She is known for her research using stable isotope mass spectrometry to study a variety of subjects including ancient climates, biogeochemical cycles, animal behavior, ecology, and astrobiology.

Fogel served in many leadership roles, including Program Director at the National Science Foundation in geobiology and low-temperature geochemistry.

She took a gap year before beginning grad school where she traveled in Europe and developed a small jewelry business making pins from eyeglass lenses.

At the University of Texas, Austin, Fogel worked with Chase Van Baalen, Patrick Parker, and F. Robert Tabita on her dissertation, titled “Carbon isotope fractionation by ribulose 1,5-biphosphate carboxylase from various organisms”.

Using stable carbon isotopes, her group determined that Genyornis consumed nearly exclusively C3 plants, and that their cranial morphology indicated a browser reliant upon shrubland.

Because it seems that the Genyornis diet is fairly restrictive, it is likely that the arrival of humans around 55,000 years ago and their burning of land may have caused some megafauna extinction as it changed the vegetation.

However, a team of researchers, including Fogel, found the 𝛿13C of the species to be as much as 13‰ different from contemporaneous vascular plants, suggesting that Prototaxites are in fact heterotrophs, and more likely a fungus.

Using this knowledge, Fogel measured the 𝛿13C values of essential amino acids to indicate whether the ancient human populations consumed primarily maize or were hunter-gatherers.

[17] Beyond human tagged compounds, natural isotope abnormalities occur as a result of various biotic and abiotic processes, and can often be found to vary across regions and species.

Fogel has used carbon, nitrogen, and strontium isotope ratios to study African elephant[21] diet and habitat use in the Amboseli Park in Kenya.

Using these ratios, Fogel has worked on diet studies on California sea otters,[23] butterflies,[24] blue crabs,[25] killer whales,[26] San Joaquin kit foxes,[27] and bald eagles.

[30] In 2012, Steele et al. announced that ten out of the eleven measured martian meteorites contained abiotic macromolecular organic carbon in high-temperature forming minerals (igneous rocks).

[31] In 2012, Marilyn Fogel was elected as a Fellow to the American Association for the Advancement of Science[33] and given the Sigma Xi Distinguished Scientist Award from the UC Merced Chapter.

[3] From 2015 to 2016, Fogel served as the President to the Biogeosciences Section of the American Geophysical Union,[36] and became the Wilbur W. Mayhew Endowed Professor of Geo-Ecology at UC Riverside in 2017.

[43] As a member of the NASA Astrobiology Institute from 1998 to 2010, she served on the Management Team (2004 to 2008) and then as chief scientist (2008) of the Arctic Mars Analog Svalbard Expedition (AMASE).

[44] Marilyn Fogel and her husband, Christopher Swarth, created several endowments to support high school and undergraduate college students.