3 Things you should know about geoid models of Earth’s variable gravity, harmful invasive insect species, and synthetic diamonds

Sep 17, 2024

Shaping the Earth with Gravity

The Earth's shape is not a sphere, but an imperfect ellipsoid ― a slightly squashed sphere with a highly uneven surface. Though useful for generating map projections and measuring distance across the surface, ellipsoid models of the Earth’s shape have an unrealistically smooth surface. With measurements from Earth’s gravitational field, scientists can model Earth’s shape and its uneven surface. This gravity model, called a geoid, is an imaginary undulating sea level surface around the planet created to act as a reference surface for measuring elevations over both land and sea, and for understanding how gravity varies around the planet.

Gravity is of course the force of attraction between two masses. Although every object on our planet has mass, Earth’s mass is not evenly distributed around the globe. For instance, Earth has a significant range in topography from the mass of mountain ranges with an elevation up to 8.8 km above sea level (Mount Everest), to the deepest ocean trench, the Challenger Deep, 10.9 km below sea level.

A spinning Earth using colours to show variations in gravity around the globe.

Photo Credit

NASA/JPL/University of Texas Center for Space Research

A gravity model created from satellite measurements by NASA’s GRACE mission showing variations in Earth’s gravity field. Red areas indicate stronger gravity, and blue areas indicate weaker gravity.

Earth's gravity, which on average is understood to be 9.8 m/s², varies with location, time, latitude, height, and regional mass density. Gravity can change due to several factors, including changes in topography, rock type, surface water, groundwater, and rapidly melting glaciers. Mass on Earth is continually redistributed, due to tides, earthquakes, volcanic eruptions, mining and petroleum extraction, glacial rebound, etc. Sea-level changes add mass to the oceans and remove it from land, with local gravity influencing the surface height of the ocean. For example, when a glacier melts, the average sea level rises, but near the glacier, the loss of ice mass can reduce gravity.

The gravitational field can be measured by a vast array of terrestrial, marine, and airborne gravity survey data, in addition to satellites measurements such as NASA’s GRACE and the European Space Agency’s GOCE missions. Measurements can be made using gravimeters, or calculations of the difference in acceleration and distance between two sites or between two or more satellites.

Among its many uses, the geoid is incredibly important for global positioning (GPS) and mapping, particularly as a reference for vertical measurements relative to mean sea level. Accurate elevation data are required for topographic maps and land surveying; it’s critical for large engineering projects such as building dams, bridges, and tunnels; for sea level monitoring and impacts of climate change on Canada’s coastlines, flood risk assessments, a wide variety of geology related uses from resource mining to earthquake monitoring, land use planning, oceanography and atmospheric sciences, and finally Earth Observation. Geoid data help ensure that various scientific and practical applications rely on consistent and precise geographic information.

Fitting geographical coordinate systems to the Earth’s irregular shape is very challenging. Latitude and longitude, for example, are defined using an ellipsoid model, and elevations based on the geoid.

Different datums (reference systems) use different estimates for the precise shape and size of the earth, but no projection nor map is perfect.

The geoid provides a more accurate representation of Earth's shape than a simple ellipsoid. By accounting for gravitational variations and the Earth's uneven surface, it supports a wide range of scientific and practical applications, ensuring consistency and precision in geographic information.

Go Further

More on the origin of geodesy, the study of Earth’s shape

Details on Canada’s geoid and NRCAN Height Reference System Modernization: Canadian Geodetic Vertical Datum of 2013

Canadian Gravity Standardization Network (CGSN) – control stations all over the country

Canadian Geodetic Survey of Natural Resources Canada

Mission to map the Moon’s gravity: GRAIL (Gravity Recovery and Interior Laboratory)

By Cassandra Marion

Canada vs. The Japanese Beetle: A Tiny Terror on the Loose

There's a little invader causing a lot of frustrations for gardeners and farmers in Canada : the Japanese beetle. You've likely seen them yourself – shiny, metallic green and coppery beetles, often found copulating in masses on our plants. Over the summer months, this ravenous insect wreaks havoc on ornamental plants and crops across Canada, leaving behind skeletonized leaves and bare plants. But luckily, by now (September), our plants can recover a bit because above-ground plant munching has ramped down for the year, as beetles die off and their progeny continue their lifecycles underground. But is there a way to get rid of them for good? Don’t hold your breath…

A zoomed-in view of a cluster of coppery beetles devouring a rose flower, with rose leaves surrounding them.

Photo Credit

InCommunicado | iStock

Rosebush flowers are one of Japanese beetles’ favourite foods.

The Japanese beetle, as its name implies, hails from Japan. It accidentally hitched a ride to New Jersey back in 1916 and, by 1939, it had found its way into Canada. Now, these beetles have spread through Ontario, Quebec, and beyond. They have invaded and settled in most provinces, meaning our chances of eradicating them are extremely slim. There is still one province that has been spared, likely because of the mountain range separating it from the rest of the country – British Columbia. And the Canadian Food Inspection Agency (CFIA) is taking hard measures to try and keep it that way.

Part of why they are so destructive is their seemingly indiscriminate appetite. Unlike many other bugs which prefer specific hosts, Japanese beetles feed on more than 300 types of plants, including soybeans, roses, grapevines, fruit trees, and even corn! They start at the top of a plant or tree, work their way down, and consume not only the leaves but also flower petals and soft fruit like peaches and raspberries, as well as the silks on ears of corn.

Over their 40-day adult lives, female beetles lay 40 to 60 eggs underground, usually in grassy areas. These eggs hatch into hungry little grubs that feast on roots and organic matter. After a few months of chowing down, they take a winter break before growing into full-fledged adults the next spring, emerging from the soil in June to continue their campaign of destruction.

Despite their long history in North America, we’re still searching for the perfect way to deal with these beetles. Pesticides were once the go-to solution, but their negative impact on other wildlife has largely taken them off the table. So, what can you do?

One of the most effective (if tedious) ways to combat these beetles is by handpicking them off your plants every day, before they call over their friends. The reason we always find them in groups is twofold. Firstly, the females release an attractant - or pheromone - that lures males. Secondly, when they start to munch, plants release chemical signals that other beetles in flight detect and interpret as "free buffet."

While traps are available, they might actually attract more beetles than they catch, making them more of a double-edged sword. This is because they are baited with the female pheromone, as well as with some of the injured plant signal compounds. However, traps do help scientists keep track of beetle populations, which is key to understanding how to control them.

Natural predators like ants, birds, and even skunks help out a bit, but not enough to make a real dent. But fall does offer a golden opportunity for control efforts. The beetles’ larvae are particularly vulnerable to nematodes that can be applied to lawns, their favourite incubating spots.

Biological control is a promising approach to controlling these beetles. Some scientists have identified a specific parasitic wasp that lays its eggs inside the bodies of the larvae. When they hatch, the wasp larvae eat their host from the inside and emerge as baby wasps. There’s also a fly that could do the job, but introducing new species into an ecosystem is a delicate balance. We don’t want to fix one problem only to create another. With these beetles capable of flying up to 8 km on a windy day, local control efforts can feel like playing whack-a-mole. Just when you think you’ve got them under control, more beetles blow in from neighbouring areas. Unfortunately, there’s no magic wand to wave away this problem. This is why preventing these bugs from hitching a ride across borders is so important.

The Japanese beetle’s journey from Japan to Canada has resulted in a cautionary tale of harm and destruction that can happen when invasive species find new homes. The CFIA works tirelessly to monitor what crosses our borders, from fruit to plants, to stop these unwanted hitchhikers in their tracks. Their efforts highlight the importance of vigilance when it comes to protecting our ecosystems from harmful invaders.

By Renée-Claude Goulet

Beyond the Mines: Navigating the New Era of Synthetic Diamonds

If you've gone ring shopping recently, you might have noticed an increase in discussion of synthetic diamonds as people look for alternatives to the pricey natural diamonds. In the world of diamonds, there are three groups: natural diamonds, diamond simulants and synthetic diamonds. Diamond simulants are other non-diamond stones that are used to mimic diamonds. These simulants can be natural stones such as topaz, or man-made stones like cubic zirconia, which are made in a laboratory. Synthetic diamonds are diamonds made in a lab and have the same physical and chemical properties as natural diamonds.

Close-up of four yellow and one white HPHT synthetic diamonds against a black background

Photo Credit

Bilovitskiy | Wikipedia

Synthetic HPTP diamonds have a variety of shapes such as crosses between cubes and octahedrons.

Natural diamonds are very rare and form deep within the earth, typically between 150 to 200 km below the Earth's surface. They are brought up to the surface by a volcanic eruption that produces vertical columns of rock that rise from deep within the Earth’s mantle to form volcanic rocks known as Kimberlites (or others called Lamproites). For diamonds to form naturally they need temperatures between 900 and 1,300 degrees Celsius and pressure of 5 million kPa (kilopascals) or 725 thousand PSI (pounds per square inch). Diamonds are a mineral with cubic- or octahedral-shaped crystals formed by tight carbon–carbon bonding that are known for the ability to resist scratching and for their shininess and sparkle.

Humans have been able to simulate diamond forming conditions, so it must have been easy to create diamonds, right? Well, not exactly. The first diamonds were made by General Electric in America in 1954 after almost a decade of work. However, General Electric was missing a key ingredient for making a large enough diamond to be considered lab grade. Making a synthetic diamond requires more than just carbon put under the right pressure and temperature conditions in a lab. A nucleation point or “seed” — a piece of diamond where the diamond growth can be contracted into a single crystal — is essential. General Electric was able to grow the first gem-quality diamond in the 1970s using a graphite seed to influence diamond growth.

Today, there are two main ways to grow a diamond: the High pressure and High temperature method (HPHT), and the Chemical Vapour Deposition method (CVD). HPHT diamonds are made — you guessed it — under high pressure and high temperature (higher than their natural counterparts: around 2,000 degrees Celsius and 100 million kPa (kilopascals) or 1.5 million PSI). A diamond slice, or seed, is placed in graphite and a metal powder causing a reaction, allowing for the graphite to melt and transport the carbon onto the diamond seed, creating a new fully formed crystal. The process can produce diamonds with impurities such as metals fragments, or too much nitrogen that can give the diamonds a yellowish colour.

Chemical Vapour deposition diamonds are a little different; they are made within a chamber filled with carbon gas heated by microwaves to around 900 degrees Celsius. Carbon atoms are separated from the gas and rain onto a diamond plate, after several layers are deposited over the seed a cube is made of many microscopic layers. As pure carbon is used in the machine, the diamonds don't have the same impurities that would cause colour, so typically they create a type of diamond known to have no impurities called type IIA (rare in nature).

Synthetic gems are typically cleaner, cheaper, and can come in a wide variety of colours at affordable prices, though they are still considered non-diamonds by some. It's important to understand and appreciate that these are real diamonds that have been made in a lab and have the same chemical and physical properties as their natural counterparts.

By Gordon Bardell

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