Dec 31: Our annual holiday question show

To finish out the year, we've got another edition of our ever-popular Listener Question Show, where we find the experts to answer your burning science questions.

Mark Harnett from Belmont, California asks: Given the recent success of the DART Mission, how much time did the Chicxulub impact take off the Earth's year?

Derek Richardson is the Dynamics Working Group Lead on DART, NASA's recent successful mission to change the orbit of an asteroid. He calculates that while DART reduced the orbital period of the asteroid Dimorphus around its parent asteroid Didymos by about 30 minutes, the Chicxulub impact would have slowed the Earth's orbit by only a few hundredths of a second. 

Patrick Meehan in Victoria BC asks: I'm listening to Bob's 30th anniversary show right now, and every time there's a throwback to a segment from decades ago, Bob's voice sounds much higher in pitch! Why is that?

Dr Karen Kost is with the department of Otolaryngology at McGill University Health Centre.She says that the vocal cords, also known as vocal folds, are largely muscle. Like any other muscle in your body, they change as we get older.

Melanie Scholz in Kitchener ON asks: Me and my daughters Pia and Dana are wondering why many birds, such as chickens and pigeons, bob their heads back and forth when they walk and run? When we tried walking and running like that it made us sort of dizzy.

Scott Macdougall-Shackleton is a professor in psychology and the director of the advanced facility for avian research at Western University. He says that not all birds bob their heads, but for the ones that do, it seems to facilitate their visual perception, like figure skaters who look at one particular point to help them spin on the ice.

John Roman from Mississauga, ON wants to know: Do animals like insects and reptiles play, like we see with many mammalian species? 

Sergio Pellis is a professor of behavioural neuroscience at the University of Lethbridge in Alberta. He says the answer depends on what you consider play, but spiders, reptiles, fish and birds have all been seen engaging in play-like behaviours.

Nick Farina from Powell River BC wants to know: Can trees grow more quickly because of the increased CO2 in the air?

Warner Kurz is a senior research scientist with Canadian Forest Service of Natural Resources Canada in Victoria, BC. He says that CO2 is one of the factors that can limit growth. If we have more of it, it can be easier for trees and plants to extract it from the air which could help them grow more quickly. However plant and tree growth can also be limited by other factors, like nitrogen, water or temperature. 

Rachael Adams in Ottawa ON asks: Given the extensive similarities between different species of mammals, how can gestational periods vary so much? How can an animal as complex as a rabbit be formed in less than a month, when it takes 9 months for a human?

Helen Kurki is an Assistant Professor and Chair in the Department of Anthropology at the University of Victoria. She says it all comes down to an animal's life history strategy. Gestation periods can vary with animal size, and how developed the newborn infants are, all depending on what guarantees the animal better reproductive success. 

Nels Johnson from Edmonton AB wants to know: Are human eyes interchangeable, or are they distinctly left or right like hands and feet?

Ben Thompson is a professor in the school of optometry and vision science at the University of Waterloo. He says the simple answer is yes, we have a distinctive left and right eye and they are not interchangeable. This supports our three-dimensional vision.

Michael Ruxton from Dartmouth, NS wants to know: What are the upper and lower temperature limits that humans can survive in? 

Steven Cheung, a professor of kinesiology and senior research fellow from Brock University, says our comfort zone ranges from 12-15 degrees C to 37 degrees. Going above or below that temperature range without special clothing or a way to regulate the temperature around you is not only dangerous, it can be deadly. 

Owen Wilson from Mississauga, ON asks: Why don't tree roots just rot in the ground like all other buried wood does? 

Nadir Erbilgin is a professor of Forest Entomology and Chemical Ecology at the University of Alberta in Edmonton. He says tree roots, unlike buried wood, are alive, and have an immune system of chemical defenses that work to prevent rot-inducing fungi from getting inside.