Hundreds of millions of years ago, Earth went through two episodes of severe glaciation. These two episodes—the Sturtian and the Marinoan glaciations—occured during the Earth’s Cryogenian Period. The Cryogenian lasted from about 720 million to 635 million years ago.
The phenomenon is called “Snowball Earth” and both instances of it happened in pretty quick succession. And while a planet encased in ice and snow sounds devastating, these episodes may have paved the way for the development of complex life.
The question is, what caused the Earth to freeze over like that?
The Moon is easily the most well-studied object in the Solar System, (other than Earth, of course.) But it still holds some puzzles for scientists. Why, for instance, is one side of the Moon so different from the other?
In 1978, NASA’s Pioneer Venus (aka. Pioneer 12) mission reached Venus (“Earth’s Sister”) and found indications that Venus may have once had oceans on its surface. Since then, several missions have been sent to Venus and gathered data on its surface and atmosphere. From this, a picture has emerged of how Venus made the transition from being an “Earth-like” planet to the hot and hellish place it is today.
It all started about 700 million years ago when a massive resurfacing event triggered a runaway Greenhouse Effect that caused Venus’s atmosphere to become incredibly dense and hot. This means that for 2 to 3 billion years after Venus formed, the planet could have maintained a habitable environment. According to a recent study, that would have been long enough for life to have emerged on “Earth’s Sister”.
When looking for potentially-habitable extra-solar planets, scientists are somewhat restricted by the fact that we know of only one planet where life exists (i.e. Earth). For this reason, scientists look for planets that are terrestrial (i.e. rocky), orbit within their star’s habitable zones, and show signs of biosignatures such as atmospheric carbon dioxide – which is essential to life as we know it.
This gas, which is the largely result of volcanic activity here on Earth, increases surface heat through the greenhouse effect and cycles between the subsurface and the atmosphere through natural processes. For this reason, scientists have long believed that plate tectonics are essential to habitability. However, according to a new study by a team from Pennsylvania State University, this may not be the case.
On Earth, volcanism is the result of plate tectonics and occurs where two plates collide. This causes subduction, where one plate is pushed beneath the other and deeper into the subsurface. This subduction changes the dense mantle into buoyant magma, which rises through the crust to the Earth’s surface and creates volcanoes. This process can also aid in carbon cycling by pushing carbon into the mantle.
Plate tectonics and volcanism are believe to have been central to the emergence of life here on Earth, as it ensured that our planet had sufficient heat to maintain liquid water on its surface. To test this theory, Professors Foley and Smye created models to determine how habitable an Earth-like planet would be without the presence of plate tectonics.
These models took into account the thermal evolution, crustal production and CO2 cycling to constrain the habitability of rocky, Earth-sized stagnant lid planets. These are planets where the crust consists of a single, giant spherical plate floating on mantle, rather than in separate pieces. Such planets are thought to be far more common than planets that experience plate tectonics, as no planets beyond Earth have been confirmed to have tectonic plates yet. As Prof. Foley explained in a Penn State News press release:
“Volcanism releases gases into the atmosphere, and then through weathering, carbon dioxide is pulled from the atmosphere and sequestered into surface rocks and sediment. Balancing those two processes keeps carbon dioxide at a certain level in the atmosphere, which is really important for whether the climate stays temperate and suitable for life.”
Essentially, their models took into account how much heat a stagnant lid planet’s climate could retain based on the amount of heat and heat-producing elements present when the planet formed (aka. its initial heat budget). On Earth, these elements include uranium which produces thorium and heat when it decays, which then decays to produce potassium and heat.
After running hundreds of simulations, which varied the planet’s size and chemical composition, they found that stagnant lid planets would be able to maintain warm enough temperatures that liquid water could exist on their surfaces for billions of years. In extreme cases, they could sustain life-supporting temperatures for up to 4 billion years, which is almost the age of the Earth.
As Smye indicated, this is due in part to the fact that plate tectonics are not always necessary for volcanic activity:
“You still have volcanism on stagnant lid planets, but it’s much shorter lived than on planets with plate tectonics because there isn’t as much cycling. Volcanoes result in a succession of lava flows, which are buried like layers of a cake over time. Rocks and sediment heat up more the deeper they are buried.”
The researchers also found that without plate tectonics, stagnant lid planets could still have enough heat and pressure to experience degassing, where carbon dioxide gas can escape from rocks and make its way to the surface. On Earth, Smye said, the same process occurs with water in subduction fault zones. This process increases based on the quantity of heat-producing elements present in the planet. As Foley explained:
“There’s a sweet spot range where a planet is releasing enough carbon dioxide to keep the planet from freezing over, but not so much that the weathering can’t pull carbon dioxide out of the atmosphere and keep the climate temperate.”
According to the researchers’ model, the presence and amount of heat-producing elements were far better indicators for a planet’s potential to sustain life. Based on their simulations, they found that the initial composition or size of a planet is very important for determining whether or not it will become habitable. Or as they put it, the potential habitability of a planet is determined at birth.
By demonstrating that stagnant lid planets could still support life, this study has the potential for greatly extending the range of what scientists consider to be potentially-habitable. When the James Webb Space Telescope (JWST) is deployed in 2021, examining the atmospheres of stagnant lid planets to determine the presence of biosignatures (like CO2) will be a major scientific objective.
Knowing that more of these worlds could sustain life is certainly good news for those who are hoping that we find evidence of extra-terrestrial life in our lifetimes.
Whenever the existence of an extra-solar planet is confirmed, there is reason to celebrate. With every new discovery, humanity increases the odds of finding life somewhere else in the Universe. And even if that life is not advanced enough (or particularly inclined) to build a radio antenna so we might be able to hear from them, even the possibility of life beyond our Solar System is exciting.
Unfortunately, determining whether or not a planet is habitable is difficult and subject to a lot of guesswork. While astronomers use various techniques to put constraints on the size, mass, and composition of extra-solar planets, there is no surefire way to know if these worlds are habitable. But according to a new study from a team of astronomers from Cornell University, looking for signs of volcanic activity could help.
Their study – titled “A Volcanic Hydrogen Habitable Zone” – was recently published in The Astrophysical Journal Letters. According to their findings, the key to zeroing in on life on other planets is to look for the telltale signs of volcanic eruptions – namely, hydrogen gas (H²). The reason being is that this, and the traditional greenhouse gases, could extend the habitable zones of stars considerably.
“On frozen planets, any potential life would be buried under layers of ice, which would make it really hard to spot with telescopes. But if the surface is warm enough – thanks to volcanic hydrogen and atmospheric warming – you could have life on the surface, generating a slew of detectable signatures.”
Planetary scientists theorize that billions of years ago, Earth’s early atmosphere had an abundant supply of hydrogen gas (H²) due to volcanic outgassing. Interaction between hydrogen and nitrogen molecules in this atmosphere are believed to have kept the Earth warm long enough for life to develop. However, over the next few million years, this hydrogen gas escaped into space.
This is believed to be the fate of all terrestrial planets, which can only hold onto their planet-warming hydrogen for so long. But according to the new study, volcanic activity could change this. As long as they are active, and their activity is intense enough, even planets that are far from their stars could experience a greenhouse effect that would be sufficient to keep their surfaces warm.
Consider the Solar System. When accounting for the traditional greenhouse effect caused by nitrogen gas (N²), carbon dioxide and water, the outer edge of our Sun’s habitable zone extends to a distance of about 1.7 AU – just outside the orbit of Mars. Beyond this, the condensation and scattering of CO² molecules make a greenhouse effect negligible.
However, if one factors in the outgassing of sufficient levels of H², that habitable zone can extend that outer edge to about 2.4 AUs. At this distance, planets that are the same distance from the Sun as the Asteroid Belt would theoretically be able to sustain life – provided enough volcanic activity was present. This is certainly exciting news, especially in light of the recent announcement of seven exoplanets orbiting the nearby TRAPPIST-1 star.
Of these planets, three are believed to orbit within the star’s habitable zone. But as Lisa Kaltenegger – also a member of the Carl Sagan Institute and the co-author on the paper – indicated, their research could add another planet to this
“Finding multiple planets in the habitable zone of their host star is a great discovery because it means that there can be even more potentially habitable planets per star than we thought. Finding more rocky planets in the habitable zone – per star – increases our odds of finding life… Although uncertainties with the orbit of the outermost Trappist-1 planet ‘h’ means that we’ll have to wait and see on that one.”
Another upside of this study is that the presence of volcanically-produced hydrogen gas would be easy to detect by both ground-based and space-based telescopes (which routinely conduct spectroscopic surveys on distant exoplanets). So not only would volcanic activity increase the likelihood of there being life on a planet, it would also be relatively easy to confirm.
“We just increased the width of the habitable zone by about half, adding a lot more planets to our ‘search here’ target list,” said Ramirez. “Adding hydrogen to the air of an exoplanet is a good thing if you’re an astronomer trying to observe potential life from a telescope or a space mission. It increases your signal, making it easier to spot the makeup of the atmosphere as compared to planets without hydrogen.”
It is, of course, far too soon to say if this study will help in our search for extra-solar life. But in the coming years, we may find ourselves one step closer to resolving that troublesome Fermi Paradox!
Volcanoes are an impressive force of nature. Physically, they dominate the landscape, and have an active role in shaping our planet’s geography. When they are actively erupting, they are an extremely dangerous and destructive force. But when they are passive, the soil they enrich can become very fertile, leading to settlements and cities being built nearby.
Such is the nature of volcanoes, and is the reason why we distinguish between those that are “active” and those that are “dormant”. But what exactly is the differences between the two, and how do geologists tell? This is actually a complicated question, because there’s no way to know for sure if a volcano is all done erupting, or if it’s going to become active again.
Put simply, the most popular way for classifying volcanoes comes down to the frequency of their eruption. Those that erupt regularly are called active, while those that have erupted in historical times but are now quiet are called dormant (or inactive). But in the end, knowing the difference all comes down to timing!
Currently, there is no consensus among volcanologists about what constitutes “active”. Volcanoes – like all geological features – can have very long lifespans, varying between months to even millions of years. In the past few thousand years, many of Earth’s volcanoes have erupted many times over, but currently show no signs of impending eruption.
As such, the term “active” can mean only active in terms of human lifespans, which are entirely different from the lifespans of volcanoes. Hence why scientists often consider a volcano to be active only if it is showing signs of unrest (i.e. unusual earthquake activity or significant new gas emissions) that mean it is about to erupt.
By this definition, those volcanoes that have erupted in the course of human history (which includes more than 500 volcanoes) are defined as active. However, this too is problematic, since this varies from region to region – with some areas cataloging volcanoes for thousands of years, while others only have records for the past few centuries.
As such, an “active volcano” can be best described as one that’s currently in a state of regular eruptions. Maybe it’s going off right now, or had an event in the last few decades, or geologists expect it to erupt again very soon. In short, if its spewing fire or likely to again in the near future, then it’s active!
Meanwhile, a dormant volcano is used to refer to those that are capable of erupting, and will probably erupt again in the future, but hasn’t had an eruption for a very long time. Here too, definitions become complicated since it is difficult to distinguish between a volcano that is simply not active at present, and one that will remain inactive.
Volcanoes are often considered to be extinct if there are no written records of its activity. Nevertheless, volcanoes may remain dormant for a long period of time. For instance, the volcanoes of Yellowstone, Toba, and Vesuvius were all thought to be extinct before their historic and devastating eruptions.
The same is true of the Fourpeaked Mountain eruption in Alaska in 2006. Prior to this, the volcano was thought to be extinct since it had not erupted for over 10,000 years. Compare that to Mount Grímsvötn in south-east Iceland, which erupted three times in the past 12 years (in 2011, 2008 and 2004, respectively).
And so a dormant volcano is actually part of the active volcano classification, it’s just that it’s not currently erupting.
Geologists also employ the category of extinct volcano to refer to volcanoes that have become cut off from their magma supply. There are many examples of extinct volcanoes around the world, many of which are found in the Hawaiian-Emperor Seamount Chain in the Pacific Ocean, or stand individually in some areas.
For example, the Shiprock volcano, which stands in Navajo Nation territory in New Mexico, is an example of a solitary extinct volcano. Edinburgh Castle, located just outside the capitol of Edinburgh, Scotland, is famously located atop an extinct volcano.
But of course, determining if a volcano is truly extinct is often difficult, since some volcanoes can have eruptive lifespans that measure into the millions of years. As such, some volcanologists refer to extinct volcanoes as inactive, and some volcanoes once thought to be extinct are now referred to as dormant.
In short, knowing if a volcano is active, dormant, or extinct is complicated and all comes down to timing. And when it comes to geological features, timing is quite difficult for us mere mortals. Individuals and generations have limited life spans, nations rise and fall, and even entire civilization sometimes bite the dust.
But volcanic formations? They can endure for millions of years! Knowing if there still life in them requires hard work, good record-keeping, and (above all) immense patience.
Volcanoes come in many shapes and sizes, ranging from common cinder cone volcanoes that build up from repeated eruptions and lava domes that pile up over volcanic vents to broad shield volcanoes and composite volcanoes. Though they differ in terms of structure and appearance, they all share two things. On the one hand, they are all awesome forces of nature that both terrify and inspire.
On the other, all volcanic activity comes down to the same basic principle. In essence, all eruptions are the result of magma from beneath the Earth being pushed up to the surface where it erupts as lava, ash and rock. But what mechanisms drive this process? What is it exactly that makes molten rock rise from the Earth’s interior and explode onto the landscape?
To understand how volcanoes erupt, one first needs to consider the structure of the Earth. At the very top is the lithosphere, the outermost layers of the Earth that consists of the upper mantle and crust. The crust makes up a tiny volume of the Earth, ranging from 10 km in thickness on the ocean floor to a maximum of 100 km in mountainous regions. It is cold and rigid, and composed primarily of silicate rock.
Beneath the crust, the Earth’s mantle is divided into sections of varying thickness based on their seismology. These consist of the upper mantle, which extends from a depth of 7 – 35 km (4.3 to 21.7 mi)) to 410 km (250 mi); the transition zone, which ranges from 410–660 km (250–410 mi); the lower mantle, which ranges from 660–2,891 km (410–1,796 mi); and the core–mantle boundary, which is ~200 km (120 mi) thick on average.
In the mantle region, conditions change drastically from the crust. Pressures increase considerably and temperatures can reach up to 1000 °C, which makes the rock viscous enough that it behaves like a liquid. In short, it experiences elastically on time scales of thousands of years or greater. This viscous, molten rock collects into vast chambers beneath the Earth’s crust.
Since this magma is less dense than the surrounding rock, it ” floats” up to the surface, seeking out cracks and weaknesses in the mantle. When it finally reaches the surface, it explodes from the summit of a volcano. When it’s beneath the surface, the molten rock is called magma. When it reaches the surface, it erupts as lava, ash and volcanic rocks.
With each eruption, rocks, lava and ash build up around the volcanic vent. The nature of the eruption depends on the viscosity of the magma. When the lava flows easily, it can travel far and create wide shield volcanoes. When the lava is very thick, it creates a more familiar cone volcano shape (aka. a cinder cone volcano). When the lava is extremely thick, it can build up in the volcano and explode (lava domes).
Another mechanism that drives volcanism is the motion the crust undergoes. To break it down, the lithosphere is divided into several plates, which are constantly in motion atop the mantle. Sometimes the plates collide, pull apart, or slide alongside each other; resulting in convergent boundaries, divergent boundaries, and transform boundaries. This activity is what drives geological activity, which includes earthquakes and volcanoes.
In the case of the former, subduction zones are often the result, where the heavier plate slips under the lighter plate – forming a deep trench. This subduction changes the dense mantle into buoyant magma, which rises through the crust to the Earth’s surface. Over millions of years, this rising magma creates a series of active volcanoes known as a volcanic arc.
In short, volcanoes are driven by pressure and heat in the mantle, as well as tectonic activity that leads to volcanic eruptions and geological renewal. The prevalence of volcanic eruptions in certain regions of the world – such as the Pacific Ring of Fire – also has a profound impact on the local climate and geography. For example, such regions are generally mountainous, have rich soil, and periodically experience the formation of new landmasses.
Few forces in nature are are impressive or frightening as a volcanic eruption. In an instant, from within the rumbling depths of the Earth, hot lava, steam, and even chunks of hot rock are spewed into the air, covering vast distances with fire and ash. And thanks to the efforts of geologists and Earth scientists over the course of many centuries, we have to come to understand a great deal about them.
However, when it comes to the nomenclature of volcanoes, a point of confusion often arises. Again and again, one of the most common questions about volcanoes is, what is the difference between lava and magma? They are both molten rock, and are both associated with volcanism. So why the separate names? As it turns out, it all comes down to location.
As anyone with a basic knowledge of geology will tell you, the insides of the Earth are very hot. As a terrestrial planet, its interior is differentiated between a molten, metal core, and a mantle and crust composed primarily of silicate rock. Life as we know it, consisting of all vegetation and land animals, live on the cool crust, whereas sea life inhabits the oceans that cover a large extent of this same crust.
However, the deeper one goes into the planet, both pressures and temperatures increase considerably. All told, Earth’s mantle extends to a depth of about 2,890 km, and is composed of silicate rocks that are rich in iron and magnesium relative to the overlying crust. Although solid, the high temperatures within the mantle cause pockets of molten rock to form.
This silicate material is less dense than the surrounding rock, and is therefore sufficiently ductile that it can flow on very long timescales. Over time, it will also reach the surface as geological forces push it upwards. This happens as a result of tectonic activity.
Basically, the cool, rigid crust is broken into pieces called tectonic plates. These plates are rigid segments that move in relation to one another at one of three types of plate boundaries. These are known as convergent boundaries, at which two plates come together; divergent boundaries, at which two plates are pulled apart; and transform boundaries, in which two plates slide past one another laterally.
Interactions between these plates are what is what is volcanic activity (best exemplified by the “Pacific Ring of Fire“) as well as mountain-building. As the tectonic plates migrate across the planet, the ocean floor is subducted – the leading edge of one plate pushing under another. At the same time, mantle material will push up at divergent boundaries, forcing molten rock to the surface.
As already noted, both lava and magma are what results from rock superheated to the point where it becomes viscous and molten. But again, the location is the key. When this molten rock is still located within the Earth, it is known as magma. The name is derived from Greek, which translate to “thick unguent” (a word used to describe a viscous substance used for ointments or lubrication).
It is composed of molten or semi-molten rock, volatiles, solids (and sometimes crystals) that are found beneath the surface of the Earth. This vicious rock usually collects in a magma chamber beneath a volcano, or solidify underground to form an intrusion. Where it forms beneath a volcano, it can then be injected into cracks in rocks or issue out of volcanoes in eruptions. The temperature of magma ranges between 600 °C and 1600 °C.
Magma is also known to exist on other terrestrial planets in the Solar System (i.e. Mercury, Venus and Mars) as well as certain moons (Earth’s Moon and Jupiter’s moon Io). In addition to stable lava tubes being observed on Mercury, the Moon and Mars, powerful volcanoes have been observed on Io that are capable of sending lava jets 500 km (300 miles) into space.
When magma reaches the surface and erupts from a volcano, it officially becomes lava. There are actually different kinds of lava depending on its thickness or viscosity. Whereas the thinnest lava can flow downhill for many kilometers (thus creating a gentle slope), thicker lavas will pile up around a volcanic vent and hardly flow at all. The thickest lava doesn’t even flow, and just plugs up the throat of a volcano, which in some cases cause violent explosions.
The term lava is usually used instead of lava flow. This describes a moving outpouring of lava, which occurs when a non-explosive effusive eruption takes place. Once a flow has stopped moving, the lava solidifies to form igneous rock. Although lava can be up to 100,000 times more viscous than water, lava can flow over great distances before cooling and solidifying.
The word “lava” comes from Italian, and is probably derived from the Latin word labes which means “a fall” or “slide”. The first use in connection with a volcanic event was apparently in a short written account by Franscesco Serao, who observed the eruption of Mount Vesuvius between May 14th and June 4th, 1737. Serao described “a flow of fiery lava” as an analogy to the flow of water and mud down the flanks of the volcano following heavy rain.
Such is the difference between magma and lava. It seems that in geology, as in real estate, its all about location!
By definition, pollution refers to any matter that is “out of place”. In other words, it is what happens when toxins, contaminants, and other harmful products are introduced into an environment, disrupting its normal patterns and functions. When it comes to our atmosphere, pollution refers to the introduction of chemicals, particulates, and biological matter that can be harmful to humans, plants and animals, and cause damage to the natural environment.
Whereas some causes of pollution are entirely natural – being the result of sudden changes in temperature, seasonal changes, or regular cycles – others are the result of human impact (i.e. anthropogenic, or man-made). More and more, the effects of air pollution on our planet, especially those that result from human activity, are of great concern to developers, planners and environmental organizations, given the long-term effect they can have.
Venus is often referred to as “Earth’s Twin” (or “sister planet”), and for good reason. Despite some rather glaring differences, not the least of which is their vastly different atmospheres, there are enough similarities between Earth and Venus that many scientists consider the two to be closely related. In short, they are believed to have been very similar early in their existence, but then evolved in different directions.
Earth and Venus are both terrestrial planets that are located within the Sun’s Habitable Zone (aka. “Goldilocks Zone”) and have similar sizes and compositions. Beyond that, however, they have little in common. Let’s go over all their characteristics, one by one, so we can in what ways they are different and what ways they are similar.