Model Differentiation Age

λ= decay constant of 182Hf = 0.078 ± 0.002 Myr-1

A Ladder to the Universe: Time and Distance in Space

Figure 1. Ladder of calculating distances in astronomy. The three major rungs are parallax, standard candle, and redshift. Only parallax and redshift will be discussed in this blog post.

The key to understanding how astronomers calculate the distances to the most distant objects begins by taking the first step on the cosmic distance ladder. The first rung of this ladder is called parallax. To visualize this technique, extend your hand and raise your thumb. Now close one eye and take note on the background surrounding your thumb. Open the eye that was previously closed and close the eye that was open, but keep your hand extended. What has happened to your thumb? Does it appear to be moving between closing and opening one eye? Your thumb isn’t moving but the position you are viewing your thumb is changing. This phenomenon is parallax. We take advantage of this property in order to calculate the distances to stars. For Earth’s case, scientists point their telescope at a star, record its location and six months later record the same star’s position. From these measurements, scientist can calculate the angle that the observed star has moved and use that angle and the known distance between the Sun and Earth to calculate the distance to the star.  The diagram below shows how parallax works for Earth. Parallax is limited by the angle that can be measured by scientists. The smaller the angle becomes, the less reliable the measurements become.

Figure 2. Trigonometry of Parallax

The final step to take when finding the distance of the furthest objects in our universe is to find the redshift of the object. Redshift occurs when an object is moving away or towards us. You have experienced this every time you hear an ambulance. Have you ever wondered why when an ambulance is speeding towards you it sounds very loud but once it moves past you the volume decreases? The siren isn’t lowering its value! In fact, this is an example of redshift but with sound. When a star, for example moves away from you, the light it originally released gets stretched, so that it looks redder than it originally is. The opposite occurs when a star is moving towards you; the star appears bluer! This effect becomes more noticeable with objects that are really far away. The value that is given to redshift is related to the amount of time it takes light to travel to your eyes or telescope. By knowing how long it takes the light to reach our eye we can calculate the distance to that object because we know how fast light travels.

Figure 3. Redshift of an object

But why are these distance measurements so important? These values help us understand time in space. When we are looking at the night sky, we are looking at the past. Light travels at incredible speeds but our universe is so large that light becomes delayed. Let’s take our sun for example. If the sun were to explode right now, it would take 8 minutes for us to notice because light takes 8 minutes to travel from the Sun to the Earth. Thus, the objects that are the furthest away from us are the ones that help us peek into the early beginnings of our universe. Once we know the distances to objects, we are able to create a timeline of when things occurred in our universe. Without our ladder to the universe our grasp of our universe would be unbelievably limited.

Ocean Acidification: Can Nemo and Friends Survive?

Figure 1: A fishbowl with clownfish.

Imagine that you have a pet fish (Figure 1). Let’s say it is a clownfish–like from the animated Disney film, Finding Nemo. The bottom of the fish bowl is decorated with an assortment of seashells. You even have some seagrass growing. One day, instead of pouring fish food into the tank, you accidentally grab and pour your can of soda. A situation similar to this is happening in the world’s oceans—only it is carbon dioxide, not soda that is mixing with the water. The result of this process is called ocean acidification.


The burning of fossil fuels as a source of energy has caused a lot of carbon dioxide to be released into the atmosphere. The amount is so high that some carbon dioxide gets absorbed by the ocean. When the carbon dioxide enters the ocean, it starts to form a series of reactions that lead to an increase in hydrogen ions. This causes the water to become more acidic. Hydrogen ions tend to react with carbonate ions. Carbonate ions are the material that make up the shells of organisms, like oysters and clams. One can think of carbonate ions as bricks that are used to build the house in which the animal lives. When hydrogen ions react with carbonate ions, the animal has less bricks that it can use to build its home. In other words, the animal can not grow its shell. Sometimes the hydrogen ions take bricks off of an animal's home—meaning that they cause the shells to dissolve. Sea butterflies, such as the one pictured below (Figure 2), have been negatively impacted by ocean acidification. They are underwater snails that use their feet as wings to move from one place to another. The top image shows a sea butterfly with a healthy shell that is smooth and transparent. The bottom image shows one with an unhealthy shell that has been partially dissolved—the ridges along the shell have become more pronounced, and the shell has some cracks and spots. Like the shells of sea butterflies, the seashells that decorate the fish bowl will also dissolve.

Figure 2: Sea butterflies: the top image shows a transparent, healthy shell. The bottom image shows a partially dissolved shell with cracks and spots.

Now that we have an idea of how the seashells will be affected by the incoming soda, how will the clownfish and seagrass in the fish bowl be affected? The increased acidity of the ocean can in turn cause the blood of fish to increase in acidity. By comparison, if the blood of humans were to become slightly more acidic, we could suffer from seizures or even death. To prevent this, the fish have to use extra energy to make their bodies less acidic. The senses of clownfish could also be affected. The increased acidity of the water makes it difficult for the fish to use chemical signals to distinguish between different habitats. It also becomes difficult for them to detect if another fish is a clownfish or a predator. On the other hand, the sea grasses will actually do well because, like land plants, they require carbon dioxide to breath. However, the harmful effects to marine life outweigh the beneficial effects.

Hotshot Hotspots: Are Mantle Plumes Myth?

We think of Hawaii as a great pimple in the sea, its volcanoes the result of deep inflammation in the form of a hotspot. While we can see that hotspots are sights of active volcanism and thus are fed by hotter magma than their surroundings, we don't exactly know the reason they form. They are distant from the edges of tectonic plates, where the crust will melt and deform based on how the plates interact with one another. When scientists try to image what's going on beneath a hotspot volcano using seismic waves, they see all sorts of different heat distribution patterns.

Figure 1: The results of seismic wave imaging underneath five hotspots from around the world. Red regions are hotter compared to average mantle temperature, and blue is colder. (Nolet, G., Allen, R.M., & Zhao, D., 2007).

The commonly accepted theory is that a mantle plume brings very hot magma to the crust from deep in the mantle. This would help explain why rocks from hotspot volcanoes are distinct from volcanoes at the edges of tectonic plates -- because the magma is coming from different places. Additionally, if these plumes are fixed and a plate moves linearly over them, it would generate the line of volcanoes that's characteristic of a hotspot.

But just because a mantle plume can explain these things doesn't mean they're a scientifically sound theory. The biggest question scientists have, and the one you may be asking is, what is a mantle plume?

Mantle plumes are supposedly shaped like mushrooms, with a distinct bulbous head and thin tail. However, some structures considered mantle plumes may be headless or tailless. The concentrations of chemicals in them differ broadly, including the ones that tell us how deep in the mantle they originated. Scientists have an easier time making new categories to distinguish different mantle plumes than lumping them together.

Figure 2: Idealized image of a mantle plume, showing head and tail (Photo courtesy of Wikimedia Commons).

With so many different variations, it's easy to make the theory work to fit the data instead of the other way around. This ambiguity has pitted scientists against each other, with proponents on both side of the great mantle plume debate. One thing is clear though: we still have a lot to learn about deep Earth processes before we understand what's happening on the surface.

Lunar Lava Tubes: Shelter from an Unlikely Source

                An underground river of molten rock may not sound like it could ever be somewhere hospitable. However, it is possible that the remnants of a lava river like this could help provide shelter for human habitations on the Moon in the future. I am researching lava tubes underneath the surface of the Moon, with the goal of being able to locate them from the surface. Lava tubes are long underground caves that are formed from lava flows, when the surface of the flow cools and crusts over. If this solid crust becomes thick enough, it can become a roof over the lava flow that can support its own weight. When the source of the lava flow stops, the molten rock inside the tube flows out and leaves a hollow underground cave, like a straw. 

Image 1: Lava flow in Hawaii through a lava channel. When a flow like this roofs over, it can form a lava tube. (Image source: Volcanic Features of Hawaii and Other Worlds, USRA (https://www.lpi.usra.edu/publications/slidesets/hawaii/slidepages/slide_09.html))

                Lava tubes are well documented on Earth, and some have become popular destinations for tourists or spelunkers. Nahuku, a tunnel in Hawaii which visitors can walk through, is one example. These tubes can be several meters wide and stretch for kilometers. On the Moon, lava tubes can potentially be much larger, up to kilometers in width; due to the lower gravity on the Moon, larger tubes can exist without collapsing in on themselves. We have not explored inside a lava tube on the Moon, but have found evidence that they exist. We have observed lunar tube skylights, or places where a part of the tube ceiling has fallen in, exposing the tunnel underneath.

Image 2: The interior of Nahuku, a lava tube open to visitors in Hawaii, with people for scale. (Image source: An Enlightening New Experience in Thurston Lava Tube, Hawai'i Volcanoes, National Park Service (https://www.nps.gov/havo/learn/news/20180202_nakuku_lighting.htm))

                We are interested in finding lava tubes on the Moon because they could be extremely useful locations for a potential Moon base. The surface of the Moon is bombarded with radiation and tiny meteorites, which could be harmful to astronauts and any buildings on the surface. These are not an issue on Earth because of the thick atmosphere, which protects from meteorites, and the magnetic field, which blocks radiation. The Moon, however, lacks a magnetic field or atmosphere. If a Moon base was built inside a lava tube, the thick ceiling of rock would protect against these hazards like the roof of a house keeps out rain and harsh sunlight, without extra shielding being required.

Image 3: The location of the Marius Hills Pit, a hole on the surface of the moon thought to be a skylight into a lava tube. The pit is on the path of a sinuous rille, a channel on the lunar surface associated with lava flows. (Image Source: Technology Enabling Exploration of Skylights, Lava Tubes, and Caves, NASA Innovative Advanced Concepts Phase I, NASA (https://www.nasa.gov/pdf/718393main_Whittaker_2011_PhI_Cave_Exploration.pdf))

Image 4: Images of the Marius Hills Pit, taken by the Lunar Reconnaissance Orbiter. (Image Source: Confirmation of Sublunarean Voids and Thin Layering in Mare Deposits, Planetary and Space Science (https://www.sciencedirect.com/science/article/pii/S0032063312001195?via%3Dihub))

I am modeling lava tubes to find how the lunar surface above them would be deformed by their presence, in order to help locate them on the Moon. I am currently using a simplified model of a lava tube’s shape, but I intend to later use a 3D scan of the inside of a real one on Earth instead, for more realistic results.

Ocean Acidification: Can Nemo Survive?

Figure 1: A hypothetical fish bowl with clownfish.

Imagine that you have a pet fish (Figure 1). Let’s say it is a clownfish–like from the animated Disney movie, Finding Nemo. The bottom of the fish bowl is decorated with an assortment of seashells. You even have some seagrass growing. One day, instead of pouring fish food into the tank, you accidentally grab and pour your can of soda. This could have a devastating impact on your mini aquarium. A situation similar to this is happening in the world’s oceans—only it is carbon dioxide, not soda that is mixing with the water. The result of this process is called ocean acidification.

Due to the burning of fossil fuels for energy, there is an elevated amount of carbon dioxide in the atmosphere. Over 25% of this carbon dioxide gets absorbed by the ocean. Once the carbon dioxide molecules enter the ocean, they react with water molecules and carbonate ions (Figure 2). This increases the amount of hydrogen ions in the ocean, causing the ocean to decrease in pH. The decrease in pH has resulted in oceans becoming 30% more acidic. Adding soda to a fish bowl would also decrease the pH of the water because soda is very acidic. 

Figure 2: The process of ocean acidification and its affect on shelled organisms.

Each element of the fish bowl will be affected differently by the incoming soda. The senses of the clownfish could be harmed. The change in the water’s pH makes it difficult for the fish to use chemical signals to distinguish between different habitats. It also becomes difficult for them to detect if another fish is a clownfish or a predator. The shells that decorate the bottom of the fish bowl could dissolve overtime due to the more acidic conditions (Figure 2). Shells are composed of carbonate ions, which react with water and carbon dioxide. In the ocean, live shelled organisms—like oysters and clams—will have difficulty growing their shells because they need carbonate ions to do so. On the other hand, the sea grasses will actually do well because, like land plants, they require carbon dioxide to breath. However, the harmful effects to marine life outweigh the beneficial effects.

A ladder to the Universe: Time and Distance in Space

Usually when we think about finding the distance to an object, we pull out a ruler or tape measure and get to work. But how do we find distances to things we can't see and aren't even on Earth? How can we really know how far away a star is for example? The key to understanding how astronomers calculate the distances to the most distant objects begins by taking the first step on the cosmic distance ladder. The first rung of this ladder is called parallax. To visualize this technique, extend your hand and raise your thumb. Now close one eye and take note on the background surrounding your thumb. Open the eye that was previously closed and close the eye that was open, but keep your hand extended. What has happened to your thumb? Does it appear to be moving between closing and opening one eye? Your thumb isn’t moving but the position you are viewing your thumb is changing. This phenomenon is parallax. We take advantage of this property in order to calculate the distances to stars. For Earth’s case, scientists point their telescope at a star, record its location and six months later record the same star’s position.  The reason they wait six months is because at six months, Earth will be on the opposite side of the Sun. From these measurements, scientist can calculate the angle that the observed star has moved and use that angle and the known distance between the Sun and Earth to calculate the distance to the star.  The diagram below shows how parallax works for Earth. Parallax is limited by the angle that can be measured by scientists. The smaller the angle becomes, the less reliable the measurements become. Additionally, a smaller angle means that the star appears to be ‘moving’ less between measurements, which is the foundation of this method. 

Figure 1 Trigonometry of Parallax

Once the stars stop ‘moving’, it is time to take the next step on the ladder. This is when we start using Standard Candles. Imagine that we have a candle and its directly in front of us. This candle appears to be so bright that you may feel the need to protect your eyes. Now this candle begins to move further and further away from you. As its moving away from you, it looks like the candle is getting dimmer and dimmer. But this is not the case. The candle is still burning at the same brightness it was even when it was close to you. What is changing is how much space the candle is lighting. This means that light is being spread over a larger area and appears to be dimmer than it is. Scientists have created a mathematical relationship to describe the brightness of an object depending on how far away it is from the viewer. Scientists also know objects in the sky that will always have the same brightness. For example, scientists know that when a certain type of star explodes it always explodes with the same level of brightness. When scientists are looking in their telescopes and find these types of stars, they automatically know how bright it should be and compare it how it appears in their telescope. Which this comparison they can calculate the distance to that star. This practice beings to fall apart once you find the last object that you know the brightness of. This then becomes the final distance you can calculate using this technique.

Figure 2 schematic of how redshift works. Depending on the movement of the object, the object will appear redder or bluer to the observer. 

The final step to take when finding the distance of the furthest objects in our universe is to find the redshift of the object. Redshift occurs when an object is moving away or towards us. In fact, you have experienced this every time you hear an ambulance. Have you ever wondered why when an ambulance is speeding towards you it sounds very loud but once it moves past you the volume decreases? The siren isn’t lowering its volume but the sound waves are just being stretched and compressed causing a change in volume. This also happens with light. When a star, for example moves away from you, the light it originally released gets stretched, so that it looks redder than it originally was. The opposite occurs when a star is moving towards you; the star appears bluer! This effect becomes more noticeable with objects that are really far away. The value that is given to redshift is related to the amount of time it takes light to travel to your eyes or telescope. By knowing how long it takes the light to reach our eye we can calculate the distance to that object because we know how fast light travels.

Figure 3.  Hubble images of quasars. In some of the images, you can see the jets of the quasar from the  gas being sucked into the black hole.

But what do all of these distance measurements have to do with time? When we are looking at the night sky, you are actually looking at the past. Light travels at incredible speeds but our universe is so large that light becomes delayed. Let’s take our sun for example. If the sun were to explode right now, it would take 8 minutes for us to notice because light takes 8 minutes to travel from the Sun to the Earth. Thus, the objects that are the furthest away from us are the ones that help us peek into the early beginnings of our universe.  The furthest objects observed by astronomers have been called Quasars. Quasars are the brightest objects in our universe and are made up of a black hole and gas. These objects are hypothesized to be created when two galaxies collide with one another and the black holes at the center of each galaxy becomes one and starts eating all the gas from the galaxies. Imagine you’re looking a tub full of water.  Everything is still until you pull the plug from the drain and the water begins to spiral into the drain. The motion of pulling the plug is identical to two galaxies colliding one another. Quasars have become an important aspect of understanding the history of our universe. Without our ladder to the universe our grasp of our universe would be unbelievably limited.