetary surfaces, what planetary surfaces can teach us about finding life, and how upcoming students can pursue studying planetary surfaces, as well. So, why is it so important to study planetary surfaces throughout the solar system?

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Earth Surface

Blue marble Earth. Image credit: NASA

[/caption]Most of the Earth surface, about 70%, is covered with water. The remaining 30% is made up of the seven continental landmasses. Underneath the water that fills the oceans, and the dirt and plants that cover the continents, the Earth’s surface layer is made of rock. This outer layer formed a hard, rocky crust as lava cooled about 4.5 billion years ago. This crust is broken into many large plates(tectonic plates) that move slowly relative to each other. The mountain ranges around the world formed when two plates collided and their edges are forced up. Many other surface features are the result of the movement of these tectonic plates. The plates move anywhere from 25 to 100 mm per year. About 250 million years ago most of the land was connected together.

The rocky layer under the soil of the Earth is called the crust. This comprises the continents and ocean basins. The crust has a variable thickness, being 35-70 km thick on the continents and 5-10 km thick in the ocean basins. The crust is composed mainly of alumino-silicates. The entire crust occupies just 1% of the Earth’s volume. The temperature of the crust increases as you go deeper into the Earth. It starts out cool, but can get up to 400 degrees C at the boundary between the crust and the mantle.

The tectonic plates are actually floating on the molten asthenosphere which is the lower mantle of the Earth. Earthquakes, volcanoes, mountains, and oceanic trench formation occur along plate boundaries. The plates are in constant motion. The reason that tectonic plates are able to move is the Earth’s lithosphere has a higher strength and lower density than the underlying asthenosphere. Their movement is dictated by heat dissipation from the Earth’s mantle. Lateral density variations in the mantle result in convection, which is transferred into plate motion through some combination of frictional drag, downward suction at the subduction zones, and variations in topography and density of the crust that result in differences in gravitational forces.

The Earth’s surface may seemed fixed and permanent to us, but underneath our feet there is constant motion and changes that we may not notice until there is an earthquake or a volcanic eruption. Here on Universe Today we have a great article with interesting facts about Earth. Astronomy Cast offers a good episode about plate tectonics. Here is the NASA webpage about Earth

NASA Earth Observatory
NASA: Continents in Collision
NASA: Structure of the Earth